Detection of aromatase cytochrome P450, 17 alpha-hydroxylase cytochrome P450 and NADPH:P450 reductase on the surface of cells in which they are expressed

Using the membrane impermeant probe NHS-LC-biotin, we show in this report that a fraction of aromatase P450 (P450arom), the enzyme that catalyzes estrogen biosynthesis, is present Lit the surface of cells in which it is expressed, either endogenously or as a consequence of transfection. The same findings were obtained for a truncated form of P450arom lacking the putative membrane-spanning region: thus suggesting the presence of other melmbrane-spanning region(s) within its structure. P450arom is not unique in this regard as we find that a fraction of 17 alpha-hydroxylase P450 as well as NADPH:P450 reductase also are present at the cell surface. It is therefore possible that a number of microsomal P450s are expressed al the cell surface in this fashion,