Ferric reductases in Escherichia coli: the contribution of the haemoglobin-like protein.

The haemoglobin-like protein (HMP) of E. coli previously isolated as a dihydropteridine reductase was shown to be also a ferric citrate reductase. We demonstrate that, in fact, HMP is a flavin reductase and that its ferric reductase activity is a result of its ability to reduce free flavins. However, when compared to the two main ferric/flavin reductases of E. coli, i.e., the NAD(P)H: flavin oxidoreductase and the sulfite reductase, one can conclude that the contribution of HMP to iron reduction is negligible.