THE HYBRID RAT CYTOCHROME-P450 CONTAINING THE FIRST 5 EXONS OF THE CYP11B1 AND LAST 4 EXONS FROM THE CYP11B2 ENZYME RETAINS 11-BETA-HYDROXYLASE ACTIVITY, BUT THE ALTERNATIVE HYBRID IS INACTIVE

Human, mouse and rats have 2 different cytochrome P-450 11 beta-hydrox ylases in the adrenal cortex. The classical rat 11 beta-hydroxylase or CYP11B1 enzyme hydroxylates deoxycorticosterone to corticosterone and 18-hydroxydeoxycorticosterone and is located throughout the adrenal. The second aldosterone synthase or CYP11B2 enzyme is located in the zo na glomerulosa and converts deoxycorticosterone to corticosterone, 18- hydroxycorticosterone and aldosterone. In rat the coding nucleotide se quence and the deduced amino acid sequences of the CYP11B1 and CYP11B2 genes are homologous by 88% and 83%,respectively. We have constructed two different hybrid cDNAs by exchanging two fragments of the rat CYP 11B1 and CYP11B2 at the junction of the 5/6 exon and expressed them in COS7 cells. The hybrid CYPH11B1 construct containing the first 5 exon s of the CYP11B1 when expressed, retains 11 beta-hydroxylase activity, but cannot process corticosterone to 18-hydroxycorticosterone or aldo sterone. The hybrid CYPH11B2 construct containing the first 5 exons of the CYP11B2 enzyme when expressed is inactive. (C) 1994 Academic Pres s, Inc.