JBC, Vol. 254, Issue 19, 9365-9368, Oct, 1979
Phosphorylation of ATP citrate lyase in response to glucagon
A. M. Janski, P. A. Srere, N. W. Cornell and R. L. Veech
Incubation of hepatocytes with [32P]orthophosphate resulted in the
incorporation of 32P into material that is precipitated by reaction with
antibodies to ATP citrate lyase. The amount of radioactivity precipitated
was decreased when unlabeled, purified ATP citrate lyase was added to
extracts of hepatocytes that had been incubated with [32P]orthophosphate.
Addition of glucagon to hepatocytes that had been preincubated with
[32P]orthophosphate resulted in a 56% increase in acid-stable 32P in the
trichloroacetic acid-insoluble portion of immunoprecipitates. Catalytic
phosphate bound to ATP citrate lyase reaction with ATP and Mg2+ is
acid-labile; thus, glucagon-dependent phosphorylation is distinguished from
the catalytic phosphate. When hepatocytes were incubated in the absence of
[32P]orthophosphate and extracted in a medium containing [gamma-32P]ATP, no
acid-stable 32P was present in immunoprecipitates. This indicates that the
incorporation into ATP citrate lyase of acid-stable phosphate occurs prior
to extraction of the enzyme. Preliminary studies, using a procedure that
allows for measurement of enzyme activity starting 1 min after beginning
the extraction of lyase from hepatocytes, have shown no difference in lyase
activity when hepatocytes are treated with or without glucagon.
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