Arylhydrocarbon hydroxylase activity and cytochrome P-450 in human tissues

The stability and distribution of arylhydrocarbon hydroxylase activity in four human tissues has been examined. Two tissues, liver and lung, were obtained from autopsy samples while lymphocytes and placenta were obtained from cell lines and donors. Marked differences in arylhydrocarbon hydroxylase activity were observed between tissues and individuals, with liver being the richest source. Activity in all tissues was stable at 4 degrees C for 24 h, but freeze-thawing markedly reduced hydroxylase activity in liver. Using gel exclusion chromatography, the molecular weight of a non-dissociated form of arylhydrocarbon hydroxylase was estimated to be about 400000. A heme staining band corresponding to a molecular weight of 50000 was observed after polyacrylamide gel electrophoresis of liver microsomal preparations. This appears to be a cytochrome P-450 subunit based on correlations between staining intensity and hydroxylase activity in tissues and partially purified preparations examined.