InterPro: IPR008434 Magnesium-protoporphyrin IX monomethyl ester aerobic oxidative cyclase

This family represents the oxidative cyclase responsible for forming the distinctive E-ring of the chlorin ring system under aerobic conditions [1]. This enzyme is believed to utilise a binuclear iron centre and molecular oxygen. There are two isoforms of this enzyme in some plants and cyanobacteria, which are differentially regulated based on the levels of copper and oxygen [2, 3]. This step is essential in the biosynthesis of both bacteriochlorophyll and chlorophyll under aerobic conditions (a separate enzyme, BchE, acts under anaerobic conditions). This enzyme is found in plants, cyanobacteria and other photosynthetic bacteria.

CRD1 (AcsF) is required for the maintenance of photosystem I and its associated light-harvesting complexes in copper-deficient (-Cu) and oxygen-deficient (-O(2)) Chlamydomonas reinhardtii cells and is localised to the thylakoid membrane. The family also contains the Rhodocyclus gelatinosus (Rhodopseudomonas gelatinosa) AcsF protein [1].