JBC, Vol. 254, Issue 13, 5584-5587, Jul, 1979
Hormone-stimulated phosphorylation of liver phosphofructokinase in vivo
T. Kagimoto and K. Uyeda
The effect of glucagon on the phosphorylation and the enzymic activity of
phosphofructokinase in rat liver in vivo was investigated. Glucagon
stimulated the phosphorylation of liver phosphofructokinase approximately
3- to 5-fold and increased cAMP levels 5-fold and blood glucose levels
2-fold over the values obtained for control animals. The specific
radioactivity of ATP isolated from liver was the same in both control and
hormone-treated animals. During the purification of the 32P-labeled enzyme
from both animals, no difference was observed in the total or specific
enzyme activities of the enzymes from the various fractions. Thus,
phosphofructokinase appears to be phosphorylated in vivo by a cyclic
AMP-dependent protein kinase. Although phosphorylation does not affect the
maximum catalytic activity of the enzyme, it does render the enzyme
significantly more sensitive to ATP inhibition. Thus, at a given
concentration of ATP, the phosphorylated phosphofructokinase exhibits
considerably lower activity than the unphosphorylated enzyme. The possible
relationship between our observations and glucagon-mediated control of
glycolysis is discussed.
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