Synthesis of cytochrome oxidase components in isolated mitochondria of Neurosora crassa.

The formation of polypeptides within the mitochondrion has been documented by a large body of evidence. The ability of isolated mitochondria to incorporate amino acids into membrane protein is an expression of this cellular capacity (for reviews see [ l-61 ). However, until now it has not been demonstrated that isolated mitochondria are able to synthesize definite polypeptides which are components of mitochondrial membrane enzymes. In this communication we report that isolated mitochondria of Neurospora crassa under appropriate conditions do synthesize definite polypeptides which can be shown to be components of cytochrome oxidase. As described by several laboratories, this enzyme consists of seven subunits, three of which are made by mitochondrial ribosomes, and four of which are made by cytoplasmic ribosomes [7-91. The components of cytochrome oxidase produced in isolated mitochondria were compared to the components produced in whole cells. The enzyme components were isolated by means of immunoprecipitation. It was found that the same components are made in vitro and in vivo in the presence of cycloheximide. A partial assembly of newly made cytochrome oxidase components in isolated mitochondria is discussed.