title: Features of intermediary steps around the 688-nm substance in the heme oxygenase reaction.
abstract: The degradation of protoheme in the heme oxygenase reaction involves three oxidation steps: from protoheme to hydroxyheme, from hydroxyheme to a 688-nm substance, a protein-bound intermediate, and from the 688-nm substance to a biliverdin-iron complex. The 688-nm substance has a ferrous iron and it readily binds carbon monoxide to form a CO-complex, called the 638-nm substance (Yoshida, T., Noguchi, M., & Kikuchi, G. (1980) J. Biochem. 88, 557-563). The ferric 688-nm substance was prepared from the 638-nm substance by the addition of potassium ferricyanide together with aspiration to eliminate CO. The ferric 688-nm substance did not show any distinct absorption maximum in the red region of the absorption spectrum. The ferric 688-nm substance was readily reduced on the addition of the NADPH-cytochrome P-450 reductase system, but the ferric 688-nm substance could also be reduced spontaneously though at a very low rate. The ferrous 688-nm substance free from excess reducing agents was prepared by passing the 638-nm substance through a column of Sephadex G-25. The ferrous 688-nm substance was degraded to a biliverdin-iron complex much more rapidly in the presence of the NADPH-cytochrome P-450 reductase system than in its absence, indicating that a reducing equivalent is essential for the initiation of heme degradation even when starting from the ferrous 688-nm substance. Cyanide was found to bind to the ferrous 688-nm substance to form a stable compound; the cyanide compound formed could revert to neither the ferrous 688-nm substance nor the 638-nm substance.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001663:Bilirubin / Q000302:isolation & purification; D006418:Heme / Q000302:isolation & purification; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism*; D007501:Iron / Q000032:analysis; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010084:Oxidation-Reduction; D013053:Spectrophotometry; D013154:Spleen / Q000201:enzymology; D013552:Swine
chemical_list: D006418:Heme; D007501:Iron; D006899:Mixed Function Oxygenases; D006419:Heme Oxygenase (Decyclizing); D009251:NADPH-Ferrihemoprotein Reductase; D001663:Bilirubin