Chlorophyllide a reductase
Chlorophyllide a reductase, also known as COR, is an enzyme with systematic name bacteriochlorophyllide-a:ferredoxin 7,8-oxidoreductase. It catalyses the following chemical reaction
This reduction, of the sidechains in the pyrrole ring, gives the characteristic 18-electron aromatic system that distinguishes bacteriochlorophylls from chlorophylls, which retain the chlorin system of chlorophyllide a. The enzyme uses ferredoxin and adenosine triphosphate as cofactors and gives adenosine diphosphate and phosphate as byproducts.
This enzyme is present in purple bacteria such as Rhodobacter capsulatus and Rhodobacter sphaeroides, and Pseudomonadota. It is a component of the biosynthetic pathway to bacteriochlorophylls.