EXPRESSION AND CHARACTERIZATION OF A HEME OXYGENASE (HMU-O) FROM CORYNEBACTERIUM-DIPHTHERIAE - IRON ACQUISITION REQUIRES OXIDATIVE CLEAVAGEOF THE HEME MACROCYCLE

A full-length heme oxygenase gene from the pathogenic bacterium Coryne bacterium diphtheriae has been subcloned and expressed in Escherichia coil. The enzyme is expressed at high levels as a soluble catalyticall y active protein that results in the accumulation of biliverdin within the E. coil cells. The purified heme oxygenase forms a 1:1 complex wi th heme (K-d, 2.5 +/- 1 mu M) and has hemeprotein spectra similar to t hose previously reported for the purified eukaryotic heme oxygenases. In the presence of an E. coil NADPH-dependent reductase isolated durin g the purification of Hmu O, the heme-Hmu O complex is catalytically t urned over to yield biliverdin IX alpha and carbon monoxide, A number of redox partners were investigated for their ability to reconstitute Hmu O activity in vitro. Of these the most efficient appeared to be th e recombinant NADH-dependent putidaredoxin/putidaredoxin reductase fro m Pseudomonas putida. As with the E. coli NADPH-dependent reductase th e final products of the reaction were biliverdin IX alpha and carbon m onoxide. This is the first bacterial heme oxygenase to be described to date. The close relationship between iron acquisition and pathogenesi s suggests that the release of iron from heme by heme oxygenase may pl ay a crucial role in the pathogenicity of C. diphtheriae.