Adjuvant radiation therapy for adenocarcinoma of the rectum

The potential for electron transfer quenching of rose bengal triplet (3RB2-) to compete with energy transfer quenching by oxygen was evaluated. Rate constants for oxidative and reductive quenching were measured in buffered aqueous solution, acetonitrile and in small unilamellar liposomes using laser flash photolysis. Biologically relevant quenchers were used that varied widely in structure, reduction potential and charge. Radical ion yields (phi i) were measured by monitoring the absorption of the rose bengal semireduced (RB.3-) and semioxidized (RB.-) radicals. The results in solution were analyzed as a function of the free energy for electron transfer (delta G) calculated using the Weller equation including electrostatic terms. Exothermic oxidative quenching was about 10-fold faster than exothermic reductive quenching in aqueous solution. The quenching rate constants decreased as delta G approached zero in both aqueous and acetonitrile solution. Exceptions to these generalizations were observed that could be rationalized by specific steric or electrostatic effects or by a change in mechanism. The results suggest that electron transfer reactions with some potential quenchers in cells could compete with formation of singlet oxygen [O2(1 delta g)]. Values of phi i were generally greater for reductive quenching and, for oxidative quenching, greater in acetonitrile than in buffer. Electron transfer quenching of 3RB2- in liposomes, below the phase transition temperature was slower than in solution for both lipid-soluble and water-soluble quenchers indicating that these reactions may not compete with formation of O2(1 delta g) during cell photosensitization.     

Continuous-wave quantum yields of various cobalamins are influenced by competition between geminate recombination and cage escape

Quantum yields of photolysis of the cobalt-carbon bond for three cobalamin compounds were measured with a continuous-wave laser at 442 nm under both aerobic and anaerobic conditions. Aerobically, the initial homolysis product, Co(II) cobalamin, is trapped by oxygen to form aquocobalamin. Use of an excess of the radical trapping reagent 2,2,6,6-tetramethyl-1-piperidinyloxyl, under anaerobic conditions, scavenges the carbon radical and allows detection of the cobalt(II) photoproduct. Quantum yields measured under anaerobic conditions for 5'-deoxyadenosylcobalamin (phi (Co-C alpha),442 = 0.20 +/- 0.03) and methylcobalamin (phi (Co-C alpha),442 = 0.35 +/- 0.03) are in agreement with the values obtained under aerobic conditions (phi (Co-C alpha),442 = 0.19 +/- 0.04 and phi (Co-C alpha),442 = 0.36 +/- 0.04, respectively). Additionally, the quantum yield values for 5'-deoxyadenosylcobalamin and its base-off derivative (phi (Co-C alpha),442 = 0.045 +/- 0.015) match those obtained on a nanosecond time scale [Chen, E., & Chance, M. R. (1990) J. Biol. Chem. 256, 12987-12994]. A comparison of quantum yields obtained anaerobically for 5'-deoxyadenosylcobalamin and methylcobalamin in H2O versus ethylene glycol shows a 4-fold decrease for the former cobalamin and no change for the latter. These quantum yields are evaluated in terms of time-independent radical separation distances.     

Photodissociation of ligands from heme and heme proteins. Effect of temperature and organic phosphate

The effect of temperature on ligand photodissociation from protoheme and the heme proteins hemoglobin (Hb) and myoglobin (Mb) has been examined. The quantum yield of photodissociation (phi) is greater at 40 degrees than at 0 degrees; in general, larger increases are seen in the less photosensitive complexes, while phi does not change in the most photosensitive complexes. The ratio of phi at 40 degrees to phi at 0 degrees is 1.8 for HbCO, 2.3 for n-butyl isocyanide Hb, 2.7 for HbO2, and 1.3 for HbNO, with initial phi values of 0.38, 0.26, 0.028, and 0.003, respectively. This pattern of quantum yield increases is seen in protoheme as well as Hb and Mb ligand photolysis. The allosteric effector inositol hexaphosphate increases the quantum yield of lignad photolysis from hemoglobin. As with temperature, inositol hexaphosphate addition has a larger effect on complexes of low quantum yield; phi increases 1.2-fold for HbCO and 2.2-fold for HbO2 at 0 degrees. The results are discussed in terms of a model containing a photoexcited intermediate (Phillipson, P.E., Ackerson, B.J., and Wyman, J. (1973) Proc. Natl. Acad. Sci. U.S.A. 70, 1550-1553).     

