Formation of malonyl coenzyme A in rat heart. Identification and purification of an isozyme of acetyl-coenzyme A carboxylase from rat heart

Acetyl-CoA carboxylase is thought to be absent in the heart since the latter is highly catabolic and non-lipogenic. It has been suggested that the high level of malonyl-CoA that is found in the heart is derived from mitochondrial propionyl-CoA carboxylase, which also uses acetyl-CoA. In the present study, acetyl-CoA carboxylase was identified and purified from homogenates of rat heart. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the preparation from heart showed the presence of one major protein band (M sub(r) 280,000) and a minor band (M sub(r) 265,000) while that from liver gave a major protein band (M sub(r) 265,000). The observations suggest the presence of two isozymes of acetyl-CoA carboxylase that are immunologically distinct, the 265-kDa species being predominant in the liver and the 280-kDa species being predominant in the heart.