The incorporation of radioactive amino acids and of delta-amino[2,3-(3)H(2)]laevulinate into rat liver cytochromes b(5) and c and cytochrome oxidase has been examined with and without protein-synthesis inhibitors. Cycloheximide promptly inhibits labelling of both haem and protein for cytochrome c in parallel fashion. Although incorporation of (14)C-labelled amino acid into microsomal cytochrome b(5) is also rapidly inhibited, cycloheximide incompletely inhibits haem labelling of cytochrome b(5) and cytochrome a+a(3), and inhibition occurs only after repeated antibiotic injections. The possibility of apo-protein pools, or of haem exchange, with a rapidly renewed ;free' haem pool, is considered. Consistent with this model is the observation of non-enzymic haem exchange in vitro between cytochrome b(5) and methaemoglobin. Chloramphenicol, injected intravenously over 5h, results in a 20-40% decrease in incorporation of delta-amino[2,3-(3)H(2)]laevulinate into haem a+a(3) and haem of cytochromes b(5) and c. With the dosage schedule of chloramphenicol studied, amino acid labelling of total liver protein and of cytochrome c was not inhibited. Similarly, ferrochelatase activity was not decreased.

Journal Article↗

PubMed1973

Synthesis and degradation of mitochondrial components in hypertrophied rat heart.

The accumulation of inner mitochondrial components of rat heart was studied 1 and 3 days after constriction of the ascending aorta of rats. By 1 day after aortic constriction, the activities of three mitochondrial respiratory enzymes/mg of cardiac homogenate protein were increased; after 3 days, specific activities had levelled off or decreased. Selective accumulation of inner mitochondrial membrane components 24h after aortic constriction was further indicated by increased left ventricular cytochrome c concentration (nmol/mg of protein). By 3 days after surgery, cytochrome c concentration was significantly diminished. Low-temperature spectroscopy of isolated mitochondria showed that the ratios of cytochromes c, b and a+a(3) remained unchanged after aortic constriction, suggesting that cytochrome c was a good indicator of the response of the other mitochondrial inner-membrane cytochromes as well. The effect of cardiac hypertrophy on the turnover of cytochrome c was also examined. Cytochrome c was labelled in its haem group with delta-amino[2,3-(3)H(2)]laevulinate 3 days before aortic constriction. By 1 day after surgery the total ventricular radioactivity in cytochrome c of aortic banded animals was significantly higher than in sham-operated controls, indicating a decreased degradation rate in the former during the first postoperative day. delta-Aminolaevulinate was shown to be a particularly suitable precursor for such turnover studies, since it results in rapid pulse-labelling of cytochrome c (peak activity in 90min), is rapidly removed from the precursor pool (t((1/2))=30min) and is not reutilized.

Animals↗

PubMed1973