The characterization of mitochondrial translation products in rat liver and rat hepatoma cells

Abstract

1. Introduction The mitochondrial translation products of yeast and fungi are well documented (reviews [ 1,2]). Some of the proteins synthesized in mitochondria of higher eukaryotic cells have also been identified as compo- nents of mitochondrial ATPase complex [3-5] and cytochrome oxidase [3,6-l 01. However, the use of various organisms and cells, different methods of labeling and identification of products of mitochon- drial protein synthesis resulted in some confusion as to the number, molecular weights (or M,) and func- tions of these products. Here, we have undertaken a detailed investigation of the mitochondrial translation products labeled in in vitro isolated cells and mitochondria. Two cell types were used: the rat hepatocytes and Zajdela hepatoma derived from rats. Mitochondrial transla- tion products of the cytochrome b-cl complex, cytochrome oxidase, and the ATPase complex were identified by immunological means. This study pro- vides so far the most detailed analysis of mitochon- drial translation products of higher eukaryotic cells. 2. Materials and methods Rat hepatocytes were prepared from 150-l 80 g male Sprague-Dawley rats as in [ 1 l] with some modi- fications [ 121. The maintenance, propagation and har- vesting of Zajdela hepatoma cells and the isolation of mitochondria from the tumor and rat liver were done as in [ 131 with the exception that the preparation of mitochondria from small amounts of isolated cells were performed according to [ 121.