Determination of the angle between the acceptor and anticodon stems of a truncated mitochondrial tRNA

Significant departures from the canonical (cloverleaf) secondary structure of transfer (t)RNAs can be found among the mitochondrial (m)tRNAs of higher metazoans; these mtRNAs thus pose a challenge to the concept of an invariant, L-shaped tertiary conformation for all tRNAs. For bovine mtRNASer(AGY), which lacks the entire "dihydrouridine" (dhU) arm, two distinct tertiary models have been proposed: the first model preserves the L-shaped conformation at the expense of overall size; the second model preserves the absolute distance between the 3' terminus and the anticodon loop, while allowing the acceptor-anticodon interstem angle to vary. We have tested the central predictions of these two models by performing a series of transient electric birefringence measurements on bovine mtRNASer(AGY) constructs in which the aminoacyl-acceptor and anticodon stems were each extended by approximately 70 bp. This mtRNA species is particularly amenable to analysis, since the native bovine (heart) mtRNA is completely unmodified outside of the anticodon loop. For magnesium ion concentrations above 1 mM, the interstem angle for the extended mtRNA, 120(+/-5) degrees, is approximately 50% larger than the corresponding angle for yeast tRNAPhe (70-80 degrees) under the same ionic conditions. Furthermore, the interstem angles of the two tRNAs exhibit strikingly different responses to the addition of magnesium ions: the interstem angle for yeast tRNAPhe is reduced by nearly 50 % upon addition of 2 mM magnesium ions, whereas the angle for mtRNASer(AGY) increases by about 10%. Our data thus support a central prediction of the second model; namely, that truncated mtRNAs will possess more open interstem angles. In addition, we demonstrate that birefringence amplitude data can be used to provide model-independent estimates for the interstem angles.     

Characterization of the radical trapping activity of a novel series of cyclic nitrone spin traps

alpha-Phenyl-tert-butyl nitrone (PBN) is a nitrone spin trap, which has shown efficacy in animal models of oxidative stress, including stroke, aging, sepsis, and myocardial ischemia/reperfusion injury. We have prepared a series of novel cyclic variants of PBN and evaluated them for radical trapping activity in vitro. Specifically, their ability to inhibit iron-induced lipid peroxidation in liposomes was assessed, as well as superoxide anion (O2(-.)) and hydroxyl radical ((.)OH) trapping activity as determined biochemically and using electron spin resonance (ESR) spectroscopy. All cyclic nitrones tested were much more potent as inhibitors of lipid peroxidation than was PBN. The unsubstituted cyclic variant MDL 101,002 was approximately 8-fold more potent than PBN. An analysis of the analogs of MDL 101,002 revealed a direct correlation of activity with lipophilicity. However, lipophilicity does not solely account for the difference between MDL 101,002 and PBN, inasmuch as the calculated octanol/water partition coefficient for MDL 101,002 is 1.01 as compared to 1.23 for PBN. This indicated the cyclic nitrones are inherently more effective radical traps than PBN in a membrane system. The most active compound was a dichloro analog in the seven-membered ring series (MDL 104,342), which had an IC50 of 26 mum, which was 550-fold better than that of PBN. The cyclic nitrones were shown to trap (.)OH with MDL 101,002 being 20 25 times more active than PBN as assessed using 2-deoxyribose and p-nitrosodimethylaniline as substrates, respectively. Trapping of (.)OH by MDL 101,002 was also examined by using ESR spectroscopy. When Fenton's reagent was used, the (.)OH adduct of MDL 101,002 yielded a six-line spectrum with hyperfine coupling constants distinct from that of PBN. Importantly, the half-life of the adduct was nearly 5 min, while that of PBN is less than 1 min at physiologic pH. MDL 101,002 also trapped the O2(-.) radical to yield a six-line spectrum with coupling constants very distinct from that of the (.)OH adduct. In mice, the cyclic nitrones ameliorated the damaging effects of oxidative stress induced by ferrous iron injection into brain tissue. Similar protection was not afforded by the lipid peroxidation inhibitor U74006F, thus implicating radical trapping as a unique feature in the prevention of cell injury. Together, the in vivo activity, the stability of the nitroxide adducts, and the ability to distinguish between trapping of (.)OH and O2(-.) suggest the cyclic nitrones to be ideal reagents for the study of oxidative cell injury.     

