Physical state of the mitochondrial inner membrane as a factor controlling the proteolysis of mitochondrial translation products in yeast.

The degradation of mitochondrial translation products has been studied in Saccharomyces cerevisiae yeast. A high rate of degradation is observed in the early exponential phase of aerobic growth. Maturation of the yeast and glucose repression suppress the degradation. Anaerobic growth is also marked by a low breakdown rate of mitochondrial translation products. These variations did not correlate with the cytochrome c hydrolase activity of sonic submitochondrial particles (this activity was shown to reflect the general state of the proteolytic system of the inner mitochondrial membrane that is responsible for the breakdown of mitochondrially made polypeptides; see Novikova, L.A., et al. (1981) FEBS Lett. 135, 245-248). Experiments with lipid-soluble paramagnetic probes revealed significant variations in the physical state of the mitochondrial inner membrane, as judged from the comparison of the temperature-dependence plots of structural parameters obtained from the EPR spectra of the probes. The breakdown of mitochondrial translation products was, in general, the more rapid the lower was the temperature of the structural transition in the mitochondrial inner membrane and the higher was the relative content of unsaturated fatty acyl chains in the membrane phospholipids.