[Basic characteristics of rat brain microsomal estradiol 2-hydroxylase].

The basic properties of estradiol 2-hydroxylase in rat brain microsomes were studied and compared to the known characteristics of rat liver microsomal estradiol 2-hydroxylase. Rat liver microsomal estradiol 2-hydroxylase, which has been considered to be a cytochrome P450-like enzyme, was largely inhibited by carbon monoxide. On the other hand, the effect of carbon monoxide on the activity of rat brain microsomal estradiol 2-hydroxylase was rather weak. A known inhibitor of cytochrome P450, SKF-525A inhibited rat liver microsomal estradiol 2-hydroxylase in a concentration-dependent manner. The concentration of SKF-525A causing 50% inhibition of liver microsomal estradiol 2-hydroxylase was 33 microM where the substrate concentration was 1 microM. Conversely, the inhibitory effect of SKF-525A on the activity of brain microsomal estradiol 2-hydroxylase was much less. Moreover, norepinephrine inhibited brain microsomal estradiol 2-hydroxylase in a competitive manner, however, the effect of physiological concentrations of norepinephrine on liver microsomal estradiol 2-hydroxylase was negligible. These results suggest that the nature of microsomal estradiol 2-hydroxylase in rat brain is quite different from that of liver microsomal estradiol 2-hydroxylase.