Hsp60 is targeted to a cryptic mitochondrion-derived organelle ("crypton") in the microaerophilic protozoan parasite Entamoeba histolytica.
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Entamoeba histolytica is a microaerophilic protozoan parasite in which neither mitochondria nor mitochondrion-derived organelles have been previously observed. Recently, a segment of an E. histolytica gene was identified that encoded a protein similar to the mitochondrial 60-kDa heat shock protein (Hsp60 or chaperonin 60), which refolds nuclear-encoded proteins after passage through organellar membranes. The possible function and localization of the amebic Hsp60 were explored here. Like Hsp60 of mitochondria, amebic Hsp60 RNA and protein were both strongly induced by incubating parasites at 42 degreesC. 5' and 3' rapid amplifications of cDNA ends were used to obtain the entire E. histolytica hsp60 coding region, which predicted a 536-amino-acid Hsp60. The E. histolytica hsp60 gene protected from heat shock Escherichia coli groEL mutants, demonstrating the chaperonin function of the amebic Hsp60. The E. histolytica Hsp60, which lacked characteristic carboxy-terminal Gly-Met repeats, had a 21-amino-acid amino-terminal, organelle-targeting presequence that was cleaved in vivo. This presequence was necessary to target Hsp60 to one (and occasionally two or three) short, cylindrical organelle(s). In contrast, amebic alcohol dehydrogenase 1 and ferredoxin, which are bacteria-like enzymes, were diffusely distributed throughout the cytosol. We suggest that the Hsp60-associated, mitochondrion-derived organelle identified here be named "crypton," as its structure was previously hidden and its function is still cryptic. (+info)
Ciprofloxacin decreases the rate of ethanol elimination in humans.
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BACKGROUND: Extrahepatic ethanol metabolism is postulated to take place via microbial oxidation in the colon, mediated by aerobic and facultative anaerobic bacteria. AIMS: To evaluate the role of microbial ethanol oxidation in the total elimination rate of ethanol in humans by reducing gut flora with ciprofloxacin. METHODS: Ethanol was administered intravenously at the beginning and end of a one week period to eight male volunteers. Between ethanol doses volunteers received 750 mg ciprofloxacin twice daily. RESULTS: A highly significant (p=0.001) reduction in the ethanol elimination rate (EER) was detected after ciprofloxacin medication. Mean (SEM) EER was 107.0 (5.3) and 96.9 (4.8) mg/kg/h before and after ciprofloxacin, respectively. Faecal Enterobacteriaceae and Enterococcus sp. were totally absent after medication, and faecal acetaldehyde production capacity was significantly (p<0.05) decreased from 0.91 (0.15) to 0.39 (0.08) nmol/min/mg protein. Mean faecal alcohol dehydrogenase (ADH) activity was significantly (p<0. 05) decreased after medication, but ciprofloxacin did not inhibit human hepatic ADH activity in vitro. CONCLUSIONS: Ciprofloxacin treatment decreased the ethanol elimination rate by 9.4%, with a concomitant decrease in intestinal aerobic and facultative anaerobic bacteria, faecal ADH activity, and acetaldehyde production. As ciprofloxacin has no effect on liver blood flow, hepatic ADH activity, or cytochrome CYP2E1 activity, these effects are probably caused by the reduction in intestinal flora. (+info)
Diet, genetic susceptibility and human cancer etiology.
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There is evidence that high penetrance hereditary genes cause a number of relatively uncommon tumors in the familial setting, whereas common cancers are influenced by multiple loci that alter susceptibility to cancer and other conditions. The latter category of genes are involved in the metabolism of carcinogens (activation, detoxification) as well as those that interact with dietary exposure. This paper will consider some of the basic principles in studying susceptibility genes and provide a few examples in which they interact with dietary components. (+info)
Ciprofloxacin administration decreases enhanced ethanol elimination in ethanol-fed rats.
