Solomon L R, Crouch J Y
Department of Medicine, Veterans Administration Medical Center, West Haven, Connecticut 06516.
Biochem Med Metab Biol. 1989 Dec;42(3):198-208. doi: 10.1016/0885-4505(89)90056-x.
The mechanism of acetaldehyde-mediated GOT inhibition was studied in human red cells. In the GOT assay mix, acetaldehyde competitively inhibits activation of apoGOT by pyridoxal phosphate and pyridoxamine phosphate. However, Ki values are 100-1000 times greater than Km values for these B6 vitamers. Moreover, incubation of undiluted lysates with acetaldehyde at 37 degrees inhibits GOT activity without increasing apoGOT levels and without altering affinity of apoGOT for either B6 coenzyme. In undiluted lysates, inhibition is not prevented by disulfiram. However, incubation at 4 degrees prevents both acetaldehyde metabolism and GOT inhibition while preincubation with NaF prevents GOT inhibition without affecting acetaldehyde disappearance. The effect of NaF is completely reversed by pyruvate but only partially reversed by NADH. Glyceraldehyde 3-phosphate, the only glycolytic intermediate which directly inhibits GOT, does not reverse the NaF effect. Thus, inhibition of GOT by acetaldehyde (a) requires nonoxidative metabolism of acetaldehyde and (b) is not mediated either by glycolytic substrates or by impaired binding of B6 vitamers to the GOT apoenzyme. Since NaF had no effect on a lysate deficient in glucose 6-phosphate dehydrogenase, the hexose monophosphate shunt may play a role in acetaldehyde-mediated GOT inhibition.
在人红细胞中研究了乙醛介导的谷草转氨酶（GOT）抑制机制。在GOT检测混合物中，乙醛竞争性抑制磷酸吡哆醛和磷酸吡哆胺对脱辅基GOT的激活作用。然而，这些维生素B6的抑制常数（Ki）值比对数（Km）值大100 - 1000倍。此外，未稀释的裂解物与乙醛在37℃孵育会抑制GOT活性，而不会增加脱辅基GOT水平，也不会改变脱辅基GOT对任何一种维生素B6辅酶的亲和力。在未稀释的裂解物中，双硫仑不能阻止抑制作用。然而，在4℃孵育可防止乙醛代谢和GOT抑制，而用氟化钠预孵育可防止GOT抑制，同时不影响乙醛的消失。丙酮酸可完全逆转氟化钠的作用，但烟酰胺腺嘌呤二核苷酸（NADH）只能部分逆转其作用。3 - 磷酸甘油醛是唯一直接抑制GOT的糖酵解中间产物，它不能逆转氟化钠的作用。因此，乙醛对GOT的抑制作用（a）需要乙醛的非氧化代谢，（b）既不是由糖酵解底物介导，也不是由维生素B6与GOT脱辅基酶结合受损介导。由于氟化钠对缺乏葡萄糖6 - 磷酸脱氢酶的裂解物没有影响，磷酸戊糖途径可能在乙醛介导的GOT抑制中起作用。
