Constitutive and inducible expression of human cytochrome P450IA1 in yeast Saccharomyces cerevisiae: An alternative enzyme source for in vitro studies

Abstract

A cDNA of human cytochrome P450IA1 was expressed in yeast Saccharomyces cerevisiae on a multicopy plasmid under the control of the constitutive GAPFL or the inducible PHO5 promoter. Microsomes of transformed yeast contained substantial amounts of the heterologous enzyme as determined by reduced CO-difference spectra (156-68 pmol/mg). Enzyme kinetics with 7-ethoxyresorufin as substrate resulted in a K m value of 92 nM and a V max value of 223 pmol/mg/min, which is comparable to data obtained with human liver microsomes. The antimycotic drug ketoconazole (K i=22nM) as well as the isozyme specific P450 inhibitor α-naphthoflavone (K i=1.2nM) were shown to be strong inhibitors of human P450IA1. Taken together, these data show that heterologous P450 gene expression in yeast is a potent instrument for the study of enzyme specific parameters and might be used to answer further questions with regard to substrate specificity as well as drug interaction in a background with no interfering activities.