Different isozymes of cytochrome c oxidase are expressed in bovine smooth muscle and skeletal or heart muscle.

Cytochrome c oxidase (COX) was isolated from bovine smooth muscle (rumen), and compared with the enzyme from bovine liver, heart and skeletal muscle. A new isozyme of COX was found to be expressed in smooth muscle, which differs from the isozyme in liver and heart or skeletal muscle. SDS-PAGE as well as N-terminal amino acid sequencing of separated subunits from gel bands revealed the expression of the liver isoforms for subunits VIa and VIII and of the heart isoform for subunits VIIa in COX from smooth muscle.