CONTRIBUTION OF ACIDIC ADH(CLASS III) TO ALCHOL METABOLISM

(1)当以血液水平（15-100 mM）的浓度使用乙醇作为底物时，小鼠肝脏的酸性醇脱氢酶（III类ADH）活性的分数相当于已知为体内醇代谢关键酶的碱性ADH（I类）活性的10-42%。(2)酸性ADH的活性随反应液疏水性的增加而增强。这种活化是由于催化效率（Kcat/Km）的显著增加，基于乙醇的Km的显著降低。另一方面，碱性ADH的活性随着溶液疏水性的增加而受到强烈的抑制。(3)研究发现酸性抗利尿激素主要分布在小鼠肝脏的窦内皮细胞中，而碱性抗利尿激素则分布在肝细胞的细胞质基质中。用疏水探针（尼罗红）对肝组织进行染色，结果表明肝细胞质是疏水的，而且肝窦细胞内的疏水性更强 ...更多信息 l细胞中的细胞比实质细胞中的细胞多。这些结果表明，细胞内的酸性ADH活性较高，而碱性ADH活性降低细胞内的疏水性的影响，与传统的体外方法测量的活性相比。(4)在一种被称为“ADH^-”的鹿鼠肝脏中发现了III类ADH，这种鹿鼠的酒精代谢能力比“ADH^+”鹿鼠高出50%。“ADH^-”菌株遗传缺陷的一类ADH被鉴定为I类。(5)通过在以3.0 g/kg的剂量给予乙醇后额外给予特异性抑制剂（用于碱性ADH的己酰胺和用于过氧化氢酶的氨基三唑），估计碱性ADH和过氧化氢酶对小鼠中总乙醇代谢的贡献分别为约50%和20%（i.）。4-甲基吡唑不仅抑制I类ADH，而且抑制III类ADH和过氧化氢酶途径，几乎完全抑制总代谢。结合体外研究结果，酒精代谢约占总代谢的30%，与I类抗利尿激素和过氧化氢酶无关，推测是由酸性抗利尿激素引起的，因此，结论是酸性ADH（III类）可能在体内酒精代谢中起重要作用，（I类和III类）对代谢的调节响应于细胞内疏水性。少

(1) A fraction of acidic alcohol dehydrogenase (Class III ADH) activity of the mouse liver corresponded to 10-42% that of basic ADH (Class I) known as a key enzyme in alcohol metabolism in vivo, when ethanol was used as a substrate at concentrations of blood level (15-100 mM).(2) The activity of acidic ADH was enhanced with the increase in hydrophobicity of the reaction solution. This activation was due to a marked increase of the catalytic efficiency (Kcat/Km), based on a marked decrease of the Km for ethanol. On the other had, the activity of basic ADH was strongly depressed with the increase in the solution hydrophobicity.(3) Acidic ADH was found to localize mainly in the sinusoidal endothelial cells of the mouse liver, whereas basic ADH was shown to distribute within the cytoplasmic matrix of hepatocytes. Staining the liver tissues with a hydrophobic probe (Nile red) showed that the cytoplasm was hydrophobic, and moreover, the intracelluar hydrophobicity was higher in the sinusoida … More l cells than in the parenchymal cells. These results suggest that intracellular acidic ADH activity was highted, whereas the basic ADH activity was lowered by the effects of intracellular hydrophobicity, compared with their activities measured by the conventional in vitro method.(4) Class III ADH was found in the liver of a so-called "ADH^-" deermouse that possessed a capacity of alcohol metabolism more than 50% that of a "ADH^+" strain. A class of ADH which "ADH^-" strain was genetically deficient in was identified as class I.(5) The contributions of basic ADH and catalase to the total alcohol metabolism in the mouse were estimated to be about 50% and 20%, respectively, by additional administration of specific inhibitors (capronamide for basic ADH and aminotriazole for catalase) after ethanol administration at a dose of 3.0 g/kg (i. p.). The total metabolism was almost completely depressed by adminstration of 4-methylpyrazole, which inhibited not only class I ADH, but also class III ADH and catalase pathway. Taken together with the results from in vitro studies, the alcohol metabolism accounting for about 30% of the total one, which was independent to class I ADH and catalase, was suggested to be due to acidic ADH.Thus, it was concluded that acidic ADH (Class III) may play an important role in alcohol metabolism in vivo and the contributions of the two major ADHs (Class I and III) to the metabolism were reversely regulated in response to the intracellular hydrophobicity. Less