Regulation of fructose 2,6-bisphosphate concentration in spinach leaves

Abstract

Fructose‐6‐phosphate 2‐kinase and fructose‐2,6‐bisphosphatase have been partially purified from spinach leaves and their regulatory properties studied. Fructose‐6‐phosphate 2‐kinase was activated by phosphate and fructose 6‐phosphate, and inhibited by 3‐phosphoglycerate and dihydroxyacetone phosphate. Fructose‐2,6‐bisphosphatase was inhibited by fructose 6‐phosphate and phosphate. The interaction between these effectors was studied when they were varied, alone or in combination, over a range of concentrations representative of those in thecytosol of spinach leaf cells. In conditions when dihydroxyacetone phosphate or 3‐phosphoglycerate rise, as is typical during photosynthesis, the fructose 2,6‐bisphosphate level will decrease, which will favour sucrose synthesis. In conditions when fructose 6‐phosphate accumulates, fructose 2,6‐bisphosphate should rise, which will favour a restriction of sucrose synthesis and promotion of starch synthesis.