Time-resolved fluorescence studies of dityrosine in the outer layer of intact yeast ascospores

The (time-resolved) fluorescence properties of dityrosine in the outermost layer of the spore wall of Saccharomyces cerevisiae were investigated. Steady-state spectra revealed an emission maximum at 404 nm and a corresponding excitation maximum at 326 nm. The relative fluorescence quantum yield decreased with increasing proton concentration. The fluorescence decay of yeast spores was found to be nonexponential and differed pronouncedly from that of unbound dityrosine in water. Analysis of the spore decay recorded at lambda ex = 323 nm and lambda em = 404 nm by an exponential series (ESM) algorithm revealed a bimodal lifetime distribution with maxima centered at tau 1C = 0.5 ns and tau 2C = 2.6 ns. The relative amplitudes of the two distributions are shown to depend on the emission wavelength, indicating contributions from spectrally different dityrosine chromophores. On quenching the spore fluorescence with acrylamide, a downward curvature of the Stern-Volmer plot was obtained. A multitude of chromophores more or less shielded from solvent in the spore wall is proposed to account for the nonlinear quenching of the total spore fluorescence. Analysis of the fluorescence anisotropy decay revealed two rotational correlation times (phi 1 = 0.9 ns and phi 2 = 30.6 ns) or a bimodal distribution of rotational correlation times (centers at 0.7 ns and 40 ns) when the data were analyzed by the maximum entropy method (MEM). We present a model that accounts for the differences between unbound (aqueous) and bound (incorporated in the spore wall) dityrosine fluorescence. The main feature of the photophysical model for yeast spores is the presence of at least two species of dityrosine chromophores differing in their chemical environments. A hypothetical photobiological role of these fluorophores in the spore wall is discussed: the protection of the spore genome from mutagenic UV light.     

Double tagging recombinant A1- and A2A-adenosine receptors with hexahistidine and the FLAG epitope. Development of an efficient generic protein purification procedure

An expression plasmid for mammalian cells (CLDN10B) has been modified to add nucleotides encoding hexahistidine and the FLAG peptide (H/F) to cDNAs. The new mammalian expression plasmid has been named pDoubleTrouble (pDT). The plasmid and a recombinant baculovirus were used to produce native-and H/F-human A1 and A2A adenosine receptors, optimally expressed in CHO-K1 and Sf9 cells, respectively. Binding to recombinant H/F-A1 receptors (Bmax = 30 pmol/mg protein) was characterized using [3H]8-cyclopentyl-1,3-dipropylxanthine ([3H]CPX) and 125I-N6-aminobenzyladenosine (125I-ABA). Binding to H/F-A2A receptors (Bmax = 48 pmol/mg protein) was characterized using [3H]5'-N-ethylcarboxamidoadenosine ([3H]NECA) and [3H]2-[4-(2-carboxyethyl)phenethylamino]-NECA ([3H]CGS21680). By comparison to native receptors, the addition of H/F to the amino termini of these receptors had no effect on the binding affinities cyclic AMP accumulation in intact cells was not affected by the H/F extension. Anti-FLAG and Ni-nitrilotriacetic acid affinity chromatography resulted in high yield ( >50% overall recovery) of nearly homogeneous deglycosylation with N-glycosidase F. We anticipate that pDT will be generally useful for facilitating the purification in high yield of recombinant receptors and other proteins by single or sequential affinity chromatography steps.     

