Mitochondrial Biogenesis

Formate is utilized for mitochondrial polypeptide chain initiation, and formyl label is retained as N-formylmethionine in mitochondrial proteins. Chloramphenicol inhibits this incorporation of formate into mitochondrial proteins by more than 95% demonstrating the specificity of this labeling procedure. A second product derived from formate and appearing in mitochondrial proteins is represented by serine which is formed and incorporated in the cell sap. These two products can be distinguished either after complete enzymatic hydrolysis or, on the intact protein, by the acid lability of the formyl linkage. Proteins initiated, translated, and integrated into their final membrane sites within the mitochondria may therefore be identified by the lability of their formate label. These techniques should prove valuable in determining the site of synthesis of purified protein subunits without the use of inhibitors, as well as for studying inter-compartmental regulation of polypeptide synthesis. We have examined this question and now provide evidence for tight coupling between the mitochondrial and cell sap systems. Interruption of protein synthesis on cell sap ribosomes has no effect on polypeptide chain initiation in the mitochondria, yet the elaboration of complete membrane-associated proteins stops rapidly.