Regulation of rat-kidney cortex fructose-1,6-bisphosphatase activity. I. Effects of fructose-2,6-bisphosphate and divalent cations

Abstract 1. 1. The native rat-kidney cortex Fructose-1,6-BPase is differentially regulated by Mg 2+ and Mn 2+ . 2. 2. Mg 2+ binding to the enzyme is hyperbolic and large concentrations of the cation are non-inhibitory. 3. 3. Mn 2+ produces a 10-fold rise in V max higher than Mg 2+ . [Mn 2+ ] 0.5 is much larger than [Mg 2+ ] 0.5 . At elevated [Mn 2+ ] inhibition is observed. 4. 4. Mg 2+ and Mn 2+ produce antagonistic effects on the inhibition of the enzyme by high substrate. 5. 5. Fru-2,6-P 2 inhibits the enzyme by rising the S 0.5 and favouring a sigmoidal kinetics. 6. 6. The inhibition by Fru-2,6-P 2 is released by Mg 2+ and more powerfully by Mn 2+ increasing the I 0.5 .