Activation of two types of Ca2+-permeable nonselective cation channel by endothelin-1 in A7r5 cells

1. In A7r5 cells loaded with the Ca2+ indicator fura-2, we examined the effect of a Ca2+ channel blocker SK&F 96365 on increases in intracellular free Ca2+ concentrations ([Ca2+]i) and Mn2+ quenching of fura-2 fluorescence by endothelin-1 (ET-1). Whole-cell patch-clamp was also performed. 2. Higher concentrations (> or = 10 nM) of ET-1 (higher [ET-1]) evoked a transient peak and a subsequent sustained elevation in [Ca2+]i: removal of extracellular Ca2+ abolished only the latter. A blocker of L-type voltage-operated Ca2+ channel (VOC) nifedipine at 1 microM reduced the sustained phase to about 50%, which was partially sensitive to SK&F 96365 (30 microM). 3. Lower [ET-1] (< or = 1 nM) evoked only a sustained elevation in [Ca2+]i which depends on extracellular Ca2+. The elevation was partly sensitive to nifedipine but not SK&F 96365. 4. In the presence of 1 microM nifedipine, higher [ET-1] increased the rate of Mn2+ quenching but lower [ET-1] had little effect. 5. In whole-cell recordings, both lower and higher [ET-1] induced inward currents at a holding potential of -60 mV with linear I-V relationships and reversal potentials close to 0 mV. The current at lower [ET-1] was resistant to SK&F 96365 but was abolished by replacement of Ca2+ in the bath solution with Mn2+. The current at higher [ET-1] was abolished by the replacement plus SK&F 96365. 6. In a bath solution containing only Ca2+ as a movable cation, ET-1 evoked currents: the current at lower [ET-1] was sensitive to Mn2+, whereas that at higher [ET-1] was partly sensitive to SK&F 96365. 7. These results indicate that in addition to VOC, ET-1 activates two types of Ca2+-permeable nonselective cation channel depending on its concentrations which differ in terms of sensitivity to SK&F 96365 and permeability to Mn2+.     

Developments in core analysis by NMR measurements

For a large suite of consolidated sandstone samples low in shale content we have measured the permeability k, irreducible water saturation Swi, porosity phi, electrical-resistivity formation factor F, porosity by NMR, geometric-mean relaxation times T1g, and stretched-exponential relaxation times T1s. We find that T1g (or T1s) is the decisive parameter for the estimation of k or Swi of porous sandstones by other than direct measurements of these quantities. The additional use of phi or F brings appreciable, but not decisive, improvement. We show isovalue maps of the error factor delta, which show substantial regions of near-minimum values of delta and show basic compatibility of our estimators for permeability with different published estimators. The exponents of T1g (or T1s) in our power-law estimators and those of various published estimators for k are not very far from 2.0 if either or both of phi and F are also used in the estimators.     

Synthesis of novel europium complexes and their photoluminescence properties

Two novel luminescent Eu(III) complexes with the formulas(NIP)Eu(DBM)3 1 and(ENIP)Eu(DBM)3 2(NIP=2-(naphtha-len-1-yl)-1H-imidazo [4,5-f] [1,10] phenanthroline,ENIP=1-ethyl-2-(naphthalen-1-yl)-1H-imidazo [4,5-f] [1,10] phenanthroline,DBM= dibenzoylmethanato) were successfully synthesized and characterized by IR and elemental analysis.The UV-vis absorption spectra and pho-toluminescence properties of the complexes were investigated,and the irradiation at the absorption band between 300-400 nm of europium complexes either in solution or in the solid state led to the emission of a sharp red band at ~610 nm,a characteristic Eu3+ emission due to the transition of 5D0→7F2.Furthermore,the weak emission bands around 587 and 595 nm attributed to 5D0→7F0 and 5D0→7F1 transition were also displayed in the emission spectra.These results demonstrated that the Eu(III) ion was sensitized efficiently by the ligand and displayed photoluminescence with high intensity,narrow half-peak width,and monochromic light.The excited-state lifetimes of 1 and 2 were in the microsecond time scale,but the photoluminescence quantum yield of 2(0.03) was two times higher than that of 1(0.01) which should be at-tributed to the effect of the ethyl substituting in ENIP.     

