Solution structure of calmodulin-W-7 complex: the basis of diversity in molecular recognition

Ethanol in the presence of disulfiram (N,N,N',N'-tetraethylthiuram disulfide, an inhibitor of aldehyde dehydrogenase) inhibited liver beta-alanine-oxoglutarate aminotransferase (beta-AlaAT I) activity yet activated tyrosine aminotransferase (TAT) in weanling rats in vivo. The effect on beta-AlaAT I was followed by the inhibitory expression of beta-AlaAT I mRNA. The beta-AlaAT I activity was reduced with a pseudo-first-order profile with time, and the half-life was calculated to be 12.3 +/- 0.83 h with the rate constant (Kd) of 0.056 +/- 0.004 h-1. The synthesis of beta-AlaAT I in rat liver was estimated to be 1.56 x 10(-10) mol/g of wet tissue per hour at a steady state. A combination of ethanol and disulfiram also reduced beta-alanine-pyruvate aminotransferase (beta-AlaAT II) activity to 60% of the control after 24 h.     

Postdetection selection diversity reception with correlated,unequal average power Rayleigh fading signals for π/4-shift QDPSKmobile radio

The diversity gain degradations due to fading correlation and unequal average power are investigated for practical, two-branch postdetection selection diversity reception. The average bit error rate (BER) of π/4-shift QDPSK is theoretically analyzed taking into account additive white Gaussian noise (AWGN), cochannel interference, and multipath channel delay spread; exact diversity gain degradations are calculated. Simple and useful approximate expressions for the gain degradations are also presented     

An optical method for evaluating ion selectivity for calcium signaling pathways in the cell

A method for evaluating a physiologically relevant ion selectivity of Ca2+ signaling pathways in biological cells based on a Ca(2+)-dependent on/off switch for cellular processes via calmodulin (CaM) chemistry is described. CaM serves as a primary ion receptor for Ca2+ and a given CaM-binding peptide as a target for a CaM-Ca2+ complex. Upon accommodating four Ca2+ ions in its binding sites, CaM undergoes a conformational change to form a CaM-Ca(2+)-target peptide ternary complex. This Ca(2+)-induced selective binding of the Ca(2+)-CaM complex to the target peptide was monitored by a surface plasmon resonance (SPR) technique. As a target peptide, a 26-amino acid residue of M13 derived from skeletal muscle myosin light-chain kinase was used. The target peptide was covalently immobilized in the dextran matrix on top of gold, over which sample solutions containing Ca2+ and CaM were injected in a flow system. Ca(2+)-dependent SPR signals were observed for Ca2+ concentrations from 3.2 x 10(-8) to 1.1 x 10(-5) M and it leveled off. The observed SPR signals were explained as due to an increase in the refractive indexes caused by a Ca2+ ion-switched protein/ peptide interaction, i.e., Ca2+ ion to CaM and subsequent additional binding of the thus formed complex with immobilized M13. No SPR signals were however, induced by Mg2+, K+, and Li+ at concentrations as high as 1.0 x 10(-1) M; these results and previous spectroscopic data taken together conclude that these ions do not induce CaM/peptide interaction. Large changes in SPR signals were observed with a Sr2+ ion concentration over 5.1 x 10(-4) M; Sr2+ ion behaved in this case as a strong agonist toward the Ca(2+)-dependent on/off switch of CaM. The present system thus exhibited "physiologically more relevant" ion selectivity in that relevant metal ions could switch on the CaM/peptide or -protein interaction rather than merely be bound to CaM causing no further signal transduction. The potential use of this finding for more widely evaluating cation selectivity toward the Ca2+ signaling process was discussed.     

Molecular Mechanism of Pathogenesis and Treatment Strategies for AL Amyloidosis

In amyloid light-chain (AL) amyloidosis, small B-cell clones (mostly plasma cell clones) present in the bone marrow proliferate and secrete unstable monoclonal free light chains (FLCs), which form amyloid fibrils that deposit in the interstitial tissue, resulting in organ injury and dysfunction. AL amyloidosis progresses much faster than other types of amyloidosis, with a slight delay in diagnosis leading to a marked exacerbation of cardiomyopathy. In some cases, the resulting heart failure is so severe that chemotherapy cannot be administered, and death sometimes occurs within a few months. To date, many clinical studies have focused on therapeutics, especially chemotherapy, to treat this disease. Because it is necessary to promptly lower FLC, the causative protein of amyloid, to achieve a hematological response, various anticancer agents targeting neoplastic plasma cells are used for the treatment of this disease. In addition, many basic studies using human specimens to elucidate the pathophysiology of AL have been conducted. Gene mutations associated with AL, the characteristics of amyloidogenic LC, and the structural specificity of amyloid fibrils have been clarified. Regarding the mechanism of cellular and tissue damage, the mass effect due to amyloid deposition, as well as the toxicity of pre-fibrillar LC, is gradually being elucidated. This review outlines the pathogenesis and treatment strategies for AL amyloidosis with respect to its molecular mechanisms.     

