Protein phosphorylation/dephosphorylation in the inner membrane of potato tuber mitochondria

Inside-out inner mitochondrial membranes free of matrix proteins mere isola ted from purified potato tuber (Solanum tuberosum L,) mitochondria and incu bated with [gamma-P-32]ATP, Proteins were separated by SDS-PAGE and visuali zed by autoradiography. Phosphorylation of inner membrane proteins, includi ng ATPase subunits, was strongly inhibited by the phosphoprotein phosphatas e inhibitor NaF. We propose that an inner membrane phosphoprotein phosphata se is required for activation of the inner membrane protein kinase, When pr elabelled inner membranes were incubated in the absence of [gamma-P-32]ATP, there was no phosphoprotein dephosphorylation unless a soluble matrix frac tion was added, This dephosphorylation was inhibited by NaF, but not by oka daic acid. We conclude that the mitochondrial matrix contains a phosphoprot ein phosphatase that is responsible for dephosphorylation of inner membrane phosphoproteins. (C) 2000 Federation of European Biochemical Societies. Pu blished by Elsevier Science B.V, All rights reserved.