Heterogeneous photochemical and chloroplasts mediated activation of spinach fructose-1,6-bisphosphatase

A heterogeneous photochemical electron relay system was constructed, mimicking the chloroplast electron transport reaction, in order to activate fructose-1,6-bisphosphatase in light. The photocatalyst acridine orange or proflavin sensitizes EDTA dependent reduction of ferredoxin. In a complete system, consisting of a dye-donor couple, ferredoxin, thioredoxin and ferredoxin-thioredoxin reductase, light activation of purified spinach fructose-1,6-bisphosphatase was observed in vitro. The ferredoxin was not essential for activation of fructose-1,6-bisphosphatase using heterogeneous photochemical system while chloroplasts mediated redox activation essentially required ferredoxin. The heterogeneous photochemical system activated fructose-1,6-bisphosphatase by about 6 fold similar to chloroplasts mediated ferredoxin dependent redox activation. These observations suggest that a thiol mediator is essential for the reductive activation of carboxylating enzymes of photosynthesis. The mechanism of activation is discussed.