Dextran deposition in reticuloendothelial organs in hemodialysis patients: A forgotten adverse effect of low‐molecular weight dextran

We present two autopsy cases of refractory ascites/hydrothorax associated with systemic deposition of low‐molecular weight dextran that had been used in hemodialysis over an extended period. The most striking autopsy findings in both cases were dense accumulation of dextran‐laden macrophages in sinusoids of reticuloendothelial organs. These accumulated macrophages seemed to have disturbed blood and lymph flow. Based on these findings, we concluded that the persistent ascites and hydrothorax were attributable to systemic deposition of dextran, especially the accumulation of dextran‐laden macrophages in the reticuloendothelial organs. We suggest that dextran solution should immediately be designated as contraindicated for hemodialysis patients.     

Postdetection phase combining diversity for reception of faded DPSK signals

A new postdetection diversity scheme for the differential phase detection of faded DPSK signals is proposed. It combines the detector outputs in proportion to the squared value of each branch signal envelope. The average BER of pi /4-shift quaternary differential phase shift keying (QDPSK) with two-branch diversity is obtained through computer simulations assuming Rayleigh fading. It is found that the proposed diversity is superior to selection diversity by approximately 1.5 dB.<>     

Analysis of catalytic action of transglutaminase induced in human promyelocytic leukemia (HL-60) and human hepatoblastoma (HepG2) cells

Transglutaminase is a calcium-dependent enzyme that catalyzes an amine incorporation and a cross-linking of proteins. Intracellular transglutaminase is induced when human promyelocytic leukemia HL-60 cells are treated with retinoic acid and human hepatoblastoma HepG2 cells, with interleukin-6. To find whether the intracellular reaction catalyzed by transglutaminase increased when the enzyme is induced in these cells, the transglutaminase-catalyzed incorporation of 14C-labeled methylamine into cellular proteins was measured. The incorporation level of the labeled methylamine into proteins of HL-60 and HepG2 cells did not increase after the transglutaminase had been induced. The presence of the calcium ionophore A23187 did not affect these results. These findings suggested that even after the enzyme induction the catalytic action of intracellular transglutaminase is maintained at a constant level in these cells by unknown regulatory mechanism(s).     

A cavity with an appropriate size is the basis of the PPIase activity

Peptidyl-prolyl isomerases (PPIases) are biologically very important enzymes but their catalytic mechanism is not fully understood. Recently, our comprehensive mutational study on a PPIase, human FK506-binding protein 12 (FKBP12), suggested that only presence of a cavity was required for the catalysis. This study, however, could not determine what properties of the cavity were essential for the catalysis. In the present study, we focused on the size of the cavity and examined if an artificial PPIase activity could be achieved by a protein with a cavity of a size similar to that of FKBP12. We designed such a cavity on barnase, a bacterial nuclease without the PPIase-like activity, by a quadruple mutation F56G/R59G/H102Y/Y103G. The mutant barnase successfully exhibited weak yet significant PPIase activity. Furthermore, we searched the Protein Data Bank for proteins natively possessing such a cavity. Two of the identified non-PPIase proteins, alpha-amylase and prolyl endopeptidase, were tested for the PPIase activity and indeed catalyzed the isomerization of peptide bonds. These results suggest that a cavity with an appropriate size is the basis of the PPIase activity.     

Improving the efficiency of pyroelectric conversion

Pyroelectric conversion utilizes low‐grade waste heat as a heat source, and thus produces clean energy. Low‐grade heat is abundant in the various industries and it is practically free. It can be converted to high‐voltage electricity by pyroelectric conversion. Our pyroelectric converter uses copolymer of poly‐vinylidene fluoride with trifluoroethylene [60/40% P(VDF–TrFE)]. Previously, we encountered a substantial power loss due to internal leakage at high temperature and voltage. In order to increase the power output, we examined the effect of polymer purification using solvent extraction. We compared the electrical properties of purified copolymer with those of ‘as‐received’ copolymer. Although we removed only 0.4 wt% of the copolymer by solvent extraction, the electrical resistivity of purified copolymer was 35% higher than that of the ‘as‐received’ copolymer. We also observed that thin films produced using purified copolymer were able to withstand 50% higher electric field before they were ruined by the electrical short circuit. Subsequently, we conducted pyroelectric conversion using 25 µ m thick 60–40% P(VF₂–TrFE) copolymer films. Copolymer purification resulted in a three‐fold increase in net power output. Net power output per unit volume of the ‘as‐received’ copolymer was 95 J L^?1 but it increased to 279 J L^?1 for purified copolymer. © Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources, 2007. Published by John Wiley & Sons, Ltd.