Photoreduction of NAD and NADP by chlorophyllin a in the presence of ascorbate: Requirement for NADP reductase☆

Add time:09/04/2019    Source:sciencedirect.com

Chlorophyllin a catalyzes the photoreduction of NADP (and NAD to a lesser extent) in the presence of ascorbate as electron donor and NADP reductase as the coupling enzyme. Photosynthetic pyridine nucleotide reductase is inactive in the reaction and does not stimulate the reaction observed with NADP reductase. The presence of deoxycholate (0.6%) and methanol (30%) serves to stimulate markedly the NADP reaction, with rates as high as 615 μmoles reduced per hour per μmole chlorophyllin being observed in their presence. Removal of magnesium somewhat increases the activity of chlorophyllin a for this reaction. An aggregated form of chlorophyllin a, which is retained by a dialysis membrane, is the most active form for the photocatalyst. The reaction does not saturate at light intensities up to 20,000 foot candles, proceeds best under anaerobic conditions, and is inhibited by the addition of phenazine methosulfate, 2,6-dichlorophenolindophenol or reduced trimethyl benzoquinone. The reaction is a Krasnovsky-type reaction in which the activated chlorophyll couples with the enzyme NADP reductase to transfer electrons to NADP from ascorbate.

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