Required for correct biomineralization of the magnetosome; probably converts and then transports some form of iron. It is partially functionally redundant with MamH (PubMed:23889511). May function with MamX, MamY amd Mms6 in biomineralization (Probable). Despite its strong similarity to MsrQ (AC V6EX82) this protein does not genetically interact with bona fide MsrP (AC V6F0A4), which is encoded elsewhere in the genome (PubMed:23889511). Probably interacts with FtsZ-like and MamY proteins. Expressed in exponential phase, peaks about 18 hours. The most highly expressed gene in this operon (PubMed:20023033, PubMed:24020498). Protein is associated with magnetosomes at mid-development then decreases (at protein level) (PubMed:30367002). Third gene in the 4 gene mamXY operon (PubMed:20023033) (Probable). Deletion of the C-terminal 'ferric reductase' domain (residues 444-645) phenocopies the deletion mutant; makes a magnetosome with normal crystals sandwiched between flake-like crystals. Slightly reduced magnetic response, produces chains of wild-type magnetite crystals sandwiched between irregularly shaped, small flake-like crystals. The flake-like crystals are hematite not magnetite. Phenotype is exacerbated when grown in NH(4)(+) instead of NO(3)(-) medium. Double mamH-mamZ deletion cells have a poor magnetic response and very few wild-type crystals; most cells have flake-like crystals (PubMed:23889511). Deletion of 4 consecutive genes (mamY, mamX, mamZ, ftsZm) leads to cells with an intermediate magnetic response where magnetosomes have short chains of nearly regularly shaped, cubo-octahedral crystals flanked by small particles with poorly defined morphologies (PubMed:22043287). This bacteria makes up to 60 cubo-octahedral magnetosomes of about 45 nm in diameter which contain membrane-bound crystals of magnetite (Fe(3)O(4)). In the N-terminal section; belongs to the major facilitator superfamily. It is uncertain whether Met-1 or Met-6 is the initiator.