Fixation of acetabular cups without cement in total hip arthroplasty. A comparison of three different implant surfaces at a minimum duration of follow-up of five years

OBJECTIVE: To investigate the roles of brain angiotensin II and C-type natriuretic peptide (CNP) in the hypertensive mechanism of deoxycorticosterone acetate (DOCA)-salt hypertension. METHODS: We injected 50 microg/kg CV-11 974, an angiotensin II type-1 receptors antagonist, 30 nmol/kg CNP-22, or the vehicle (artificial cerebrospinal fluid) into the cerebral ventricle or intravenously 5 min before the intracerebroventricular infusion of 1.5 mol/I NaCl solution for 30 min into either male normotensive Wistar rats or DOCA-salt hypertensive rats anesthetized with urethane, and their arterial pressures and heart rates were continuously recorded. Blood (2 ml) was collected at the end of the infusion for the measurement of plasma concentration of arginine vasopressin. We infused 10 or 50 microg/kg per day CV-11 974, 10 or 50 nmol/kg per day CNP-22, or the vehicle (1 microl/h) into the cerebral ventricles of DOCA-salt hypertensive rats for 7 days by using osmotic minipumps, and measured their systolic arterial pressures, pulse rates, and urinary excretions of vasopressin. RESULTS: Intracerebroventricular pre-administrations of CV-11 974 and of CNP-22 inhibited increases in mean arterial pressure, heart rate, and plasma vasopressin concentration induced by intracerebroventricular infusion of 1.5 mol/l NaCl into normotensive rats; increases in hemodynamics and plasma level of vasopressin induced by intracerebroventricular infusion of 1.5 mol/l NaCl were suppressed by intracerebroventricular pre-injections of CV-11 974, but not of CNP-22, into DOCA-salt hypertensive rats. Continuous intracerebroventricular infusions of 50 microg/kg per day CV-11 974 attenuated hypertension in DOCA-salt treated rats, accompanied by a reduction in urinary excretion of vasopressin. Continuous intracerebroventricular infusions of 50 nmol/kg per day CNP-22, however, affected neither hypertension nor urinary excretion of vasopressin in DOCA-salt hypertensive rats. CONCLUSION: Brain angiotensin II could play a role in the pressor mechanism of DOCA-salt hypertension by increasing release of vasopressin via type 1 receptors. That brain CNP has an inhibitory effect on release of vasopressin in acute experiments indicates that the impairment of this inhibitory effect of brain CNP on secretion of vasopressin could be involved in the pathogenesis of DOCA-salt hypertension in rats.     

XR-C1, a new CHO cell mutant which is defective in DNA-PKcs, is impaired in both V(D)J coding and signal joint formation

DNA-dependent protein kinase (DNA-PK) plays an important role in DNA double-strand break (DSB) repair and V(D)J recombination. We have isolated a new X-ray-sensitive CHO cell line, XR-C1, which is impaired in DSB repair and which was assigned to complementation group 7, the group that is defective in the XRCC7 / SCID ( Prkdc ) gene encoding the catalytic subunit of DNA-PK (DNA-PKcs). Consistent with this complementation analysis, XR-C1 cells lackeddetectable DNA-PKcs protein, did not display DNA-PK catalytic activity and were complemented by the introduction of a single human chromosome 8 (providing the Prkdc gene). The impact of the XR-C1 mutation on V(D)J recombination was quite different from that found in most rodent cells defective in DNA-PKcs, which are preferentially blocked in coding joint formation, whereas XR-C1 cells were defective in forming both coding and signal joints. These results suggest that DNA-PKcs is required for both coding and signal joint formation during V(D)J recombination and that the XR-C1 mutant cell line may prove to be a useful tool in understanding this pathway.     

Long-term T cell memory requires the surface expression of self-peptide/major histocompatibility complex molecules

How memory T cells are maintained in vivo is poorly understood. To address this problem, a male-specific peptide (H-Y) was identified and used to activate female anti-H-Y T cells in vitro. Anti-H-Y T cells survived in vivo for at least 70 days in the absence of antigen. This persistence was not because of the intrinsic ability of memory T cells to survive in vivo. Instead, the survival and function of adoptively transferred memory cells was found to require transporter of antigen protein 1-dependent expression of self-peptide/major histocompatibility complex class I molecules in recipient animals. Therefore, it appears that the level of T cell receptor engagement provided by transporter of antigen protein 1-dependent, self-peptide/major histocompatibility complexes is sufficient to maintain the long-term survival and functional phenotype of memory cells in the absence of persistent antigen. These data suggest that positive selection plays a role not only in T cell development but also in the maintenance of T cell memory.     

Evidence for a cyclic GMP-independent mechanism in the anti-platelet action of S-nitrosoglutathione

Using a directed forgetting task, the authors tested in 2 experiments the hypothesis that repressors would be superior to controls in forgetting negative experimental material. Consistent with previous studies, there was an overall directed forgetting effect, with significantly more to-be-remembered material recalled than to-be-forgotten (TBF) material. In both experiments, repressors forgot more negatively valenced words in the TBF set than did nonrepressors, suggesting that repressors have an enhanced capability for using retrieval inhibition. The data offer preliminary support for a cognitive account of repressors' deficits in recalling negative autobiographical memories.