Hong Y S, Jacobia S J, Packer L, Patel M S
Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, 14214-3000, USA.
Free Radic Biol Med. 1999 Mar;26(5-6):685-94. doi: 10.1016/s0891-5849(98)00243-3.
To examine the stereospecific effects of lipoic compounds on pyruvate metabolism, the effects of R-lipoic acid (R-LA), S-lipoic acid (S-LA) and 1,2-diselenolane-3-pentanoic acid (Se-LA) on the activities of the mammalian pyruvate dehydrogenase complex (PDC) and its catalytic components were investigated. Both S-LA and R-LA markedly inhibited PDC activity; whereas Se-LA displayed inhibition only at higher concentrations. Examination of the effects on the individual catalytic components indicated that Se-LA inhibited the pyruvate dehydrogenase component; whereas R-LA and S-LA inhibited the dihydrolipoamide acetyltransferase component. The three lipoic compounds lowered dihydrolipoamide dehydrogrenase (E3) activity in the forward reaction by about 30 to 45%. The kinetic data of E3 showed that both R-LA and Se-LA are used as substrates by E3 for the reverse reaction. Decarboxylation of [1-14C]pyruvate via PDC by cultured HepG2 cells was not affected by R-LA, but moderately decreased with S-LA and Se-LA. These findings indicate that (i) purified PDC and its catalytic components are affected by lipoic compounds based on their stereoselectivity; and (ii) the oxidation of pyruvate by intact HepG2 cells is not inhibited by R-LA. The later finding with the intact cells is in support of therapeutic role of R-LA as an antioxidant.
为研究硫辛酸化合物对丙酮酸代谢的立体特异性作用，我们考察了R-硫辛酸（R-LA）、S-硫辛酸（S-LA）和1,2-二硒戊环-3-戊酸（Se-LA）对哺乳动物丙酮酸脱氢酶复合体（PDC）及其催化组分活性的影响。S-LA和R-LA均显著抑制PDC活性；而Se-LA仅在较高浓度时才表现出抑制作用。对各催化组分作用的研究表明，Se-LA抑制丙酮酸脱氢酶组分；而R-LA和S-LA抑制二氢硫辛酰胺乙酰转移酶组分。这三种硫辛酸化合物使正向反应中二氢硫辛酰胺脱氢酶（E3）的活性降低了约30%至45%。E3的动力学数据表明，R-LA和Se-LA在逆向反应中均被E3用作底物。培养的HepG2细胞通过PDC对[1-14C]丙酮酸的脱羧作用不受R-LA影响，但S-LA和Se-LA使其适度降低。这些发现表明：（i）纯化的PDC及其催化组分受硫辛酸化合物的立体选择性影响；（ii）完整的HepG2细胞对丙酮酸的氧化作用不受R-LA抑制。完整细胞的这一发现支持了R-LA作为抗氧化剂的治疗作用。