Fractionation factors and activation energies for exchange of the low barrier hydrogen bonding proton in peptidyl trifluoromethyl ketone complexes of chymotrypsin

NMR investigations have been carried out of complexes between bovine chymotrypsin Aalpha and a series of four peptidyl trifluoromethyl ketones, listed here in order of increasing affinity for chymotrypsin: N-Acetyl-L-Phe-CF3, N-Acetyl-Gly-L-Phe-CF3, N-Acetyl-L-Val-L-Phe-CF3, and N-Acetyl-L-Leu-L-Phe-CF3. The D/H fractionation factors (phi) for the hydrogen in the H-bond between His 57 and Asp 102 (His 57-Hdelta1) in these four complexes at 5 degreesC were in the range phi = 0.32-0.43, expected for a low-barrier hydrogen bond. For this series of complexes, measurements also were made of the chemical shifts of His 57-Hepsilon1 (delta2,2-dimethylsilapentane-5-sulfonic acid 8.97-9. 18), the exchange rate of the His 57-Hdelta1 proton with bulk water protons (284-12.4 s-1), and the activation enthalpies for this hydrogen exchange (14.7-19.4 kcal.mol-1). It was found that the previously noted correlations between the inhibition constants (Ki 170-1.2 microM) and the chemical shifts of His 57-Hdelta1 (delta2, 2-dimethylsilapentane-5-sulfonic acid 18.61-18.95) for this series of peptidyl trifluoromethyl ketones with chymotrypsin [Lin, J., Cassidy, C. S. & Frey, P. A. (1998) Biochemistry 37, 11940-11948] could be extended to include the fractionation factors, hydrogen exchange rates, and hydrogen exchange activation enthalpies. The results support the proposal of low barrier hydrogen bond-facilitated general base catalysis in the addition of Ser 195 to the peptidyl carbonyl group of substrates in the mechanism of chymotrypsin-catalyzed peptide hydrolysis. Trends in the enthalpies for hydrogen exchange and the fractionation factors are consistent with a strong, double-minimum or single-well potential hydrogen bond in the strongest complexes. The lifetimes of His 57-Hdelta1, which is solvent shielded in these complexes, track the strength of the hydrogen bond. Because these lifetimes are orders of magnitude shorter than those of the complexes themselves, the enzyme must have a pathway for hydrogen exchange at this site that is independent of dissociation of the complexes.     

A model of the quaternary structure of the Escherichia coli F1 ATPase from X-ray solution scattering and evidence for structural changes in the delta subunit during ATP hydrolysis

The shape and subunit arrangement of the Escherichia coli F1 ATPase (ECF1 ATPase) was investigated by synchrotron radiation x-ray solution scattering. The radius of gyration and the maximum dimension of the enzyme complex are 4.61 +/- 0.03 nm and 15.5 +/- 0.05 nm, respectively. The shape of the complex was determined ab initio from the scattering data at a resolution of 3 nm, which allowed unequivocal identification of the volume occupied by the alpha3beta3 subassembly and further positioning of the atomic models of the smaller subunits. The delta subunit was positioned near the bottom of the alpha3beta3 hexamer in a location consistent with a beta-delta disulfide formation in the mutant ECF1 ATPase, betaY331W:betaY381C:epsilonS108C, when MgADP is bound to the enzyme. The position and orientation of the epsilon subunit were found by interactively fitting the solution scattering data to maintain connection of the two-helix hairpin with the alpha3beta3 complex and binding of the beta-sandwich domain to the gamma subunit. Nucleotide-dependent changes of the delta subunit were investigated by stopped-flow fluorescence technique at 12 degrees C using N-[4-[7-(dimethylamino)-4-methyl]coumarin-3-yl]maleimide (CM) as a label. Fluorescence quenching monitored after addition of MgATP was rapid [k = 6.6 s-1] and then remained constant. Binding of MgADP and the noncleavable nucleotide analog AMP . PNP caused an initial fluorescent quenching followed by a slower decay back to the original level. This suggests that the delta subunit undergoes conformational changes and/or rearrangements in the ECF1 ATPase during ATP hydrolysis.     

