Korotchkina Lioubov G, Sidhu Sukhdeep, Patel Mulchand S
Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, 140 Farber Hall, 3435 Main Street, Buffalo, NY 14214, USA.
Free Radic Res. 2004 Oct;38(10):1083-92. doi: 10.1080/10715760400004168.
The four pyruvate dehydrogenase kinase (PDK) and two pyruvate dehydrogenase phosphatase (PDP) isoenzymes that are present in mammalian tissues regulate activity of the pyruvate dehydrogenase complex (PDC) by phosphorylation/dephosphorylation of its pyruvate dehydrogenase (E1) component. The effect of lipoic acids on the activity of PDKs and PDPs was investigated in purified proteins system. R-lipoic acid, S-lipoic acid and R-dihydrolipoic acid did not significantly affect activities of PDPs and at the same time inhibited PDKs to different extents (PDK1>PDK4 approximately PDK2>PDK3 for R-LA). Since lipoic acids inhibited PDKs activity both when reconstituted in PDC and in the presence of E1 alone, dissociation of PDK from the lipoyl domains of dihydrolipoamide acetyltransferase in the presence of lipoic acids is not a likely explanation for inhibition. The activity of PDK1 towards phosphorylation sites 1, 2 and 3 of E1 was decreased to the same extent in the presence of R-lipoic acid, thus excluding protection of the E1 active site by lipoic acid from phosphorylation. R-lipoic acid inhibited autophosphorylation of PDK2 indicating that it exerted its effect on PDKs directly. Inhibition of PDK1 by R-lipoic acid was not altered by ADP but was decreased in the presence of pyruvate which itself inhibits PDKs. An inhibitory effect of lipoic acid on PDKs would result in less phosphorylation of E1 and hence increased PDC activity. This finding provides a possible mechanism for a glucose (and lactate) lowering effect of R-lipoic acid in diabetic subjects.
哺乳动物组织中存在的四种丙酮酸脱氢酶激酶（PDK）和两种丙酮酸脱氢酶磷酸酶（PDP）同工酶，通过对其丙酮酸脱氢酶（E1）组分进行磷酸化/去磷酸化来调节丙酮酸脱氢酶复合体（PDC）的活性。在纯化的蛋白质体系中研究了硫辛酸对PDK和PDP活性的影响。R-硫辛酸、S-硫辛酸和R-二氢硫辛酸对PDP的活性没有显著影响，同时不同程度地抑制了PDK（对于R-LA，PDK1>PDK4≈PDK2>PDK3）。由于硫辛酸在PDC中重组时以及单独存在E1时均抑制PDK活性，因此在硫辛酸存在下PDK从二氢硫辛酰胺乙酰转移酶的硫辛酰结构域解离不太可能是抑制的原因。在存在R-硫辛酸的情况下，PDK1对E1的磷酸化位点1、2和3的活性降低到相同程度，因此排除了硫辛酸对E1活性位点的保护使其免受磷酸化的可能性。R-硫辛酸抑制PDK2的自磷酸化，表明它直接对PDK发挥作用。R-硫辛酸对PDK1的抑制作用不受ADP影响，但在丙酮酸存在下降低，丙酮酸本身可抑制PDK。硫辛酸对PDK的抑制作用将导致E1的磷酸化减少，从而增加PDC的活性。这一发现为R-硫辛酸在糖尿病患者中降低血糖（和乳酸）的作用提供了一种可能的机制。
