Microsomal 11a-hydroxylation of progesterone in Image : Part I: Characterization of the hydroxylase system

Microsomes (105,000xg sediment) prepared from induced cells of Image was found to hydroxylate progesterone to 11a-hydroxyprogesterone (11a-OHP) in high yields (85-90% in 30 min.) in the presence of NADPH and O2. The pH optimum for the hydroxylase was found to be 7.7. However, for the isolation of active microsomes grinding of the mycelium should be carried out at pH 8.3. Metyrapone, carbon monoxide, SKF-525A, p-CMB and N-methyl maleimide inhibited the hydroxylase activity indicating the involvement of cytochrome P-450 system. The inhibition of the hydroxylase by cytochrome Image and the presence of high levels of NADPH-cytochrome Image reductase in induced microsomes suggest that the reductase could be one of the components in the hydroxylase system.