Protochlorophyllide reductase
In enzymology, protochlorophyllide reductases are enzymes that catalyze the chemical reaction
The three substrates of this enzyme are protochlorophyllide, NADPH, and H+; its two products are chlorophyllide a and NADP+.
This enzyme belongs to the family of oxidoreductases. The systematic name of this enzyme class is chlorophyllide-a :NADP+ 7,8-oxidoreductase. Other names in common use include NADPH2-protochlorophyllide oxidoreductase, NADPH-protochlorophyllide oxidoreductase, NADPH-protochlorophyllide reductase, protochlorophyllide oxidoreductase, and protochlorophyllide photooxidoreductase. This enzyme is part of the biosynthetic pathway to chlorophylls.
There are two structurally unrelated proteins with this activity, referred to as light-dependent and the dark-operative. The light-dependent reductase needs light to function, while the dark-operative version is a completely different protein, consisting of three subunits that exhibit significant sequence similarity to the three subunits of nitrogenase. This enzyme might be evolutionary older but is highly sensitive to free oxygen and does not work if its concentration exceeds about 3%. Hence the alternative, light dependent version evolved as the concentration of oxygen in the earth's atmosphere grew.
