J. Biol. Chem., Vol. 265, Issue 13, 7532-7538, May, 1990
Expression of the mammalian mitochondrial genome. Role for membrane potential in the production of mature translation products
C Cote, D Boulet and J Poirier
Department of Chemistry, Universite du Quebec a Montreal, Canada.
Protein synthesis was investigated in isolated mitochondria under
conditions which either inhibited electron transport or uncoupled oxidative
phosphorylation. In a medium containing an exogenous source of ATP and
oligomycin, an inhibitor of the ATP synthase complex, incorporation of
[35S]methionine into proteins is stimulated in the presence of inhibitors
of the electron transport chain; substituting uncouplers of oxidative
phosphorylation for the latter leads, in contrast, to a decrease in the
rate of incorporation of the labeled amino acid into mitochondrial
translation products. Studies on the metabolic stability of mitochondrial
translation products revealed that "mature" polypeptides made in isolated
mitochondria are stable as indicated by the absence of degradation during a
50 min "chase" period. Under conditions which reduce or dissipate the
membrane potential, 50- 60% of the newly made polypeptides (pulse) are
degraded within 50 min. The kinetics of the degradation process for
individual mitochondrial gene products reveal that the largest proportion
of polypeptides degraded to an acid-soluble form during the chase period
are abnormal proteins, likely the result of premature chain termination.
Emerging as a common denominator in these studies is a role for a
transmembrane potential across the inner membrane in the production of
mature "stable" mitochondrial gene products.