Haem accessibility in cytochrome P-450 from rabbit liver. A proton magnetic relaxation study by stereochemical probes.
Cytochrome P-450 was solubilized from phenobarbital induced rabbit liver and purified by affinity chromatography. The longitudinal proton magnetic relaxation rates of this ferric, low-spin sample (as confirmed by ESR) in 20% glycerol aqueous solution are very large compared with low-spin methaemoglobin and myoglobin derivatives. Similarly high rates were measured in a deuterated solution using the aliphatic protons of glycerol as stereochemical markers, which strongly suggests that the haem iron in cytochrome P-450 is much more accessible to the solvent than in harmoglobin or myoglobin. Type I substate (Spasman) produced small but significant increases in NMR rates both in the H2O and in the 2H2O solution, while binding of aniline (Type II substrate) doubled the rates.
D001665:Binding Sites; D002846:Chromatography, Affinity; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000302:isolation & purification; D004578:Electron Spin Resonance Spectroscopy; D004790:Enzyme Induction; D006418:Heme / Q000032:analysis; D007501:Iron / Q000032:analysis; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D010634:Phenobarbital / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D013696:Temperature
D006418:Heme; D003577:Cytochrome P-450 Enzyme System; D007501:Iron; D010634:Phenobarbital