MITOCHONDRIAL CYTOCHROME CONTENT AND CYTOCHROME-OXIDASE ACTIVITY OF SOME AMAZONIAN FISH

1. 1. The cytochrome content of Keilin-Hartree particles isolated from water-breathing and facultative air-breathing fishes is reported and compared with data for mammalian mitochondria. 2. 2. Steady-state kinetic measurements were performed on the oxidase system. The results may be interpreted in terms of two, kinetically significant cytochrome c binding sites associated with cytochrome oxidase with Km values of ∼ 1 × 10-6 and ∼5 × 10-8 M. These values are close to those reported for beef mitochondria (Ferguson-Miller et al., 1976). 3. 3. The turnover numbers for the cytochrome oxidases from a variety of fishes are compared, and are found to be similar and close to the value found for the mammalian enzyme. 4. 4. The constancy of the cytochrome content and the kinetic parameters from species to species suggests that the cellular respiratory processes constitute a conservative system from the standpoint of evolution. © 1979.