DEPENDENCE OF MITOCHONDRIAL PROTEIN-SYNTHESIS INITIATION ON FORMYLATION OF INITIATOR METHIONYL-TRANSFER-RNAF

  • 1 January 1977
    • journal article
    • research article
    • Vol. 252  (8) , 2519-2523
Abstract
The effect of N10-formyl-H4folate on mitochondrial peptide chain initiation was studied in isolated mitochondria of Saccharomyces cerevisiae. The addition of N10-formyl-H4folate strongly stimulated the incorporation of amino acids into mitochondrial protein at 6 and 15 mM Mg2+. Still higher stimulation (up to 10-fold) was obtained in the production of de novo synthesized initial peptides, measured as peptidyl puromycin derivatives. The maximum effect is observed at 0.1 mM N10-formyl-H4folate. At 5 mM puromycin, the ratio formylated/unformylated peptides is 3, as shown by electrophoretic analysis. At 10 mM puromycin, the ratio is increased to more than 6. This is due to the presence of deformylase and amidohydrolase activities, which are more effective the longer the initial peptide is synthesized; at increasing puromycin concentrations, progressively shorter peptide chains are formed. Chemically synthesized fMet-puromycin and Met-puromycin are virtually stable when incubated with intact or frozen and thawed mitochondria. More careful kinetic analysis shows an early cessation of the initial peptide formation in the samples without N10-formyl-H4folate. This indicates that the formylation of methionyl-tRNA formylatable species is an absolute requirement for mitochondrial peptide chain initiation.

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