Photoactivation of NADP-malate dehydrogenase by a heterogeneous photochemical system in Zea mays

A heterogeneous photochemical electron relay system was constructed, mimicking the chloroplast electron transport reaction in order to activate the NADP-malate dehydrogenase in light, The photocatalyst acridine orange or proflavin sensitized 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 NADP-MDH was observed in vitro. The chloroplast mediated redox activation of enzyme essentially required ferredoxin, while heterogeneous photochemical mediated activation of enzyme need not require ferredoxin. The heterogeneus photochemical system activated NADP-MDH by eight fold similar to chloroplasts mediated ferredoxin dependent redox activation but was not affected by the presence of disalicylinden propanediamine-1, 2-disulphonic acid while there was complete inhibition of chloroplasts mediated activation of NADP-MDH in presence of this inhibitor. These observations suggest that a thiol mediator is essential for reductive activation of NADP-MDH and ferredoxin is not required for photochemical activation.