Induction of cytochromes in human cells by oxygen

The mechanism of cytochrome induction in human cells was investigated. Cultured fibroblasts grown in low oxygen had markedly reduced contents of cytochromes A + A(3), B, and C + C(1) as measured by absorption spectra. Chloramphenicol but not cycloheximide or actinomycin blocked the initial increase in cytochrome oxidase activity in cells shifted from low to ambient oxygen, suggesting that initiation of enzyme induction requires mitochondrial but not cytoplasmic protein synthesis or transcription of nuclear genes. Turnover of cytochrome oxidase was demonstrated in cells in stationary phase.