Wagner F W, Parés X, Holmquist B, Vallee B L
Biochemistry. 1984 May 8;23(10):2193-9. doi: 10.1021/bi00305a014.
chi-Alcohol dehydrogenase (chi-ADH), a class III isozyme characterized by its anodic electrophoretic mobility and lack of inhibition by 4-methylpyrazole, has been isolated from human liver and purified to homogeneity in a reducing medium. chi-ADH resembles other human liver ADH isozymes of classes I and II with respect to its molecular weight, dimeric structure, stoichiometry of zinc and NADH binding, and pH optima for the oxidation of alcohols. This homodimer exhibits subtle differences in its absorption spectrum and amino acid composition relative to those of other human isozymes but differs markedly from their specificity toward alcohols and aldehydes. chi-ADH oxidizes ethanol very poorly. The reaction is bimolecular, and an apparent Km cannot be discerned up to 2.3 M ethanol. The enzyme is inactive toward methanol, ethylene glycol, digitoxigenin, digoxigenin, and gitoxigenin , but alcohols with carbon chain lengths greater than four are oxidized rapidly with Km values decreasing with increasing carbon chain length. Taken jointly, the composition, structure, and enzymatic properties of the ADH isozymes purified and studied so far strongly imply that their metabolic roles, yet to be discovered, will give a new perspective to ethanol metabolism and pathology.
Ⅲ类同工酶chi-乙醇脱氢酶（chi-ADH），其特征在于阳极电泳迁移率且不受4-甲基吡唑抑制，已从人肝脏中分离出来，并在还原介质中纯化至同质。chi-ADH在分子量、二聚体结构、锌和NADH结合的化学计量以及醇氧化的最适pH值方面与其他Ⅰ类和Ⅱ类人肝脏ADH同工酶相似。相对于其他人同工酶，这种同型二聚体在吸收光谱和氨基酸组成上表现出细微差异，但在对醇和醛的特异性上与它们有显著不同。chi-ADH氧化乙醇的能力很差。该反应是双分子反应，在乙醇浓度高达2.3 M时无法辨别表观Km值。该酶对甲醇、乙二醇、洋地黄毒苷、地高辛和吉托辛无活性，但碳链长度大于4的醇类可被快速氧化，Km值随碳链长度增加而降低。综合来看，目前纯化和研究的ADH同工酶的组成、结构和酶学性质强烈暗示，它们尚未被发现的代谢作用将为乙醇代谢和病理学提供新的视角。
