Lee Shou-Lun, Höög Jan-Olov, Yin Shih-Jiun
Department of Biochemistry, National Defense Medical Center, Taipei, Taiwan.
Pharmacogenetics. 2004 Nov;14(11):725-32. doi: 10.1097/00008571-200411000-00003.
Alcohol dehydrogenase (ADH) catalyses the rate-determining reaction in ethanol metabolism. Genetic association studies of diverse ethnic groups have firmly demonstrated that the allelic variant ADH1B2 significantly protects against alcoholism but that ADH1C1, which is in linkage with ADH1B2, produces a negligible protection. The influence of other potential candidate genes/alleles within the human ADH family, ADH1B3 and ADH2, remains unclear or controversial. To address this question, functionalities of ADH1B3 and ADH2 were assessed at a physiological level of coenzyme and substrate range. Ethanol-oxidizing activities of recombinant ADH1B1, ADH1B2, ADH1B3, ADH1C1, ADH1C2 and ADH2 were determined at pH 7.5 in the presence of 0.5 mm NAD with 2-50 mm ethanol. The activity differences between ADH1B2 and ADH1B1 were taken as a threshold for effective protection against alcoholism and those between ADH1C1 and ADH1C2 as a threshold for null protection. Over 2-50 mm ethanol, the activities of ADH1B3 were found 2.9-23-fold lower than those of ADH1B2, largely attributed to the Km effect (ADH1B2, 1.8 mm; ADH1B3, 61 mm). Strikingly, the ADH1B3 activity was only 84% that of ADH1B1 at a low ethanol concentration, 2 mm, but increased 10-fold at 50 mm. Corrected for relative expression levels of the enzyme in liver, the hepatic ADH2 activities were estimated to be 18-97% those of ADH1B1 over 2-50 mm ethanol and were 28-140% of the activity differences between ADH1C1 and ADH1C2. The assessment based on the proposed functional window for the human ADH gene family indicates that ADH1B*3 may show some degree of protection against alcoholism and that the ADH2 functional variants appear to be negligible for this protection.
乙醇脱氢酶（ADH）催化乙醇代谢中的限速反应。对不同种族群体的基因关联研究已确凿表明，等位基因变体ADH1B2能显著预防酒精中毒，但与ADH1B2连锁的ADH1C1产生的预防作用可忽略不计。人类ADH家族中其他潜在候选基因/等位基因ADH1B3和ADH2的影响仍不明确或存在争议。为解决这一问题，在辅酶和底物范围的生理水平上评估了ADH1B3和ADH2的功能。在pH 7.5、存在0.5 mM NAD以及2 - 50 mM乙醇的条件下，测定了重组ADH1B1、ADH1B2、ADH1B3、ADH1C1、ADH1C2和ADH2的乙醇氧化活性。将ADH1B2与ADH1B1之间的活性差异作为有效预防酒精中毒的阈值，将ADH1C1与ADH1C2之间的活性差异作为无效预防的阈值。在2 - 50 mM乙醇范围内，发现ADH1B3的活性比ADH1B2低2.9 - 23倍，这主要归因于Km效应（ADH1B2为1.8 mM；ADH1B3为61 mM）。令人惊讶的是，在低乙醇浓度2 mM时，ADH1B3的活性仅为ADH1B1的84%，但在50 mM时增加了10倍。校正肝脏中该酶的相对表达水平后，估计在2 - 50 mM乙醇范围内，肝脏ADH2的活性为ADH1B1的18% - 97%，且为ADH1C1与ADH1C2活性差异的28% - 140%。基于所提出的人类ADH基因家族功能窗口的评估表明，ADH1B*3可能对酒精中毒表现出一定程度的预防作用，而ADH2功能变体对这种预防作用似乎可忽略不计。
