The Journal of Cell Biology, Vol 98, 2174-2178, Copyright © 1984 by The Rockefeller University Press
Cyclic AMP-dependent phosphorylation of the precursor to beta subunit of mitochondrial F1-ATPase: a physiological mistake?
RA Steinberg
By using the purified rat liver protein for reference in electrophoresis
and peptide mapping experiments, I have identified the beta subunit of
mitochondrial F1-ATPase and its cytoplasmic precursor in two-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. This suggests that phosphorylated
beta subunit is recognized as aberrant and excluded from assembly into the
ATPase complex. These results argue that cAMP-dependent phosphorylation of
the beta subunit precursor is a physiological mistake that is remedied
after mitochondrial import and processing.
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