Cyclic AMP-dependent phosphorylation of the precursor to beta subunit of mitochondrial F1-ATPase: a physiological mistake?

Abstract

By using the purified rat liver protein for reference in electrophoresis and peptide mapping experiments, the .beta. subunit of mitochondrial F1-ATPase and its cytoplasmic precursor were identified in 2-dimensional gel patterns of proteins from S49 mouse lymphoma cells. The .beta. subunit precursor is a substrate for cAMP-dependent phosphorylation during its synthesis. Normally, both nonphosphorylated and phosphorylated forms of .beta. subunit precursor are processed rapidly to the smaller, more acidic forms of mature .beta. subunit. When processing is inhibited with valinomycin, both nonphosphorylated and phosphorylated forms of .beta. subunit precursor are stabilized. Nonphosphorylated .beta. subunit is one of the most stable of cellular proteins, but the phosphorylated form is eliminated within minutes of processing. Phosphorylated .beta. subunit is probably recognized as aberrant and excluded from assembly into the ATPase complex. These results argue that cAMP-dependent phosphylation of the .beta. subunit precursor is a physiological mistake that is remedied after mitochondrial import and processing.