Diabetes-induced metabolic abnormalities in myocardium: effect of antioxidant therapy

Effects of hyperglycemia (both diabetes and experimental galactosemia) on cardiac metabolism have been determined. In addition, the effect of supplemental antioxidants on these hyperglycemia-induced abnormalities of cardiac metabolism has been investigated. Diabetes or experimental galactosemia of 2 months duration in rats significantly increased oxidative stress in myocardium, as demonstrated by elevation of thiobarbituric acid reactive substances (TBARS) and lipid fluorescent products in left ventricle. Activity of protein kinase C (PKC) was elevated in the myocardium, and the activities of (Na,K)-ATPase and calcium ATPases were subnormal. Administration of supplemental antioxidants containing a mixture of ascorbic acid, Trolox; alpha-tocopherol acetate, N-acetyl cysteine, beta-carotene, and selenium prevented both the diabetes-induced and galactosemia-induced elevation of oxidative stress and PKC activity, and inhibited the decreases of myocardial (Na,K)-ATPase and calcium ATPases. The results show that these metabolic abnormalities are not unique to diabetes per se, but are secondary to elevated blood hexose levels, and supplemental antioxidants inhibit these metabolic abnormalities. Our findings suggest that antioxidants inhibit abnormal metabolic processes that may contribute to the development of cardiac disease in diabetes, and offer a potential clinical means to inhibit cardiac abnormalities in diabetes.     

Thermus thermophilus contains an eubacterial and an archaebacterial aspartyl-tRNA synthetase

Thermus thermophilus possesses two aspartyl-tRNA synthetases (AspRSs), AspRS1 and AspRS2, encoded by distinct genes. Alignment of the protein sequences with AspRSs of other origins reveals that AspRS1 possesses the structural features of eubacterial AspRSs, whereas AspRS2 is structurally related to the archaebacterial AspRSs. The structural dissimilarity between the two thermophilic AspRSs is correlated with functional divergences. AspRS1 aspartylates tRNA(Asp) whereas AspRS2 aspartylates tRNA(Asp), and tRNA(Asn) with similar efficiencies. Since Asp bound on tRNA(Asn) is converted into Asn by a tRNA-dependent aspartate amidotransferase, AspRS2 is involved in Asn-tRNA(Asn) formation. These properties relate functionally AspRS2 to archaebacterial AspRSs. The structural basis of the dual specificity of T. thermophilus tRNA(Asn) was investigated by comparing its sequence with those of tRNA(Asp) and tRNA(Asn) of strict specificity. It is shown that the thermophilic tRNA(Asn) contains the elements defining asparagine identity in Escherichia coli, part of which being also the major elements of aspartate identity, whereas minor elements of this identity are missing. The structural context that permits expression of aspartate and asparagine identities by tRNA(Asn) and how AspRS2 accommodates tRNA(Asp) and tRNA(Asn) will be discussed. This work establishes a distinct structure-function relationship of eubacterial and archaebacterial AspRSs. The structural and functional properties of the two thermophilic AspRSs will be discussed in the context of the modern and primitive pathways of tRNA aspartylation and asparaginylation and related to the phylogenetic connexion of T. thermophilus to eubacteria and archaebacteria.     

Zinc serum level in human immunodeficiency virus-infected patients in relation to immunological status

In human immunodeficiency virus (HIV) infection, serum level of zinc, an important micronutrient for immune function, is frequently diminished. The aim of this study was to determine the zinc status in relation to immunological parameters and disease stage in 79 HIV-1 seropositive patients. The median serum level of zinc was within normal limits (12.5 micromol/L) but in 23% of patients, zinc deficiency was seen. Decreased serum zinc was associated with a low CD4 cell count, high viral load, and increased neopterin and IgA levels. According to current treatment recommendations, the majority of patients received antiretroviral triple therapy. Zinc levels in treated and untreated patients were comparable. Referring to disease stage (CDC classification, 1993), the mean zinc level was highest in stage C and lowest in stage A. In conclusion, even under antiretroviral triple therapy, zinc deficiency is still of great importance in HIV infection, and zinc substitution in zinc deficient individuals should be taken into account to optimize therapeutical success.     