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Many colonic aerobic bacteria possess alcohol dehydrogenase (ADH) activity and are capable of oxidizing ethanol to acetaldehyde. Accordingly, some ingested ethanol can be metabolized in the colon in vivo via the bacteriocolonic pathway for ethanol oxidation. By diminishing the amount of aerobic colonic bacteria with ciprofloxacin treatment, we recently showed that the bacteriocolonic pathway may contribute up to 9% of total ethanol elimination in naive rats. In the current study we evaluated the role of the bacteriocolonic pathway in enhanced ethanol metabolism following chronic alcohol administration by diminishing the amount of gut aerobic flora by ciprofloxacin treatment. We found that ciprofloxacin treatment totally abolished the enhancement in ethanol elimination rate (EER) caused by chronic alcohol administration and significantly diminished the amount of colonic aerobic bacteria and faecal ADH activity. However, ciprofloxacin treatment had no significant effects on the hepatic microsomal ethanol-oxidizing system, hepatic ADH activity or plasma endotoxin level. Our data suggest that the decrease in the amount of the aerobic colonic bacteria and in faecal ADH activity by ciprofloxacin is primarily responsible for the decrease in the enhanced EER in rats fed alcohol chronically. Extrahepatic ethanol metabolism by gastrointestinal bacteria may therefore contribute significantly to enhanced EER. (+info)
Linkage disequilibrium at the ADH2 and ADH3 loci and risk of alcoholism.
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Two of the three class I alcohol dehydrogenase (ADH) genes (ADH2 and ADH3) encode known functional variants that act on alcohol with different efficiencies. Variants at both these genes have been implicated in alcoholism in some populations because allele frequencies differ between alcoholics and controls. Specifically, controls have higher frequencies of the variants with higher Vmax (ADH2*2 and ADH3*1). In samples both of alcoholics and of controls from three Taiwanese populations (Chinese, Ami, and Atayal) we found significant pairwise disequilibrium for all comparisons of the two functional polymorphisms and a third, presumably neutral, intronic polymorphism in ADH2. The class I ADH genes all lie within 80 kb on chromosome 4; thus, variants are not inherited independently, and haplotypes must be analyzed when evaluating the risk of alcoholism. In the Taiwanese Chinese we found that, only among those chromosomes containing the ADH3*1 variant (high Vmax), the proportions of chromosomes with ADH2*1 (low Vmax) and those with ADH2*2 (high Vmax) are significantly different between alcoholics and controls (P<10-5). The proportions of chromosomes with ADH3*1 and those with ADH3*2 are not significantly different between alcoholics and controls, on a constant ADH2 background (with ADH2*1, P=.83; with ADH2*2, P=.53). Thus, the observed differences in the frequency of the functional polymorphism at ADH3, between alcoholics and controls, can be accounted for by the disequilibrium with ADH2 in this population. (+info)
Biochemical characterization of the small heat shock protein IbpB from Escherichia coli.
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Escherichia coli IbpB was overexpressed in a strain carrying a deletion in the chromosomal ibp operon and purified by refolding. Under our experimental conditions, IbpB exhibited pronounced size heterogeneity. Basic oligomers, roughly spherical and approximately 15 nm in diameter, interacted to form larger particles in the 100-200-nm range, which themselves associated to yield loose aggregates of micrometer size. IbpB suppressed the thermal aggregation of model proteins in a concentration-dependent manner, and its CD spectrum was consistent with a mostly beta-pleated secondary structure. Incubation at high temperatures led to a partial loss of secondary structure, the progressive exposure of tryptophan residues to the solvent, the dissociation of high molecular mass aggregates into approximately 600-kDa oligomers, and an increase in surface hydrophobicity. Structural changes were reversible between 37 and 55 degrees C, and, up to 55 degrees C, hydrophobic sites were reburied upon cooling. IbpB exhibited a biphasic unfolding trend upon guanidine hydrochloride (GdnHCl) treatment and underwent comparable conformational changes upon melting and during the first GdnHCl-induced transition. However, hydrophobicity decreased with increasing GdnHCl concentrations, suggesting that efficient exposure of structured hydrophobic sites involves denaturant-sensitive structural features. By contrast, IbpB hydrophobicity rose at high NaCl concentrations and increased further at high temperatures. Our results support a model in which temperature-driven conformational changes lead to the reversible exposure of normally shielded binding sites for nonnative proteins and suggest that both hydrophobicity and charge context may determine substrate binding to IbpB. (+info)
Nonsense mutations in the alcohol dehydrogenase gene of Drosophila melanogaster correlate with an abnormal 3' end processing of the corresponding pre-mRNA.
