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 haemoglobin or myoglobin. Type I substrate (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.
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