Effects of medium viscosity on kinetics of the enzymatic reaction catalyzed by bacterial RNase

Effects of medium viscosity on kinetic parameters of poly(U) hydrolysis catalyzed by RNase from Bac. intermedius 7P (binase) were studied in solutions of sucrose (4-50 wt. %) and glycerol (35-62 wt. %) in Tris--sodium acetate buffer (pH 7.5) at 25 degreesC. The rate constant of reaction kcat was practically unchanged over a wide range of viscosities (1-15 cP for sucrose and 2.5-3 cP for glycerol). In glycerol solutions, kcat slightly increased with viscosity increase from 4 to 10 cP. Addition of NaCl to the buffer medium resulted in an inhibitory effect of Na+ on kcat, prevented by 50% sucrose or 60% glycerol. It is concluded that binase-catalyzed poly(U) cleavage occurs through a "tense"-substrate mechanism, similarly to reactions catalyzed by alpha-chymotrypsin, trypsin, and laccase.     

Evidence for a Regulatory Link of Nitrogen Fixation and Photosynthesis in Rhodobacter capsulatus via HvrA

A Rhodobacter capsulatus reporter strain, carrying a constitutively expressed nifA gene and a nifH-lacZ gene fusion, was used for random transposon Tn5 mutagenesis to search for genes required for the NtrC-independent ammonium repression of NifA activity. A mutation in hvrA, which is known to be involved in low-light activation of the photosynthetic apparatus, released both ammonium and oxygen control of nifH expression in this reporter strain, demonstrating a regulatory link of nitrogen fixation and photosynthesis via HvrA. In addition, a significant increase in bacteriochlorophyll a (BChla) content was found in cells under nitrogen-fixing conditions. HvrA was not involved in this up-regulation of BChla. Instead, the presence of active nitrogenase seemed to be sufficient for this process, since no increase in BChla content was observed in different nif mutants.     

Granule-bound starch synthase: structure, function, and phylogenetic utility

Interest in the use of low-copy nuclear genes for phylogenetic analyses of plants has grown rapidly, because highly repetitive genes such as those commonly used are limited in number. Furthermore, because low- copy genes are subject to different evolutionary processes than are plastid genes or highly repetitive nuclear markers, they provide a valuable source of independent phylogenetic evidence. The gene for granule-bound starch synthase (GBSSI or waxy) exists in a single copy in nearly all plants examined so far. Our study of GBSSI had three parts: (1) Amino acid sequences were compared across a broad taxonomic range, including grasses, four dicotyledons, and the microbial homologs of GBSSI. Inferred structural information was used to aid in the alignment of these very divergent sequences. The informed alignments highlight amino acids that are conserved across all sequences, and demonstrate that structural motifs can be highly conserved in spite of marked divergence in amino acid sequence. (2) Maximum-likelihood (ML) analyses were used to examine exon sequence evolution throughout grasses. Differences in probabilities among substitution types and marked among-site rate variation contributed to the observed pattern of variation. Of the parameters examined in our set of likelihood models, the inclusion of among-site rate variation following a gamma distribution caused the greatest improvement in likelihood score. (3) We performed cladistic parsimony analyses of GBSSI sequences throughout grasses, within tribes, and within genera to examine the phylogenetic utility of the gene. Introns provide useful information among very closely related species, but quickly become difficult to align among more divergent taxa. Exons are variable enough to provide extensive resolution within the family, but with low bootstrap support. The combined results of amino acid sequence comparisons, maximum-likelihood analyses, and phylogenetic studies underscore factors that might affect phylogenetic reconstruction. In this case, accommodation of the variable rate of evolution among sites might be the first step in maximizing the phylogenetic utility of GBSSI.