REGULATION OF RAT-KIDNEY CORTEX FRUCTOSE-1,6-BISPHOSPHATASE ACTIVITY .1. EFFECTS OF FRUCTOSE-2,6-BISPHOSPHATE AND DIVALENT-CATIONS

1. The native rat-kidney cortex Fructose-1,6-BPase is differentially r egulated by Mg2+ and Mn2+. 2. Mg2+ binding to the enzyme is hyperbolic and large concentrations of the cation are non-inhibitory. 3. Mn2+ pr oduces a 10-fold rise in V-max higher than Mg2+. [Mg-2+](0.5) is much larger than [Mg2+](0.5). At elevated [Mn2+] inhibition is observed. 4. Mg2+ and Mn2+ produce antagonistic effects on the inhibition of the e nzyme by high substrate. 5. Fru-2,6-P-2, inhibits the enzyme by rising the S-0.5 and favouring a sigmoidal kinetics. 6. The inhibition by Fr u-2,6-P-2 is released by Mg2+ and more powerfully by Mn2+ increasing t he I-0.5.