Hydroxylation of steroids by microorganisms

Three groups of 3-keto-4-ene steroids with different side chains were used as substrates for the induced 11 alpha-hydroxylase of Rhizopus nigricans. The highest total bioconversion as well as the highest yield of 11 alpha-hydroxylated product is found using progesterone as substrate. By changing the polarity of the side chain, much higher yields of 6 beta- and 7 beta-hydroxylated products relative to 11 alpha-hydroxylated product are obtained. Our results thus provide evidence for the importance of the side chain in steroid-enzyme interactions.

Three major classes of steroids include sterols, steroid hormones, and bile acids. Perhaps the most important sterol, cholesterol, serves as the precursor of both steroid hormones and bile acids. The synthesis of these compounds requires hydroxylation reactions. In addition, steroid-like substances such as vitamin D also undergo hydroxylation reactions. Many of these reactions are performed by the cytochrome P450 superfamily of enzymes. The many different forms of cytochrome P450 oxidize a wide variety of substrates. Moreover, in recent years, it has become apparent that many of these reactions exhibit remarkable regio- or stereoselectivity. For the most part, hydroxylation serves to increase the polarity of the rather hydrophobic steroids. By increasing their aqueous solubility, the hydroxyl functionalities may make certain substances bioactive. Conversely, oxidation may also facilitate the urinary excretion of the compounds. Many microorganisms are capable of steroid hydroxylation. In addition, competitive, noncompetitive, and mechanism-based inhibitors exist for these reactions. Steroid substances are also used to achieve a number of therapeutic objectives. The pharmacologic potential of these compounds may be altered through hydroxylation. Steroids such as cholesterol, the steroid hormones, and the bile acids, serve a diverse range of functions (5:59). These compounds are, for the most part, water insoluble. Hence, it is primarily through different hydroxylation reactions that the compounds achieve their various physiologic effects. The sterol, cholesterol, serves as the major steroid precursor. This compound--which is derived from acetyl coenzyme A--represents an integral component of eukaryotic membranes (14:474-482). It gives rise to five different types of steroid hormones. These include the following categories: (1) the progestagens; (2) the glucocorticoids; (3) the mineralocorticoids; (4) the ...

Hydroxylation of steroids by microorganisms

hydroxylation of steroids by microorganisms

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