Incorporation of labeled formate into rat liver mitochondrial proteins and initiation of protein synthesis

It was established that when rat liver mitochondria are incubated in vitro, labeled formate is incorporated into the TCA-insoluble material in the course of mitochondrial translation. From the results of hydrolysis with cyanogen bromide (at the methionine residue) with 0.5 N HCl (deformylation of N-formyl derivatives of amino acids) it follows that the formyl group of the N-terminal methione accounts for about half of the total protein radioactivity. The labeling of the growing polypeptides with formate (but not with phenylalanine or methionine) is phasic with a period of similarly ordered 13 min. The potential for initiation is unchanged and exceeds the actually observed level by more than an order of magnitude. The results obtained are an indication of the reality of the previously predicted synchronization of mitochondrial protein synthesis, the cause of which may be the stages of translation preceding the formation of the first peptide bond