Extended duration of action of rocuronium in postpartum patients

Nine perylenequinones (PQ), including some familiar naturally occurring pigments, were compared for their light-mediated antiviral efficacies. Calphostin C was the most active compound against the two target viruses, herpes simplex virus type 1 and Sindbis virus. Hypocrellins A and B were also very active. However, three cercosporin-like PQ were substantially less active in spite of their high quantum yields of singlet oxygen, whereas phleichrome, another efficient singlet oxygen producer, showed no detectable antiviral activity. One other PQ, which was a very weak singlet oxygen producer, also showed no antiviral activity. None of the active compounds showed significant antiviral activity in the dark. Thus, for some groups of PQ there was correlation between quantum yield of singlet oxygen (1O2) and antiviral efficacy, but there are evidently other structural features of PQ that influence activity.     

Nonphotochemical quenching of excitation energy in photosystem II. A picosecond time-resolved study of the low yield of chlorophyll a fluorescence induced by single-turnover flash in isolated spinach thylakoids

Chlorophyll a fluorescence emission is widely used as a noninvasive measure of a number of parameters related to photosynthetic efficiency in oxygenic photosynthetic organisms. The most important component for the estimation of photochemistry is the relative increase in fluorescence yield between dark-adapted samples which have a maximal capacity for photochemistry and a minimal fluorescence yield (F0) and light-saturated samples where photochemistry is saturated and fluorescence yield is maximal (Fm). However, when photosynthesis is saturated with a short (less than 50 micro(s)) flash of light, which induces only one photochemical turnover of photosystem II, the maximal fluorescence yield is significantly lower (Fsat) than when saturation is achieved with a millisecond duration multiturnover flash (Fm). To investigate the origins of the difference in fluorescence yield between these two conditions, our time-resolved fluorescence apparatus was modified to allow collection of picosecond time-resolved decay kinetics over a short time window immediately following a saturating single-turnover flash (Fsat) as well as after a multiturnover saturating pulse (Fm). Our data were analyzed with a global kinetic model based on an exciton radical pair equilibrium model for photosystem II. The difference between Fm and Fsat was modeled well by changing only the rate constant for quenching of excitation energy in the antenna of photosystem II. An antenna-based origin for the quenching was verified experimentally by the observation that addition of the antenna quencher 5-hydroxy-1,4-naphthoquinone to thylakoids under Fm conditions resulted in decay kinetics and modeled kinetic parameters very similar to those observed under Fsat conditions in the absence of added quinone. Our data strongly support the origin of low fluorescence yield at Fsat to be an antenna-based nonphotochemical quenching of excitation energy in photosystem II which has not usually been considered explicitly in calculations of photochemical and nonphotochemical quenching parameters. The implications of our data with respect to kinetic models for the excited-state dynamics of photosystem II and the practical applications of the fluorescence yield parameters Fm and Fsat to calculations of photochemical yield are discussed.     

