A product‐regulated fructose 2,6‐bisphosphatase occurs in green leaves

Abstract

An enzyme catalyzing the hydrolytic conversion of fructose 2,6‐bisphosphate (Fru‐2,6‐P 2 ) to fructose 6‐phosphate (Fru‐6‐P) and P i has been identified and purified from plants, specifically the cytosolic fraction of spinach leaf parenchyma cells. Partially purified preparations of the enzyme, designated fructose 2,6‐bisphosphatase (Fru‐2,6‐P 2 ase), were inhibited by products of the reaction (i.e., P i and Fru‐6‐P) but showed no response to a protein phosphorylation system known to inhibit the corresponding enzyme in mammalian cells. Fru‐2,6‐P 2 ase co‐purified with fructose 6‐phosphate,2‐kinase, the enzyme catalyzing the synthesis of Fru‐2,6‐P 2 . The observed pattern of regulation of the enzymes functional in the synthesis and breakdown of Fru‐2,6‐P 2 reinforces the conclusion that chloroplasts play a role in controlling cytosolic carbon processing in leaves.