The affinity of MhuD for heme is consistent with a heme degrading function in vivo

MhuD is a protein found in mycobacteria that can bind up to two heme molecules per protein monomer and catalyze the degradation of heme to mycobilin in vitro. Here the Kd1 for heme dissociation from heme-bound MhuD was determined to be 7.6 ± 0.8 nM and the Kd2 for heme dissocation from diheme-bound MhuD was determined to be 3.3 ± 1.1 μM. These data strongly suggest that MhuD is a competent heme oxygenase in vivo.