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Fructose 2,6-Bisphosphate and Enzymatic Activities for Its Metabolism in Ascites Tumor

1985; Academic Press; Linguagem: Inglês

10.1016/b978-0-12-152827-0.50042-6

0070-2137

LISARDO BISCÁ, Juan J. Aragón, Alberto Sols,

Diet, Metabolism, and Disease

Fructose 2,6-bisphosphate (fructose-2,6-P2) is a potent activator of the isozyme of phosphofructokinase present in ascites tumors, and in tumors of liver and muscle. The system is likely to be significant in the maintenance of the high rate of tumor glycolysis. When fructose-2,6-P2 is measured in tumor cells immediately frozen in liquid nitrogen after being withdrawn from the abdominal cavity of the animal, the content of this metabolite is evaluated to be 3.9 ± 1.0 nmol/g fresh weight, which is three times greater than the value obtained in washed cells preincubated for 30 minutes in the absence of glucose. This difference may be because of the depletion of endogenous hexose monophosphates during the preincubation period. Incubation of the enzyme preparation with the catalytic subunit of cAMP-dependent protein kinase in the presence of Mg-ATP leads to a 10-fold decrease in 6-phosphofructo-2-kinase activity and to a twofold increase in fructose-2,6-bisphosphatase activity. This suggests that fructose-2,6-P2 levels in ascites tumor can be potentially affected by phosphorylation of the kinase phosphatase by cAMP-dependent protein kinase. Nevertheless, the activity of cAMP-dependent protein kinase in ascites tumor at 2 μM cAMP is only 0.25 nmol 32Pi/min-g cells, which represents about one fifth of the activity measured in a liver extract.