title: Rat liver cytochrome P-450b, P-420b, and P-420c are degraded to biliverdin by heme oxygenase.
abstract: In this report we provide data, for the first time, demonstrating the conversion of the heme moiety of certain cytochrome P-450 and P-420 preparations, to biliverdin, catalyzed by heme oxygenase. We have used purified preparations of cytochromes P-450c, P-450b, P-450/P-420c, or P-450/P-420b as substrates in a heme oxygenase assay system reconstituted with heme oxygenase isoforms, HO-2 or HO-1, NADPH-cytochrome c (P-450) reductase, biliverdin reductase, NADPH, and Emulgen 911. With cytochrome P-450b or P-450/P-420b preparations, a near quantitative conversion of degraded heme to bile pigments was observed. In the case of cytochrome P-450/P-420c approximately 70% of the degraded heme was accounted for as bilirubin but only cytochrome P-420c was appreciably degraded. The role of heme oxygenase in this reaction was supported by the following observations: (i) bilirubin formation was not observed when heme oxygenase was omitted from the assay system; (ii) the rate of degradation of the heme moiety was at least threefold greater with heme oxygenase and NADPH-cytochrome c (P-450) reductase than that observed with reductase alone; and (iii) the presence of Zn- or Sn-protoporphyrins (2 microM), known competitive inhibitors of heme oxygenase, resulted in 70-90% inhibition of bilirubin formation.
mesh_terms: D000818:Animals; D001663:Bilirubin / Q000031:analogs & derivatives*; D001664:Biliverdine / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism*; D006418:Heme / Q000378:metabolism*; D006419:Heme Oxygenase (Decyclizing) / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008665:Metalloporphyrins; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors; D011524:Protoporphyrins / Q000494:pharmacology; D051381:Rats; D013053:Spectrophotometry
chemical_list: D003580:Cytochromes; D007527:Isoenzymes; D008665:Metalloporphyrins; D011524:Protoporphyrins; C017803:zinc protoporphyrin; D006418:Heme; C013464:cytochrome P420; D003577:Cytochrome P-450 Enzyme System; C032628:tin protoporphyrin IX; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; D006419:Heme Oxygenase (Decyclizing); D044925:Oxidoreductases Acting on CH-CH Group Donors; C019789:biliverdin reductase; D009251:NADPH-Ferrihemoprotein Reductase; D001664:Biliverdine; D001663:Bilirubin