Fig. 1.

Heme efflux systems of C. diphtheriae and L. lactis [56,57]. (A) In C. diphtheriae, cytoplasmic membrane ChrS senses heme and autophosphorylation occurs. The phosphate group is transferred to ChrA such that phosphorylation ensues. ChrA binds the DNA sequence within the promoter of hrtAB, thereby activating the expression of hrtA and hrtB and resulting in the extrusion of heme via the HrtAB efflux pump. P* represents the phosphate group. (B) In L. lactis, the regulator HrtR binds to heme and alleviates the inhibition on the hrtAB promoter, leading to the extrusion of heme by HrtAB.