Abstract
AbstractIsolated rat liver hepatocytes exhibited a twofold to threefold increase in both specific cytochrome oxidase activity and heme a concentration during their first 24 h in monolayer culture. Other mitochondrial respiratory enzyme activity did not increase over this same period. Decreasing the oxygen content of the gas phase to 5% of ambient eliminated the stimulation in heme a content without having an effect on cell protein synthesis or viability. These results indicate that oxygen concentration can effect the level of cytochrome oxidase (heme a) in these differentiated cells. The effect of oxygen may be on the translation or assembly of subunits, synthesis of heme, or incorporation of heme into holoenzyme. Oxygen stimulation of cytochrome oxidase content was not accompanied by increased incorporation of pulsed radiolabelled methionine into immunoprecipitated holoenzyme subunits. Moreover, chloramphenicol, a translation inhibitor of three mitochondrially synthesized cytochrome oxidase subunits, did not diminish the increase in heme a seen over the first 24 h of culture. These latter results suggest that the increasing enzyme content is not due to stimulated translation.
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