title: Reaction of the microsomal heme oxygenase with cobaltic protoporphyrin IX, and extremely poor substrate.
abstract: A reconstituted heme oxygenase system which was  composed of a purified heme oxygenase from pig spleen microsomes and a partially purified NADPH-cytochrome c reductase from pig liver microsomes could not catalyze the conversion of cobaltic protoporphyrin IX (Co-heme) to biliverdin, although Co-heme could bind with the heme oxygenase protein to form a complex. The heme oxygenase system in the microsomes from pig spleen, rat spleen, and rat kidney also failed to oxidize Co-heme to biliverdin. Properties of the complex of Co-heme and heme oxygenase closely resembled those of cobalt myoglobin and cobalt hemoglobin; the Co-heme bound to the heme oxygenase protein did not react with cyanide and azide, the Co-heme moiety was reduced but only slowly with sodium dithionite, and the reduced form of the Co-heme did not appear to bind carbon monoxide. The co-heme bound to heme oxygenase was not reduced with the NADPH-cytochrome c reductase system in air. These findings further support the views that heme oxygenase may have a heme-binding crevice similar to those of myoglobin and hemoglobin and that reduction of heme is the prerequisite for the oxidative degradation of heme in the heme oxygenase reaction.
mesh_terms: D000818:Animals; D003035:Cobalt; D005260:Female; D006418:Heme; D007668:Kidney / Q000201:enzymology; D008861:Microsomes / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D011166:Porphyrins; D011485:Protein Binding; D011524:Protoporphyrins; D051381:Rats; D013053:Spectrophotometry; D013154:Spleen / Q000201:enzymology; D013552:Swine
chemical_list: D011166:Porphyrins; D011524:Protoporphyrins; D003035:Cobalt; D006418:Heme; D006899:Mixed Function Oxygenases; D009251:NADPH-Ferrihemoprotein Reductase