Intracellular inhibition of UDP-glucose dehydrogenase during ethanol oxidation (original) (raw)
Related papers
Effect of Fructose and Glyceraldehyde on Ethanol Metabolism in Human Liver and in Rat Liver
European Journal of Biochemistry, 1972
The basic kinetic parameters, V and Km, have been determined for liver enzymes involved in the metabolism of fructose and ethanol in rats and man. Values, previously not reported, or which deviate significantly from those reported in the literature are as follows: The maximal activity of aldehyde dehydrogenase from human liver with acetaldehyde as substrate was determined as 43 pmol x min-l x g wet wt-l. The activity of NADP-dependent alcohol dehydrogenase with ethanol as substrate both in rat liver and in human liver was very low. The presence of glycerate kinase (12 pmol x min-l x g wet &-I) in human liver has been established. The K,value of human-liver alcohol dehydrogenase (NAD) for D-glyceraldehyde was determined as 80-90mM compared to 8-10mM for the rat liver enzyme. The NADP-dependent alcohol dehydrogenase from human liver had a Km-value for D-glyceraldehyde of 2.5-3.3 mM. Glycerate kinase from human and rat liver had K,-values for D-glyceraldehyde of 2.5-3.0 mM and 0.03 mM, respectively.
Microsomal UDP-Glucuronyltransferase in Rat Liver: Oxidative Activation
Basic & Clinical Pharmacology & Toxicology, 2005
Activation of microsomal UDP-glucuronyltransferase (UDPGT) activity by treatment of hepatic microsomes with either detergents or Fe 3π /ascorbate pro-oxidant system has been reported; however, definite mechanisms underlying these effects have not been clarified. In this work, we characterize Fe 3π /ascorbate-induced activation of UDPGT activity prior to solubilization with Triton X-100 and after the oxidation process provoked the solubilization of the enzyme. We observed a time-dependent increase in UDPGT activity up to 20 min. incubation of the microsomes with Fe 3π /ascorbate (3-times); after 20 min. incubation, however, we observed a time-dependent decrease in this activity to basal levels after 4 hr incubation. Treatment of microsomes with 0.1% Triton X-100 (5 min.) lead to a similar increase in UDPGT activity; higher detergent concentrations produced a dose-dependent decrease in this activity to basal levels with 1% Triton X-100. Interestingly, UDPGT activity was susceptible to activation only when associated to microsomal membranes and the loss of activation correlated with the solubilization of this activity. UDPGT activation by either Fe 3π /ascorbate or Triton X-100 was correlated with an increase in p-nitrophenol apparent K m and V max values. This activation was prevented or reversed by the reducing agents glutathione, cysteine or dithiothreitol when it was induced by the Fe 3π /ascorbate. Furthermore, the latter provoked a significant decrease in microsomal thiol content, effect not observed after treatment with Triton X-100. Our results suggest that the main mechanism responsible for Fe 3π /ascorbate-induced UDPGT activation is likely to be the promotion of protein sulfhydryl oxidation; this mechanism appears to be different from detergent-induced UDPGT activation.
Ethanol-mediated increase in cytochrome p-450 in cultured hepatocytes
Biochemical Pharmacology, 1981
Cellufar levels of cytochrame P-450 were increased on exposure of cultured chick embryo hepatocytes to ethanol. This increase correlated with increases in the enzymatic activities of both benzphetamine demethylase [associated with the species of P-450 induced by propylisoproplyacetamide (PIA) or phenobarbital] and ethoxyresorufin deethylase [associated with the P-448 species induced by ~naphtho~avone (PNF)]. The increased enzymatic activity relative to P-450 more closely resembled that caused by PIA than by &NF. Glucuronidation of phenol red was also increased by ethanol; the dose response resembled that for increases in cytochrome P-450. PIA induced the giucuronidation of phenol red, whereas /?-NF did not. Therefore, ethanol exposure was found to increase cytochrome P-450 and glucuronyitransferase in these cells in a pattern similar to increases observed with PIA.
Effect of ethanol on glutathione concentration in isolated hepatocytes
The Biochemical journal, 1980
1. Ethanol induces a decrease in GSH (reduced glutathione) concentration is isolated hepatocytes. Maximal effects appear at 20 mM-ethanol. The concentration-dependence of this decrease is paralleled by the concentration-dependence of the activity of alcohol dehydrogenase. 2. Pyrazole, a specific inhibitor of alcohol dehydrogenase, prevents the ethanol-induced GSH depletion. 3. Acetaldehyde, above 0.05 mM, also promotes a decrease in GSH concentration in hepatocytes. 4. Disulfiram (0.05 mM), an inhibitor of aldehyde dehydrogenase, potentiates the fall in GSH concentration caused by acetaldehyde. 5. The findings support the hypothesis that acetaldehyde is responsible for the depletion of GSH induced by ethanol. 6. Methionine prevents the effect of alcohol or acetaldehyde on GSH concentration in hepatocytes.
Alcohol and Alcoholism, 2002
The effects of ethanol on erythrocyte glucose 6-phosphate dehydrogenase (G6PD) activity were investigated under in vitro and in vivo conditions. For in vitro studies, glucose 6-phosphate dehydrogenase was purified from human erythrocyte and rats were used for in vivo studies. Enzyme activity was determined spectrophotometrically by the Beutler method. The in vitro study showed that the I(50) value was 17 mM for ethanol. In the case of the in vivo study, a 2 ml/kg dose of ethanol significantly inhibited the G6PD activity. The inhibition rate after ethanol administration was 59%, 40% and 6% at 1, 3 and 6 h after, respectively. The results of this study suggest that ethanol has a significant inhibitory effect on the G6PD activity both in vivo and in vitro.
The redox-state in relation to ethanol metabolism by rat and guinea pig liver in vitro
Archives of Biochemistry and Biophysics, 1972
Effect of hepatic redox-state on the rate of ethanol metabolism and citric acid cycle activity has been studied in rat and guinea pig liver. Cytoplasmic (NADH)/ (NAD>l ratio in guinea pig liver is about &fold higher than in rat liver. Although, hepatic alcohol dehydrogenase (EC 1.1.1.1) activity is similar in the two species, ethanol metabolism by rat liver in vitro, is about 3 times greater than by guinea pig liver. Addition of ethanol results in a a-fold increase in the hepatic redox-state in the rat but, causes a small increase in the guinea pig. Ethanol-induced increase in hepatic (NADH)/(NAD) ratio, results in a 49-60y0 inhibition of 14COz formation from various radioactive substrates in the rat. However, in guinea pig liver where this ratio is high, W02 formation is already lower by 39-50% than in rat liver and et,hanol addition does not result in a further decrease. The inhibitory effect of ethanol on 'CO2 formation is also observed in rat kidney cortex slices. However, this effect can be abolished by the addition of methylene blue or pyrasole. This study shows that in normal liver cytoplasmic redox-state regulates the rate of ethanol metabolism and that the activity of hepatic alcohol dehydrogenase is not a rate-limiting factor. Furthermore, the inhibitory effect of ethanol on COZ production and therefore on citric acid cycle activity is a consequence of increased (NADH)/(NAD) ratio in liver.