Human skeletal muscle pyruvate dehydrogenase kinase activity increases after a low-carbohydrate diet

To characterize human skeletal muscle enzymatic adaptation to a low-carbohy drate, high-fat, and high-protein diet (LCD), subjects consumed a eucaloric diet consisting of 5% of the total energy intake from carbohydrate, 63% fr om fat, and 33% from protein for 6 days compared with their normal diet (52 % carbohydrate, 33% fat, and 14% protein). Biopsies were taken from the vas tus lateralis before and after 3 and 6 days on a LCD. Intact mitochondria w ere extracted from fresh muscle and analyzed for pyruvate dehydrogenase (PD H) kinase, total PDH, and carnitine palmitoyltransferase I activities and m itochondrial ATP production rate (using carbohydrate and fat substrates). b eta-Hydroxyacyl CoA dehydrogenase, active PDH (PDH,), and citrate synthase activities were also measured on whole muscle homogenates. PDH kinase (PDHK ) was calculated as the absolute value of the apparent first-order rate con stant of the inactivation of PDH in the presence of 0.3 mM Mg2+-ATP. PDHK i ncreased dramatically from 0.10 +/- 0.02 min(-1) to 0.35 +/- 0.09 min(-1) a t 3 days and 0.49 +/- 0.06 min(-1) after 6 days. Resting PDHa activity decr eased from 0.63 +/- 0.17 to 0.17 +/- 0.04 mmol.min(-1).kg(-1) after 6 days on the diet, whereas total PDH activity did not change. Activities for all other enzymes were unaltered by the LCD. In summary, severe deficiency of d ietary carbohydrate combined with a twofold increase in dietary fat and pro tein caused a rapid three- to fivefold increase in PDHK activity in human s keletal muscle. The increased PDHK activity downregulated the amount of PDH in its active form at rest and decreased carbohydrate metabolism. However, an increase in the activities of enzymes involved in fatty acid oxidation did not occur.