Unequivocal Demonstration of Fructose-1,6-bisphosphatase in Mammalian Brain

Fructose-1,6-bisphosphatase (D-fructose-1,6-bisphosphate 1-phosphohydrolase; EC 3.1.3.11) has been found in rat brain and identified unequivocally. The enzyme has been purified to 95% homogeneity by standard procedures, including adsorption to a phosphocellulose column followed by elution with substrate. The purified enzyme exhibits a broad optimum above pH 7.6. Both fructose 1,6-bisphosphate and sedoheptulose 1,7-bisphosphate are substrates of this enzyme; the hydrolysis of the latter occurs at about 20% of the rate of the former, and the Kmfor fructose 1,6-bisphosphate is approximately 1.32 × 10-4M. 5′-AMP, an inhibitor of other mammalian-fructose-1,6-bisphosphatases, is without effect, and in further contrast with the other enzymes there is no metal requirement for activity. Purified brain enzyme fails to crossreact with the antibody prepared against the purified liver fructose-1,6-bisphosphatase. On the other hand, antiserum produced against the brain fructose-1,6-bisphosphatase quantitatively precipitates the enzyme activity and forms precipitin bands with preparations of brain fructose-1,6-bisphosphatase.