CYTOCHROME-C-OXIDASE IN DEVELOPING RAT-HEART - ENZYMATIC-PROPERTIES AND AMINO-TERMINAL SEQUENCES SUGGEST IDENTITY OF THE FETAL HEART AND THE ADULT LIVER ISOFORM

Perinatal development of cytochrome-c oxidase (complex IV) and ubiquin ol - cytochrome-c reductase (complex III) was investigated in rat hear t and liver by analysing catalytic properties, protein amounts, and su bunit isoforms during the transition from the fetal to the adult state . The total amounts of complexes from milligram quantities of tissue, and the portions of isoforms of complex IV, were quantified densitomet rically after isolation of the native complexes by blue native polyacr ylamide gel electrophoresis and separation of the protein subunits by Tricine/SDS/PAGE [Schagger, H. and von Jagow, G. (1991) Anal. Biochem. 198, 223-231]. A parallel increase of protein amounts and catalytic a ctivities during perinatal development was observed in heart and liver for complex III, but only in liver for complex IV. In heart, both a d oubling of the turnover number of complex IV and a lowered K-m for cyt ochrome c were observed. The altered enzymic properties correlated wit h the increase of heart type subunits VIa and VIII. The fetal enzymes from heart and liver seem to be identical to the adult liver isoform, as deduced from their enzymic properties and identical aminoterminal s equences of subunits VIa and VIII.