Characterization of the three tyrosine residues of delta 5-3-ketosteroid isomerase by time-resolved fluorescence and circular dichroism

delta 5-3-Ketosteroid isomerase (EC 5.3.3.1) of Pseudomonas testosteroni converts delta 5-3-ketosteroids to delta 4-3-ketosteroids via an enolic intermediate. Site-specific mutagenesis has identified Tyr-14 and Asp-38 as the catalytically essential general acid and base, respectively. Three tyrosine residues (Tyr-14, Tyr-55, and Tyr-88) are the only significant fluorophores in the wild-type isomerase. Recent studies of the steady-state fluorescence of the wild-type enzyme and all six mutant enzymes in which one or two tyrosine residues have been mutated to phenylalanine show that the fluorescence intensity of Tyr-14 is very high, that of Tyr-88 is very low, and that of Tyr-55 is intermediate and comparable to that of N-acetyltyrosine amide in solution (Li, Y.-K., Kuliopulos, A., Mildvan, A.S., & Talalay, P. (1993) Biochemistry 32, 1816-1824). Extension of these experiments by time-resolved fluorescence and fluorescence anisotropy measurements demonstrates that Tyr-14, which is in a hydrophobic environment, has an unusually long fluorescence lifetime (4.6 ns) as compared to Tyr-55 (2.0 ns) or Tyr-88 (0.8 ns) and to most protein tyrosine residues (0.2-2 ns). The F?rster distances obtained from the absorption and emission of these tyrosines predict that total quenching of Tyr-14 fluorescence by Tyr-55, and to a lesser degree by Tyr-88, would occur if their orientations were favorable.(ABSTRACT TRUNCATED AT 250 WORDS)     

Coralyne binds tightly to both T.A.T- and C.G.C(+)-containing DNA triplexes

Coralyne is a DNA-binding antitumor antibiotic whose structure contains four fused aromatic rings. The interaction of coralyne with the DNA triplexes poly(dT).poly(dA).poly(dT) and poly[d(TC)].poly[d(GA)].poly[d(C+T)] was investigated by using three techniques. First, Tm values were measured by thermal denaturation analysis. Upon binding coralyne, both triplexes showed Tm values that were increased more than those of the corresponding duplexes. A related drug, berberinium, in which one of the aromatic rings is partially saturated, gave much smaller changes in Tm. Second, the fluorescence of coralyne is quenched in the presence of DNA, allowing the measurement of binding parameters by Scatchard analysis. The binding isotherms were biphasic, which was interpreted in terms of strong intercalative binding and much weaker stacking interactions. In the presence of 2 mM Mg2+, the binding constants to poly(dT).poly-(dA).poly(dT) and poly[d(TC)].poly[d(GA)].poly[(C+T)] were 3.5 x 10(6) M-1 and 1.5 x 10(6) M-1, respectively, while the affinity to the parent duplexes was at least 2 orders of magnitude lower. In the absence of 2 mM Mg2+, the binding constants to poly[d(TC)].poly[d(GA)].poly[d(C+T)] and poly-[d(TC)].poly[d(GA)] were 40 x 10(6) M-1 and 15 x 10(6) M-1, respectively. Thus coralyne shows considerable preference for the triplex structure but little sequence specificity, unlike ethidium, which will only bind to poly(dT).poly(dA).poly(dT). Further evidence for intercalation of coralyne was provided by an increase in the relative fluorescence quantum yield at 260 nm upon binding of coralyne to triplexes as well as an absence of quenching of fluorescence in the presence of Fe[(CN)6]4-.(ABSTRACT TRUNCATED AT 250 WORDS)     

Purification and characterization of recombinant human granulocyte colony-stimulating factor (rhG-CSF) derivatives: KW-2228 and other derivatives

