This family consists of the PetM family of cytochrome b6f complex subunit IV. The cytochrome b6f complex consists of 7 subunits and contains 2 beta hemes and 1 chlorophyll alpha per cytochrome f. It is highly active in transferring electrons from decylplastoquinol to oxidised plastocyanin [1].

1: Purification and characterization of the cytochrome b6 f complex from Chlamydomonas reinhardtii. Pierre Y, Breyton C, Kramer D, Popot JL; J Biol Chem 1995;270:29342-29349. PMID:7493968