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From bacteria to mammals, mutations that generate premature termination codons have been shown to result in the reduction in the abundance of the corresponding mRNA. In mammalian cells, more often than not, the reduction happens while the RNA is still associated with the nucleus. Here, it is reported that mutations in the alcohol dehydrogenase gene (Adh) of Drosophila melanogaster that generate premature termination codons lead to reduced levels of cytoplasmic and nuclear mRNA. Unexpectedly, it has been found that the poly(A) tails of Adh mRNAs and pre-mRNAs that carry a premature termination codon are longer than in the wild-type transcript. The more 5' terminal the mutation is, the longer is the poly(A) tail of the transcript. These findings suggest that the integrity of the coding region may be required for accurate mRNA 3' end processing. (+info)
Drosophila lebanonensis alcohol dehydrogenase: pH dependence of the kinetic coefficients.
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The alcohol dehydrogenase (ADH) from Drosophila lebanonensis shows 82% positional identity to the alcohol dehydrogenases from Drosophila melanogaster. These insect ADHs belong to the short-chain dehydrogenase/reductase family which lack metal ions in their active site. In this family, it appears that the function of zinc in medium chain dehydrogenases has been replaced by three amino acids, Ser138, Tyr151 and Lys155. The present work on D. lebanonensis ADH has been performed in order to obtain information about reaction mechanism, and possible differences in topology and electrostatic properties in the vicinity of the catalytic residues in ADHs from various species of Drosophila. Thus the pH dependence of various kinetic coefficients has been studied. Both in the oxidation of alcohols and in the reduction of aldehydes, the reaction mechanism of D. lebanonensis ADH in the pH 6-10 region was consistent with a compulsory ordered pathway, with the coenzymes as the outer substrates. Over the entire pH region, the rate limiting step for the oxidation of secondary alcohols such as propan-2-ol was the release of the coenzyme product from the enzyme-NADH complex. In the oxidation of ethanol at least two steps were rate limiting, the hydride transfer step and the dissociation of NADH from the binary enzyme-NADH product complex. In the reduction of acetaldehyde, the rate limiting step was the dissociation of NAD+ from the binary enzyme-NAD+ product complex. The pH dependences of the kon velocity curves for the two coenzymes were the opposite of each other, i.e. kon increased for NAD+ and decreased for NADH with increasing pH. The two curves appeared complex and the kon velocity for the two coenzymes seemed to be regulated by several groups in the free enzyme. The kon velocity for ethanol and the ethanol competitive inhibitor pyrazole increased with pH and was regulated through the ionization of a single group in the binary enzyme-NAD+ complex, with a pKa value of 7.1. The kon velocity for acetaldehyde was pH independent and showed that in the enzyme-NADH complex, the pKa value of the catalytic residue must be above 10. The koff velocity of NAD+ appeared to be partly regulated by the catalytic residue, and protonation resulted in an increased dissociation rate. The koff velocity for NADH and the hydride transfer step was pH independent. In D. lebanonensis ADH, the pKa value of the catalytic residue was 0.5 pH units lower than in the ADHS alleloenzyme from D. melanogaster. Thus it can be concluded that while most of the topology of the active site is mainly conserved in these two distantly related enzymes, the microenvironment and electrostatic properties around the catalytic residues differ. (+info)