IDENTIFICATION OF TISSUE-SPECIFIC ISOFORMS FOR SUBUNITS VB AND VIIA OF CYTOCHROME-C-OXIDASE ISOLATED FROM RAINBOW-TROUT

Cytochrome c oxidase was isolated from heart and liver of rainbow trout (Salmo gairdnerii). SDS/PAGE analysis showed the presence of 11 different polypeptide subunits in the fish enzyme. The nuclear-coded subunits TV, Va, Vb, VIc, VIIa, VIIc and VIII could be identified by their N-terminal amino acid sequences. The mammalian subunits VIa and VIlb appear to be absent (or blocked at the N-terminal) in cytochrome c oxidase from trout. For subunit Vb, two polypeptides of different electrophoretic mobilities were found which differed in their N-terminal sequences, and represent a new pair of cytochrome-c-oxidase subunit isoforms, not found in mammalia. Both isoforms of subunit Vb were found in cytochrome c oxidase from heart and liver, but at different ratios. Subunit VIIa also seemed to occur in different isoforms, whereas subunit VIII had the same N-terminal amino acid sequence in cytochrome c oxidase of liver and heart, similar to the human-type subunit but different from rat, bovine and chicken.