MODULATION OF HYDROXYLASE AND LYASE ACTIVITIES OF BOVINE CYTOCHROME P-450(17-ALPHA) IN ADRENAL AND TESTICULAR MICROSOMES BY A TISSUE-SPECIFIC LOCAL MEMBRANE ENVIRONMENT

In steroidogenic tissues, cytochrome P-450(17 alpha), catalyzes both steroid 17 alpha-hydroxylation and 17,20-lyase reactions. The ratio of the two activities, hydroxylase over lyase (H/L) depends upon the tissue of origin; this ratio is low in the testis whereas it is high in the adrenal cortex. To examine the factors responsible for this specific regulation, two approaches were followed: (i) the purified enzyme was incorporated into liposomes made of microsomal lipids of testis or adrenal cortex; and (ii) the effects of disorganization of the microsomal membrane on the activities were observed. The results show that the cytochrome 17,20-lyase activity is stimulated by the presence of lipids from testicular origin. In the adrenal microsomes, this activity appears to be dependent upon the local membrane organization. Specific component(s) associated with the neutral fraction of the microsome lipid extract may be responsible for the repression of lyase activity in the adrenal.