Expression of the mammalian mitochondrial genome. Stability of mitochondrial translation products as a function of membrane potential.

Polypeptide decay has been measured as a function of membrane potential. Mitochondrial translation products were pulse-labeled in vitro with [35S]methionine using isolated rat heart mitochondria in the presence of an energy-generating system. The relative rate of protein degradation was estimated from the specific activity (counts/min/mg of protein) of the labeled translation products following the addition of unlabeled methionine (chase). To modulate membrane potential, inhibitors of oxidative phosphorylation were used singly or in combination; their effect was monitored by following uptake of the nonmetabolizable lipophilic cation triphenylmethylphosphonium. When the potential was dissipated, the rate of polypeptide decay increased and vice versa. These results suggest that the stability of mitochondrial translation products is linked to a process(es) that is dependent upon delta psi; likely candidates include synthesis and/or assembly of mitochondrial gene products.