THE BIOGENESIS OF MITOCHONDRIA

Abstract

SummaryA comparison has been made of the composition and enzymic content of mitochondria isolated from Saccharomyces cerevisiae grown under varying degrees of glucose repression. An increase in the degree of repression of that whole yeast cell results in a decreased oxidative activity of the isolated mitochondria, a decrease associated with a lower content of cytochromes and decreased activities of a number of membrane‐bound dehydrogenases and citric acid cycle enzymes. The concentrations of individual cytochromes and enzymes were affected by the catabolite repression to a variable degree.The lipid content and composition of yeast mitochondria and the effects of repression on the mitochondrial lipids have also been investigated. Mitochondria from non‐repressed yeast cells, which in oxidative activity resemble mammalian mitochondria, differ from them in having a lower phospholipid and higher neutral lipid content and in containing a high proportion of mono‐unssaturated fatty acids in place of polyunsaturated fatty acids. Glucose repression selectively affects the phospholipids of the mitochondria, resulting in a reduced total phospholipid content and a more saturated pattern of the fatty acyl composition of the phospholipid.The changes in the protein and lipid composition of the mitochondria are correlated with changes in the morphology of mitochondria as shown in electron micrographs of cells grown under different degrees of repression.The results indicate that catabolite repression affects the entire organization of the yeast mitochondrion, and the wide variation in the proportions of lipid and protein components in the mitochondria suggests that the assembly of the organelle in yeast is a stepwise process.