Various derivatives of recombinant human granulocyte colony-stimulating factor (rhG-CSF) have been overproduced in Escherichia coli with the strong, inducible trp promoter. A derivative designated as KW-2228 in which the amino acids were replaced at five positions showed more potent granulopoietic activity and stability than those of wild-type both in vitro and in vivo. The purification involved a sequential renaturation process and three-step chromatography. Refolding succeeded in very high yield using a urea system. The purity of KW-2228 was greater than 99% as measured by SDS-PAGE and HPLC analysis. According to circular dichroism and nuclear magnetic resonance spectroscopy, rhG-CSF and KW-2228 have very similar conformations. This suggests that the substitution of five amino acids does not appreciably change the conformation of hG-CSF. KW-2228 ([Ala1, Thr3, Tyr4, Arg5, and Ser17]-hG-CSF) and derivative A ([Ala1, Thr3, Tyr4, Arg5]-hG-CSF) are easily crystallized and they show similar in vitro activity. On the other hand, neither rhG-CSF nor derivative B ([Ser17]-hG-CSF) are crystallized under the same conditions. Thus, the four amino acid substitution (Ala1, Thr3, Tyr4, Arg5) of the N-terminal sequence may facilitate crystallization. The change of Cys17 to Ser may not influence the stability and activity of hG-CSF.     

Energy transfer (deazaflavin-->FADH2) and electron transfer (FADH2-->T <> T) kinetics in Anacystis nidulans photolyase

DNA photolyases catalyze the photocycloreversion of cyclobutane pyrimidine dimers. The enzyme from the cyanobacterium Anacystis nidulans contains two chromophores, 1,5-dihydroflavin adenine dinucleotide (FADH2) and 7,8-didemethyl-8-hydroxy-5-deazariboflavin (8-HDF). The photophysical/photochemical reactions leading to DNA repair were investigated by using time-resolved and steady-state fluorescence spectroscopy. It was found that the excited singlet state of 8-HDF transfers energy to FADH2 at a rate of 1.9 x 10(10) s-1 and a quantum yield of 0.98. Using the Forster equation for long-range energy transfer and assuming random orientations of the donor and acceptor the interchromophore distance was calculated to be 15 A. The excited singlet FADH2 which forms either by energy transfer from 8-HDF or by direct absorption of a photon has a lifetime of 1.8 ns in the absence of substrate and 0.14 ns in the presence of the photodimer indicating electron transfer from the FADH2 excited singlet state to the dimer at a rate of 6.5 x 10(9) s-1 and quantum efficiency of 92%.     

Change of karyoskeleton during mammalian spermatogenesis: expression pattern of nuclear lamin C2 and its regulation

The photophysical and photochemical properties of porphyrins were profoundly changed upon addition of rhodamine 123. The Soret band of the porphyrins shifted to higher wavelengths, the fluorescence yield of the porphyrins decreased with unaltered decay rates, and their triplet state was quenched. These observations indicate a strong interaction between porphyrins and rhodamine 123 and formation of 1:1 nonfluorescent complexes, of which the binding constants were determined. Illumination of a porphyrin in the presence of rhodamine 123 resulted in the formation of a porphyrin radical cation, which could be detected with ESR spectroscopy. Quenching of the triplet state of the porphyrins by rhodamine 123 resulted in a decreased singlet oxygen yield and a decrease of the photooxidation of histidine, methionine, tyrosine, and tryptophan. However, the oxidation of thiol compounds was increased and the stoichiometry of the reaction between cysteine and oxygen changed from 2 to 3.8 mol cysteine/ mol oxygen. These results show that the presence of rhodamine 123 converted the for porphyrins prevalent energy transfer (type II) reaction to an electron transfer (type I) reaction.     

The synthesis and in vitro activity of some delta 7,9(11)-lanostadienes

The synthesis of delta 7,9(11)-lanostadiene derivatives functionalized at C(32) starting from 3 beta-acetoxy-7 alpha,32-epoxylanostan-11-one has been presented. The delta 7,9(11) moiety was efficiently introduced in three steps in 71% yield by the regioselective abstraction of allylic 8 beta hydrogen. The formyl group of the key intermediate, 3 beta-benzoyloxylanosta-7,9(11)-dien-32-al, has been stereoselectively alkylated into (32S) derivative, whereas its oxidation unexpectedly afforded 3 beta-benzoyloxy-7-oxolanost-8-ene-32,11 alpha-lactone and not the corresponding acid. delta 7,9(11)-lanostadienes possessing HC(32)=O, C(32) [symbol: see text] N, HC(32S)CH3OH, H2C(32)OH, as well as some 11-keto lanostenes, were tested in vitro against several purified cholesterogenic enzymes showing moderate activity, with most the active aldehyde 16 having IC50 = 86 microM.     

