Turnover of outer and inner membrane proteins of rat liver mitochondria

Recent reports on the properties and composition of outer and inner mitochondrial membranes suggest that outer and inner membranes of mitochondria are derived from different sources of the cell [l-3]. In vitro experiments [4-61 indicate that the protein synthesizing system of isolated rat liver mitochondria contributes only to the synthesis of the inner and not to that of the outer mitochondrial membrane. From these findings it seemed possible that a difference in the biogenetic origin of outer and inner mitochondrial membrane might be reflected in the turnover of these mitochondrial components. The question whether all components of the mitochondrion turn over at the same half life has already been raised by Fletcher and Sanadi [7]. These authors concluded from their data that the mitochondrion turns over as an entity. More recently Bailey et al. [8] have shown evidence for the presence of mitochondrial phospholipid components with large differences in half life. Data presented in this paper indicate a half life of mitochondrial outer membrane proteins (4.2 f 1 .l days) which significantly differs from the half life of the inner membrane proteins (12.6 + 1.3 days).