Regulatory properties of Rana esculenta liver D-fructose-1,6-bisphosphate 1-phosphohydrolase and their comparison with properties of other vertebrate liver isoenzymes

摘要

D-Fructose-1,6-bisphosphate 1-phosphohydrolase [EC 3.1.3.11] (Fru-1,6P sub(2)ase), a regulatory enzyme of gluconeogenesis, was isolated from Rana esculenta liver in homogeneous form with approximately 30% yield. Basic kinetic properties of the enzyme and its subunit molecular weight were determined. K sub(m) is 1.72 mu M. Like other vertebrate Fru-1,6P sub(2)ase, the frog liver enzyme is inhibited by fructose-2,6-bisphosphate (Fru-2,6P sub(2)) competitively, K sub(i) is 78 nM and by AMP allosterically, I sub(0.5) is 10.9 mu M. Both inhibitors (Fru-2,6P sub(2) and AMP) act synergistically on liver Fru-1,6-P sub(2)ase. K sub(i) for Fru-2,6P sub(2) determined in the presence of 1-10 mu M of AMP were 35-2 nM, respectively. Maximum activity was found at pH 7.5. Like other Fru-1,6P sub(2)ases, the frog enzyme requires magnesium ions for its activity and is activated by potassium ions; the K sub(a) for Mg super(2+) is 267 mu M, K sub(a) for K super(+) is 77 mM. The subunit molecular weight of the frog liver Fru-1,6P sub(2)ase was 37 300 Da. A great similarity between regulatory properties of frog liver Fru-1,6P sub(2)ase and liver enzymes of other vertebrates, suggests a similar regulation of gluconeogenesis in amphibia and other vertebrates.