Chlorophyllide a reductase

Chlorophyllide a reductase (EC 1.3.7.15), also known as COR, is an enzyme with systematic name bacteriochlorophyllide-a:ferredoxin 7,8-oxidoreductase.[1][2] It catalyses the following chemical reaction

chlorophyllide a + 2 reduced ferredoxin + ATP + H₂O + 2 H⁺ ${\displaystyle \rightleftharpoons }$ 3-deacetyl 3-vinylbacteriochlorophyllide a + 2 oxidized ferredoxin + ADP + phosphate

• Structure of the substrate and product of the enzyme
• 
  Chlorophyllide a
• 
  Bacteriochlorophyllide a (R=H). The product of COR retains the vinyl group of the substrate in place of the acetyl group shown

This reduction (with trans stereochemistry) of the pyrrole ring B, gives the characteristic 18-electron aromatic system that distinguishes bacteriochlorophylls from chlorophylls, which retain the chlorin system of Chlorophyllide a. 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.[3][4][5]