title: Studies on heme d1 extracted from Pseudomonas aeruginosa nitrite reductase.
abstract: Heme d1 has been extracted from Pseudomonas nitrite reductase. Imidazole, cyanide, and chloride-ferroheme, and CO, NO, cyanide, imidazole, and pyridine-ferroheme complexes have been prepared for study by UV/vis spectroscopy, and in some cass by epr and low-temperature mcd as well. Iron determinations have been carried out to assess extinction coefficients. Absorption spectra were used to monitor the transition of chloride-ferriheme d1 to an alkaline form of ferriheme d1 and a pka of 6.5 was determined for the process. The epr spectrum of chloride-ferriheme possessed the characteristic g = 6 signal of high spin (S = 5/2) iron, but the alkaline-ferriheme form gave no detectable epr signals. Electron paramagnetic resonance spectra were also obtained for cyanide and imidazole-ferriheme d1 and for NO-ferroheme d1. The imidazole complex gave signals that were very weak in comparison with the cyanide complex, but mcd measurements of imidazole-ferriheme d1 were consistent with it being a low-spin (S = 1/2) system. The epr signals of NO-ferroheme d1 were similar to those of the corresponding holo-enzyme complex. Reduction of alkaline-ferriheme d1 was found to be affected by the presence of oxygen, but under N2 give the same result with ascorbate and dithionite. Autoreduction of alkaline-ferriheme d1 was observed when placed under CO, and NO, atmospheres, or when treated with pyridine.
mesh_terms: D002248:Carbon Monoxide; D003486:Cyanides; D004227:Dithionite; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000031:analogs & derivatives* / Q000302:isolation & purification; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles; D007501:Iron; D009247:NADH, NADPH Oxidoreductases; D009569:Nitric Oxide; D009572:Nitrite Reductases; D011485:Protein Binding; D011550:Pseudomonas aeruginosa / Q000201:enzymology*; D013053:Spectrophotometry
chemical_list: D003486:Cyanides; D007093:Imidazoles; D004227:Dithionite; D009569:Nitric Oxide; D006418:Heme; C029400:heme d1; D002248:Carbon Monoxide; D007501:Iron; D009247:NADH, NADPH Oxidoreductases; D009572:Nitrite Reductases