Mauch T J, Donohue T M, Zetterman R K, Sorrell M F, Tuma D J
Hepatology. 1986 Mar-Apr;6(2):263-9. doi: 10.1002/hep.1840060218.
Hepatic ethanol metabolism generates the reactive intermediate, acetaldehyde, which binds to proteins. The binding of acetaldehyde to purified enzymes was determined in order to ascertain whether such binding altered their catalytic functions. [14C]Acetaldehyde was incubated with alcohol dehydrogenase, glucose-6-phosphate dehydrogenase, lactate dehydrogenase and RNase A, each at 37 degrees C (pH 7.4). In some reactions, sodium cyanoborohydride was included for stabilization of Schiff bases, formed as a result of the reaction between acetaldehyde and the amino groups of the enzymes. Portions of each reaction mixture were removed for determination of stable and total (stable plus borohydride-reducible) adducts. Alcohol dehydrogenase and lactate dehydrogenase were not inhibited by adduct formation. Glucose-6-phosphate dehydrogenase and RNase, the activities of which depend on a lysine residue at their catalytic sites, were inhibited in a dose- and time-dependent manner. The degree of inhibition directly correlated with total adduct formation. Phosphate, known to inhibit binding to the active site lysine of RNase, prevented the inhibition of catalytic activity caused by adduct formation. These findings indicate that the binding of acetaldehyde to lysine at the catalytic site can inhibit enzyme activity.
肝脏中的乙醇代谢会产生反应性中间体乙醛，乙醛会与蛋白质结合。为了确定这种结合是否会改变其催化功能，研究人员测定了乙醛与纯化酶的结合情况。将[14C]乙醛分别与乙醇脱氢酶、葡萄糖-6-磷酸脱氢酶、乳酸脱氢酶和核糖核酸酶A在37℃（pH 7.4）下孵育。在一些反应中，加入氰基硼氢化钠以稳定乙醛与酶的氨基反应形成的席夫碱。从每个反应混合物中取出部分样品，用于测定稳定加合物和总加合物（稳定加合物加上硼氢化钠可还原的加合物）。加合物的形成并未抑制乙醇脱氢酶和乳酸脱氢酶的活性。葡萄糖-6-磷酸脱氢酶和核糖核酸酶的活性取决于其催化位点的赖氨酸残基，它们的活性受到剂量和时间依赖性的抑制。抑制程度与总加合物的形成直接相关。已知磷酸盐可抑制与核糖核酸酶活性位点赖氨酸的结合，它能阻止加合物形成所导致的催化活性抑制。这些发现表明，乙醛与催化位点的赖氨酸结合会抑制酶的活性。