Effects of gavage versus dosed feed administration on the toxicokinetics of benzyl acetate in rats and mice

8-epi-prostaglandin F2 alpha stimulated contraction of human myometrial strips obtained from five different donors at the time of hysterectomy with a pEC50 value of 6.3 +/- 0.5. In paired strips from the same donors the pEC50 value for the selective TP receptor agonist U46619 ([1R-[1a,4a,5b(Z),6a(1E,3S*)]]-7-[6-(3- hydroxy-1-octenyl)-2-oxabicyclo[2.2.1]hept-5-yl]-5-heptenoic acid) was 8.3 +/- 0.4. In strips from four other donors 8-epi-prostaglandin F2 alpha was ineffective whereas the pEC50 for U46619 was 6.9 +/- 0.3. Responses to 8-epi-prostaglandin F2 alpha were unaffected by the selective DP receptor antagonist BW A868C (3-benzyl-5-(6-carboxyhexyl)-1-(2- cyclohexyl-2-hydroxyethylamino)hydantoin) at 50 nM but were blocked by the selective TP receptor antagonist L670596 ((-)6,8-difluoro-9-p-methylsulfonyl benzyl-1,2,3,4- tetrahydrocarbazol-1-yl-acetic acid) at 50 nM. The pIC50 values obtained when the TP receptor antagonists GR 32191 ([1R- [1 alpha(Z),2 beta,3 beta,5 alpha]]-(+)-7-[5-[[(1,1'-biphenyl)-4- yl]methoxy]-3-hydroxy-2-(1-piperidinyl)cyclopentyl]-4-heptenoic acid), ICI D1542 ((4(Z)-6-[(2S,4S,5R)-2-[1-methyl-1-(2-nitro-4-tolyloxy)ethyl]- 4-(3-pyridyl)-1,3-dioxan-5-yl]hex-4-enoic acid), ICI 192605 (4(Z)-6-[(2,4,5-cis)-2-(2-chlorophenyl)-4-(2-hydroxyphenyl)-1,3- dioxan-5-yl]hexenoic acid), L670596 and SQ 29548 ([1S-(1 alpha,2 beta(5Z),3 beta,4 alpha]]-7- [3-[[2-[(phenylamino)carbonyl]hydrazino]methyl]-7- oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid) were added cumulatively to strips pre-contracted with an EC80 concentration of 8-epi-prostaglandin F2 alpha were not significantly different from those obtained when an EC80 concentration of U46619 was used. The effects of 8-epi-prostaglandin F2 alpha on strips pre-contracted with an EC80 concentration of U46619 were not different from those of U46619 itself. It is concluded that in the non-pregnant human myometrium 8-epi-prostaglandin F2 alpha is a medium potency contractile agonist acting predominantly at the TP receptor.     

Relations between Quenching Rate and Electrochemical Characteristics of Mm (NiCoMnA1) 5Bx (x=0～0.2) Electrode Alloys

Low-Co AB5-type Mm(NiCoMnA1)5Bx (x = 0, 0.1, 0.2 ) electrode alloys were prepared by casting and rapid quenching.The effects of the rapid quenching on the lattice constants, microstructures and electrochemical characteristics of the alloys were investigated in detail.The obtained results show that the rapid quenching made lattice constants and cell volume increased.In a range of the quenching rate, rapid quenching can increase the discharge capacities of the alloys.However, the discharge capacity of the as-quenched alloy is lower than that of the as-cast alloy when quenching rate is more than a critical value.The cycle lives of the alloys increase monotonously with the increase of the quenching rate.