In the past decade there has been considerable progress in the characterization of individual human P450 enzymes. These advances were initiated by early work on the purification of individual enzymes from human liver and other sources. The early work in the area was guided by a focus on the most abundant and easily purified enzymes.1–4It is now apparent, in retrospect, that these proteins were in the 2C and 3A families. Efforts were shifted to attempts to purify individual P450s on the basis of catalytic activities with the evidence that in some cases a single P450 could be identified in this way; e.g., the P450 now known as P450 2D6 was found to be under monogenic control. 5 The approach is technically demanding because of the need to do separations in the presence of detergents and then remove them before analysis of catalytic activity. Nevertheless, human P450s 1A1,6 1A2,7 2A6,8 2C8,9 2C9,9,10 2D67,11,12 2E1 13,14 3A4,15 3A5,16 4A11,17 and lanosterol 14α-demethylase18 were isolated in this general manner. Another approach that has been used, sometimes in a mode complementary to catalytic specificity, is purification on the basis of immunochemical similarity to animal P450s. 7,11,19,20

Human Cytochrome P450 Enzymes

Regulation of Aldosterone Biosynthesis

Zonal distribution of aldosterone synthase cytochrome P-450 and cytochrome P-45011 beta in rat adrenocortex was investigated immunochemically using specific antibodies to these enzymes. Localization of aldosterone synthase cytochrome P-450 (cytochrome P-450aldo), a recently identified enzyme that converts deoxycorticosterone to aldosterone in rat adrenocortex was strictly confined to two or three outermost cell layers in the zona glomerulosa. In contrast, cytochrome P-45011 beta, which forms corticosterone, but not aldosterone, from deoxycorticosterone, was localized in the zona fasciculata-reticularis and not in the zona glomerulosa. Neither enzyme was detected in the medulla or the capsule. The functional zonation of adrenocortex with respect to aldosterone and corticosterone syntheses is, thus, ascribable to the localization of cytochromes P-450aldo and P-45011 beta in the respective zones. When rats were maintained under Na-depleted conditions for 10 days, the zona glomerulosa cells containing cytochr...

Zone-specific expression of aldosterone synthase cytochrome P-450 and cytochrome P-45011 beta in rat adrenal cortex: histochemical basis for the functional zonation.

Cloning and expression of a cDNA for human cytochrome P-450aldo as related to primary aldosteronism.

Isolation of aldosterone synthase cytochrome P-450 from zona glomerulosa mitochondria of rat adrenal cortex.

Aldosterone biosynthesis and cytochrome P-45011 beta: evidence for two different forms of the enzyme in rats.

Monoclonal antibodies against bovine adrenal cytochrome P-45011β and cytochrome P-450scc. Their isolation, characterization and application to immunohistochemical analysis of adrenal cortex

The testis and ovary of normal and 3-methylcholanthrene-treated mice were studied ultrastructurally and immunohistochemically in order to learn whether steroid-secreting cells of the gonads are involved in drug metabolism. The steroid-secreting cells, i.e., Leydig cells of the testis, and theca interna cells, interstitial gland cells, and corpus luteum cells of the ovary of 3-methylcholanthrene-treated mice, show a strong positive reaction to the antiserum against, hepatic microsomal cytochrome P-450, of liver which is the terminal oxidase of the drug-metabolizing enzyme complex. In addition, it was found that elements of smooth endoplasmic reticulum (SER) in drug-treated mice become well developed as compared with those in control animals. These findings indicate that the steroid secreting cells in testis as well as ovary are involved in the metabolism of both endogenous and exogenous chemical compounds.

Ultrastructural and immunohistochemical studies on steroid-secreting cells of the testis and ovary of normal and 3-methylcholanthrene-treated mice

The drug-metabolism activity of adrenocortical cells of normal and 3-methylcholanthrene (MC)-treated ddY mice were examined ultrastructurally and immunohistochemically. Immunoblot analyses performed prior to immunohistochemistry revealed the presence of a protein — possible equivalent to cytochrome P-450 found in the liver microsomes of MC-treated male rats — in the adrenal homogenate of MC-treated female mice. Immunohistochemistry demonstrated the presence of a cytochrome-P-450-like protein in the adrenal-cortical cells (especially in the zona-reticularis cells) of MC-treated female mice; at the same time, a remarkable increase in the amount of SER in these cells was observed by electron microscopy. These findings suggest that cells of the mouse adrenal gland, particularly those of the zona-reticularis, might participate not only in steroid biosynthesis but also in some sort of drug metabolism (detoxication). In addition, there might be a sex-related difference in ddY mice.

S. Sugano

Papers

Aldosterone biosynthesis and cytochrome P-45011 beta: evidence for two different forms of the enzyme in rats.

Monoclonal antibodies against bovine adrenal cytochrome P-45011β and cytochrome P-450scc. Their isolation, characterization and application to immunohistochemical analysis of adrenal cortex

Ultrastructural and immunohistochemical studies on steroid-secreting cells of the testis and ovary of normal and 3-methylcholanthrene-treated mice

Ultrastructural and immunohistochemical studies on the zona-reticularis cells of the adrenal cortex of normal and 3-methylcholanthrene-treated mice.