Phosphorylation of a Low-Molecular-Weight Polypeptide in Rat Liver Mitochondria and Dependence of Its Phosphorylation on Mitochondrial Functional State

T. S. Azarashvili^*, I. V. Odinokova, and Yu. V. Evtodienko

Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia; E-mail: azarashvili@venus.iteb.serpukhov.su

^* To whom correspondence should be addressed.

Received June 11, 1998; Revision received December 20, 1998

---

We show that incubation of rat liver mitochondria in the presence of [gamma-³²P]ATP results in cAMP-dependent phosphorylation of a low-molecular-weight (3.5-kD) polypeptide (LMWP). This component is tightly bound to the mitochondrial membrane. It is not released into solution after freezing and subsequent thawing of the mitochondrial suspension and does not incorporate ³²P from [gamma-³²P]ATP in the presence of uncouplers of oxidative phosphorylation. Inhibition of adenine nucleotide transport into the mitochondrial matrix by carboxyatractyloside suppresses phosphorylation of the LMWP. Moderate Ca²⁺ loading of mitochondria increases both phosphorylation and dephosphorylation of the LMWP. Chelation of Ca²⁺ by incubation in the presence of EGTA suppresses incorporation of ³²P into the LMWP.

---

KEY WORDS: mitochondria, protein phosphorylation, protein kinases, calcium transport

---