Acetyl Coenzyme A Carboxylase

Feeding a low fat, biotin-deficient diet to young rats for 1 to 2 weeks leads to a decrease in acetyl coenzyme A carboxylase levels in epididymal adipose tissue with accumulation of the apoenzyme. These changes occur prior to changes in hepatic propionyl coenzyme A carboxylase levels. Acetyl coenzyme A carboxylase levels in liver decrease minimally with biotin deficiency, and little apoenzyme accumulates. The presence of apoenzyme in adipose tissue of deficient rats was initially suggested by the rapid rise in acetyl coenzyme A carboxylase activity which occurred within minutes of biotin injection. Further evidence for the presence of apoenzyme in deficient adipose tissue came from equivalence point determinations with the use of an antibody against acetyl coenzyme A carboxylase. These experiments indicated that adipose tissue from deficient rats contains immunologically reactive but catalytically inactive protein which is presumably acetyl coenzyme A apocarboxylase. Biotin-deficient and control rats were injected with 3H-biotin, and subsequently acetyl coenzyme A carboxylase was isolated from liver and adipose tissue by immunological precipitation. There was increased 3H-biotin incorporation into deficient adipose tissue enzyme compared with control adipose tissue enzyme but only minimally increased incorporation into liver enzyme, again demonstrating the marked difference in the metabolism of the enzyme in these tissues. The conversion of acetyl coenzyme A apocarboxylase to holoenzyme was demonstrated in vitro with the use of a 105,000 x g supernatant fraction from adipose tissue of deficient animals.