The turnover of the protein components of mitochondria from rat liver, kidney, and brain.

The turnover rates of the protein components of rat liver, kidney, and brain mitochondria were determined. In liver mitochondria, all protein components had an identical halflife of 8.5 days. In kidney mitochondria, the water-soluble proteins had a half-life of 5.9 days which was significantly shorter than that of the whole mitochondria, 8.6 days. The other protein components of kidney mitochondria had halflives which did not differ significantly from that of the whole mitochondria. A similar situation was obtained with brain mitochondria in which the water-soluble proteins had a half-life of 17.9 days as compared to 26.3 days for the whole mitochondria. It is of interest that these water-soluble proteins appear to be synthesized extramitochondrially and then subsequently integrated into the mitochondrial structure.