VARIATIONS IN THE SUBUNIT CONTENT AND CATALYTIC ACTIVITY OF THE CYTOCHROME-C-OXIDASE COMPLEX FROM DIFFERENT TISSUES AND DIFFERENT CARDIAC COMPARTMENTS

The composition and activity of cytochrome c oxidase (COX) was studied in mitochondria from rat liver, brain, kidney and heart and also in d ifferent compartments of the bovine heart to see whether any correlati on exists between known oxidative capacity and COX activity. Immunoblo t analysis showed that the levels of ubiquitously expressed subunits I V and Vb are about 8-12-fold lower in liver mitochondria as compared t o the heart, kidney and brain. The heart enzyme with higher abundance of COX IV and Vb showed lower turnover number (495) while the liver en zyme with lower abundance of these subunits exhibited higher turnover number of 750. In support of the immunoblot results, immunohistochemic al analysis of heart and kidney tissue sections showed an intense stai ning with the COX Vb antibody as compared to the liver sections. COX V b antibody stained certain tubular regions of the kidney more intensel y than the other regions suggesting region specific variation in the s ubunit level. Bovine heart compartments showed variation in subunit le vels and also differed in the kinetic parameters of COX. The right atr ium contained relatively more Vb protein, while the left ventricle con tained higher level of subunit VIa. COX from both the ventricles showe d high K-m for cytochrome c (23-37 mu M) as compared to the atrial COX (K-m 8-15 mu M). These results suggest a correlation between tissue s pecific oxidative capacity/work load and changes in subunit compositio n and associated changes in the activity of COX complex. More importan t, our results suggest variations based on the oxidative load of cell types within a tissue. (C) 1998 Elsevier Science B.V.