Steroids, hydroxylation metabolism

A screening of about 40 strains currently used for steroid hydroxylation was undertaken, using reverse-phase HPLC and UV absorption to detect and quantitate metabolite formation. Most of the strains tested were able to metabolize extensively this substrate within a 1- to 5-day period, producing in the incubation medium variable amounts of at least eight hydroxylated metabolites (80-87), essentially depending on the strain used [189]. 

Iron-sulfur proteins contain non-heme iron and inorganic (acid-labile) sulfur in their active centers as 4Fe-4S or 2Fe-2S or, in the case of rubredoxin, as one iron alone. The iron is always bonded to cysteine sulfur. They catalyze redox reactions between +350 and —600 mV (hydrogen electrode = —420 mV). They are usually of low molecular weight (6000-15,000 Daltons) but can form complex enzymes with molybdenum and flavin. They occur as soluble or membrane-bound proteins and catalyze key reactions in photosynthesis, oxidative phosphorylation, nitrogen fixation, H2 metabolism, steroid hydroxylation, carbon and sulfur metabolism, etc. They occur in all organisms so far investigated and may... 

Steroid-metabolizing mitochondria, e.g., those from beef adrenal cortex (76, 82-84) and porcine corpus luteum (86, 86), were recently shown to contain an active energy-linked transhydrogenase that appears to play a role in steroid hydroxylation reactions (see Section IV). Under proper assay conditions all mitochondrial transhydrogenases hitherto described may be coupled to respiratory energy or ATP. 

Copper complex modulation of steroid hydroxylations have also been reported [690]. A single dose of Cu(II)sulphate injected into rats caused a 2-to 3-fold increase in adrenal copper, a significant (P < 0.05) increase in mitochondrial P-450-dependent steroid 11-jS-hydroxylase activity, and an 85% increase in concentration of P-450 as well as a 3-fold increase in fi-aminolevuli-nate synthetase, which suggests a positive feedback stimulation of P-450 synthesis. Chronic treatment with Cu(II)sulphate for 7 days caused a decrease in 11-jS-hydroxylase activity (P<0.05) and a decrease in plasma corticosterone concentration (P<0.05) while there was a concomitant increase in cholesterol side-chain cleavage, suggesting the metabolism of cholesterol by some other P-450 following maximal corticosterone synthesis. A positive feedback for 6-aminolevulinate synthesis was also evidenced by an increase in synthetase activity. 

Oxidoreductases have a variety of functions in metabolism oxidases and dehydrogenases play major roles in respiration hydroperoxidases protect the body against damage by free radicals and oxygenases mediate the hydroxylation of drugs and steroids. 

Microbial transformations of four heteroyohimbine stereoisomers [ajmalicine (81a) tetrahydroalstonine (81b), isoajmalicine (81c), and akumigine (81d)] yielded mixtures of 10- and 11-hydroxylation products (786) (Scheme 21). Microorganisms known for their abilities to metabolize indole alkaloids, steroids, and antibiotics were intitially screened, and seven cultures were further used for preparative-scale incubations with alkaloid substrate. The microorganisms used and yields (by HPLC) of metabolites obtained from 81a-81d are shown in Table HI. 

This agrees very much with the model proposed by Peterson et al. (8) for the 5-exo hydroxylation of d and 1 camphor in mammalian cytochrome P-450/ and is also consistent with the relationship they noted from steroid metabolism by cytochrome P-450/ between the position hydroxylated and its relation to a polar funtional group. 

The steroid hormones are mainly inactivated in the liver, where they are either reduced or further hydroxylated and then conjugated with glucuronic acid or sulfate for excretion (see p. 316). The reduction reactions attack 0X0 groups and the double bond in ring A. A combination of several inactivation reactions gives rise to many different steroid metabolites that have lost most of their hormonal activity. Finally, they are excreted with the urine and also partly via the bile. Evidence of steroids and steroid metabolites in the urine is used to investigate the hormone metabolism. 

Approximately 50% of a dose of mestranol is de-methylated to form ethinyl estradiol. Ethinyl estradiol also can be deethinylated. Subsequently, the metabolism of these two synthetic estrogens proceeds by means of the same pathways as the natural steroid hormones. The principal metabolites of mestranol and ethinyl estradiol are hydroxylated derivatives that are conjugated with either glucuronic acid or sulfate. The synthetic steroid estrogens, in contrast to the natural estrogens, are excreted primarily in the feces. 

Microbial and enzymic transformations of steroids have been reviewed. 5a-Pregnane-7,20-dione gave a reasonable yield of the la, 12/3-dihydroxy-derivative on incubation with Calonectria decora High yields of 10 8-hydroxy-19-nortes-tosterone were obtained by incubation of 19-nortestosterone with Rhizopus arr-hizus (Fischer 11). Oxidation of canrenone with a Penicillium species provided the 15a-hydroxy-derivative (348) which is a product of human metabolism of spironolactone.16j8-Hydroxylation of androstenolone, androst-4-ene-3,17-... 

Cardenolldes appear to be metabolized by a variety of species, possibly as a mechanism for converting these steroids into compounds that can be efficiently sequestered. The milkweed bug, Oncopeltus fasclatus, metabolizes (hydroxylates ) the nonpolar cardenollde dlgltoxln to more polar compounds that are subsequently sequestered In the dorsolateral space fluid (17. 18). Larvae of another cardenolide-adapted Insect, the monarch butterfly, Danaus plexlppus. also convert these steroids Into compounds that are readily sequestered. For example, uscharldln, which contains a carbonyl group at C-3 ( ) of the... 

Cytochromes P450 form a very large group of heme enzymes that catalyze the hydroxylation of a variety of substrates. They are important in drug metabolism, in cholesterol and steroid hormone biosynthesis, and in numerous other pathways. They have been found to participate in reactions other than hydroxyla-tions. 

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