EFFECT OF FASTING AND REFEEDING ON ACETYL-COA CARBOXYLASE IN RAT HINDLIMB MUSCLE

Previous studies have demonstrated marked differences in Liver acetyl-CoA carboxylase (ACC) activity between fasted rats and fasted rats refed with a fat-free diet. This study was designed to determine whether skeletal muscle ACC responds to dietary manipulation similarly to liver. Male Sprague-Dawley rats were fasted 48 h (F), fasted 48 h and refed fat-free diet for 48 h (R), or were fed normal rat chow ad libitum (A). Liver ACC, measured on resuspended ammonium sulfate precipitates of 48,000 g supernatants of tissue homogenates, was markedly decreased in F (77 +/- 6 nmol.g(-1).min(-1)) and increased in R (562 +/- 37 nmol.g(-1).min(-1)) rats compared with A rats (210 +/- 23 nmol.g(-1).min(-1)). The citrate concentration required to cause half-maximal activation of liver ACC (K-0.5) was 1.34 +/- 0.14 mM for F, 0.77 +/- 0.09 mM for R, and 0.87 +/- 0.09 mM for A. The quadriceps muscle, on the other hand, showed no difference in ACC activity or in the K-0.5 for citrate activation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blots confirmed the biochemical measurements, showing marked differences in the size of the protein bands in the +260,000 mol wt range in F vs. R Liver ACC preparations but not in skeletal muscle ACC preparations. We conclude that skeletal muscle ACC is controlled by different mechanisms than those observed in liver.