Pchlide_reductase_B: B protein of the NB protein complex of Protochlorophyllide (Pchlide)_reductase. Pchlide reductase catalyzes the reductive formation of chlorophyllide (chlide) from protochlorophyllide (pchlide) during biosynthesis of chlorophylls and bacteriochlorophylls. This group contains both the light-independent Pchlide reductase (DPOR) and light-dependent Pchlide reductase (LPOR). Angiosperms contain only LPOR, cyanobacteria, algae and gymnosperms contain both DPOR and LPOR, primitive anoxygenic photosynthetic bacteria contain only DPOR. NB is structurally similar to the FeMo protein of nitrogenase, forming an N2B2 heterotetramer. N and B are homologous to the FeMo alpha and beta subunits respectively. Also in common with nitrogenase in vitro DPOR activity requires ATP hydrolysis and dithoionite or ferredoxin as electron donor. The NB protein complex may serve as a catalytic site for Pchlide reduction similar to MoFe for nitrogen reduction.
Jiyao W et al.(2023). "The conserved domain database in 2023.",