p21 ras proteins and guanine nucleotides modulate the phosphorylation of 36- and 17-kilodalton mitochondria-associated proteins.

We have found that, when isolated rat liver mitochondria are incubated with [gamma-32P]ATP, there is phosphorylation of 36- and 17-kDa proteins. These proteins together with their protein kinase(s) are released as a complex by incubation of the isolated rat liver mitochondria at 20 degrees C for 30 min with 10 mM glucose 6-phosphate, 0.5 mM inositol phosphate, or 0.01 mM inositol triphosphate. Phosphorylation of the 36- and 17-kDa proteins in this soluble protein fraction is modulated by p21 proteins encoded by ras oncogenes and synthesized in Escherichia coli via recombinant DNA methods. A normal p21 ras protein stimulates phosphorylation of the 36-kDa protein and inhibits phosphorylation of the 17-kDa protein, whereas two transforming p21 ras proteins inhibit phosphorylation of both the 36- and 17-kDa proteins. Although GDP and 5'-guanylyl imidodiphosphate also influence the phosphorylation of these proteins, we present evidence that the effects of p21 ras protein are not simply due to their bound GDP. This novel system may be useful for further studies on the biochemical functions of the p21 ras proteins.