This domain is found in bacteria and plant chloroplast proteins. It often appears at the C-terminal of nitrogenase component 1 type oxidoreductases (IPR000510) and sometimes independently in bacterial proteins such as the proto-chlorophyllide reductase subunit B of the cyanobacterium Synechocystis.
This domain is also associated with chlorophyllide reductase subunit Z, converts chlorophylls (Chl) into bacteriochlorophylls (BChl) by reducing ring B of the tetrapyrrole.