PHOTOACTIVATION AND REGULATION OF SPINACH LEAF FRUCTOSE 1,6-BISPHOSPHATASE

Fructose 1,6-bisphosphatase, in isolated intact chloroplast from spina ch leaves, is photoactivated by ferredoxin/thioredoxin system. The mec hanism involved is conversion of enzyme disulfide to sulfhydryl groups as the photoactivation is inhibited by sulfhydryl group modifying age nts which are able to penetrate the chloroplast envelope. Reduction of ferredoxin on the reducing side of photosystem I is found to be a key event and active electron flow to ferredoxin must be maintained for k eeping the enzyme in activated state. DCMU - a classical electron tran sport chain inhibitor and other exogenously added electron accepters, which intercept electrons on or before ferredoxin cause deactivation o f fructose 1,B-bisphosphatase in light. The rate of deactivation, in d ark, is also enhanced by exogenously added electron accepters and sulf hydryl group modifying agents. The mechanism of regulation of fructose 1,6-bisphosphatase is discussed.