Plapp Bryce V, Leidal Kevin G, Murch Bruce P, Green David W
Department of Biochemistry, The University of Iowa, Iowa City, IA 52242, USA.
Chem Biol Interact. 2015 Jun 5;234:85-95. doi: 10.1016/j.cbi.2014.12.040. Epub 2015 Jan 29.
The kinetics of oxidation of various alcohols by purified rat liver alcohol dehydrogenase (ADH) were compared with the kinetics of elimination of the alcohols in rats in order to investigate the roles of ADH and other factors that contribute to the rates of metabolism of alcohols. Primary alcohols (ethanol, 1-propanol, 1-butanol, 2-methyl-1-propanol, 3-methyl-1-butanol) and diols (1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol) were eliminated in rats with zero-order kinetics at doses of 5-20 mmol/kg. Ethanol was eliminated most rapidly, at 7.9 mmol/kgh. Secondary alcohols (2-propanol-d7, 2-propanol, 2-butanol, 3-pentanol, cyclopentanol, cyclohexanol) were eliminated with first order kinetics at doses of 5-10 mmol/kg, and the corresponding ketones were formed and slowly eliminated with zero or first order kinetics. The rates of elimination of various alcohols were inhibited on average 73% (55% for 2-propanol to 90% for ethanol) by 1 mmol/kg of 4-methylpyrazole, a good inhibitor of ADH, indicating a major role for ADH in the metabolism of the alcohols. The Michaelis kinetic constants from in vitro studies (pH 7.3, 37 °C) with isolated rat liver enzyme were used to calculate the expected relative rates of metabolism in rats. The rates of elimination generally increased with increased activity of ADH, but a maximum rate of 6±1 mmol/kg h was observed for the best substrates, suggesting that ADH activity is not solely rate-limiting. Because secondary alcohols only require one NAD(+) for the conversion to ketones whereas primary alcohols require two equivalents of NAD(+) for oxidation to the carboxylic acids, it appears that the rate of oxidation of NADH to NAD(+) is not a major limiting factor for metabolism of these alcohols, but the rate-limiting factors are yet to be identified.
为了研究乙醇脱氢酶（ADH）以及其他影响酒精代谢速率的因素所起的作用，对纯化的大鼠肝脏乙醇脱氢酶氧化各种醇类的动力学与大鼠体内醇类消除的动力学进行了比较。伯醇（乙醇、1-丙醇、1-丁醇、2-甲基-1-丙醇、3-甲基-1-丁醇）和二醇（1,3-丙二醇、1,3-丁二醇、1,4-丁二醇、1,5-戊二醇）在大鼠体内以零级动力学消除，剂量为5 - 20 mmol/kg。乙醇消除最快，为7.9 mmol/kgh。仲醇（2-丙醇-d7、2-丙醇、2-丁醇、3-戊醇、环戊醇、环己醇）在剂量为5 - 10 mmol/kg时以一级动力学消除，相应的酮类生成并以零级或一级动力学缓慢消除。1 mmol/kg的4-甲基吡唑（一种良好的ADH抑制剂）平均抑制了各种醇类消除速率的73%（2-丙醇为55%，乙醇为90%），表明ADH在醇类代谢中起主要作用。体外研究（pH 7.3，37°C）中分离的大鼠肝脏酶的米氏动力学常数用于计算大鼠体内预期的相对代谢速率。消除速率通常随ADH活性增加而增加，但最佳底物的最大速率为6±1 mmol/kg h，这表明ADH活性并非唯一的限速因素。由于仲醇转化为酮类仅需一个NAD(+)，而伯醇氧化为羧酸需要两当量的NAD(+)，因此看来NADH氧化为NAD(+) 的速率并非这些醇类代谢的主要限制因素，但限速因素仍有待确定。
