MECHANISMS OF STEROID OXIDATION BY MICROORGANISMS. IV. SECO INTERMEDIATES

Steroid degradation in Comamonas testosteroni

Steroid degradation by Comamonas testosteroni and Nocardia restrictus have been intensively studied for the purpose of obtaining materials for steroid drug synthesis. C. testosteroni degrades side chains and converts single/double bonds of certain steroid compounds to produce androsta-1,4-diene 3,17-dione or the derivative. Following 9α-hydroxylation leads to aromatization of the A-ring accompanied by cleavage of the B-ring, and aromatized A-ring is hydroxylated at C-4 position, cleaved at Δ4 by meta-cleavage, and divided into 2-hydroxyhexa-2,4-dienoic acid (A-ring) and 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid (B,C,D-ring) by hydrolysis. Reactions and the genes involved in the cleavage and the following degradation of the A-ring are similar to those for bacterial biphenyl degradation, and 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid degradation is suggested to be mainly β-oxidation. Genes involved in A-ring aromatization and degradation form a gene cluster, and the genes involved in β-oxidation of 9,17-dioxo-1,2,3,4,10,19-hexanorandrostan-5-oic acid also comprise a large cluster of more than 10 genes. The DNA region between these two main steroid degradation gene clusters contain 3α-hydroxysteroid dehydrogenase gene, Δ5,3-ketosteroid isomerase gene, genes for inversion of an α-oriented-hydroxyl group to a β-oriented-hydroxyl group at C-12 position of cholic acid, and genes possibly involved in the degradation of a side chain at C-17 position of cholic acid, indicating this DNA region of more than 100kb to be a steroid degradation gene hot spot of C. testosteroni. Article from a special issue on steroids and microorganisms.

Steroid 9α-Hydroxylation during Testosterone Degradation by RestingRhodococcus equiCells

The conversion pathway of testosterone to androst-4-ene-3,17-dione and 9alpha-hydroxy androstane metabolites, 9alpha-hydroxyandrost-4-ene-3,17-dione and 9alpha,17beta-dihydroxyandrost-4-en-3-one was proposed for the ring degradation in steroids by a minimal liquid medium (NMMP)-dispersed Rhodococcus equi ATCC 14887. The microorganism produced 9alpha-hydroxy androstane metabolites from testosterone at high conversion ratio without the addition of ring degradation inhibitory agents. Several NMMP-based media showed the similar effect on the microbial transformation, in which the respective molar yields of 9alpha-hydroxyandrost-4-ene-3,17-dione and 9alpha,17beta-dihydroxyandrost-4-en-3-one were approx. 3 to 47% and approx. 3 to 11%, respectively, whereas nutrient broth, a rich medium, basically showed no accumulation. On the basis of this evidence, magnesium sulfate and casamino acids among the components of NMMP were found to compromise the determinant for the production of the 9alpha-hydroxy androstane metabolites without appreciable decomposition of the steroid ring system.

Oxidative side-chain and ring fission of pregnanes by Arthrobacter simplex

Metabolic processes involving side-chain and ring cleavage of progesterone, 17-hydroxyprogesterone, 11-deoxycortisol and 16-dehydropregnenolone by Arthrobacter simplex were studied. The formation of the metabolites from progesterone indicates a pathway somewhat different from normal in the enzymic reaction sequence, and the 17-hydroxyprogesterone metabolites reveal a non-enzymic rearrangement step. The presence of a hydroxy group at C-21, as in 11-deoxycortisol, induces reduction of the C-20 carbonyl group. The microbial preparation of a novel androstane analogue, 17 beta-hydroxy-16 alpha-methoxyandrosta-1,4-dien-3-one, by incubation of 16-dehydropregnenolone with the bacterial strain was achieved. The formation of this metabolite is a multistep process involving a novel microbial generation of a methoxy group from a double-bond transformation in a steroid skeleton.

Novel transformations of i-cholesterol and 6 beta-methoxy-i-cholesterol by Moraxella sp

A soil microorganism was isolated by the enrichment culture technique using cholesterol as the sole source of carbon. The organism has been identified as belonging to the genus Moraxella. With this organism two novel biotransformations of sterols were observed viz. (1) isomerization of 3 alpha,5 alpha-cyclocholestan-6 beta-ol (i-cholesterol) to cholesterol, (2) demethylation of 6 beta-methoxy-3 alpha,5 alpha-cyclocholestane (6 beta-methoxy-i-cholesterol) to i-cholesterol with subsequent isomerization to cholesterol. The enzymes responsible for these transformations were shown to be inducible. The pH optimum of the partially purified i-cholesterol isomerase was found to be 8.4. The apparent Km value for i-cholesterol was 1.43 microM. A plausible mechanism for the i-cholesterol isomerization has been discussed.

Bioconversion of sitosterol to useful steroidal intermediates by mutants of Mycobacterium fortuitum

A series of mutants which are blocked at various stages of the sterol degradative pathway have been isolated from the potent sterol degrader Mycobacterium fortuitum ATCC-6842. Sitosterol bioconversions by these mutants result in the accumulation of a number of intermediate compounds, some of which are potentially useful as substrates in the manufacture of medically important steroids. These intermediates include androst-4-ene-3,17-dione, androsta-1,4-diene,3,17-dione, ring A-degraded tricyclic compounds and various 9alpha-hydroxy-steroids.

Microbiological degradation of bile acids. Metabolites formed from 3-(3a alpha-hexahydro-7a beta-methyl-1,5-dioxoindan-4 alpha-yl) propionic acid by Streptomyces rubescens

1. The metabolism of 3-(3a alpha-hexahydro-7a beta-methyl-1,5-dioxoindan-4 alpha-yl)propionic acid (III), which is a possible precursor of 2,3,4,6,6a beta, 7,8,9,9a alpha,9b beta-decahydro-6a beta-methyl-1H-cyclopenta[f]quinoline-3,7-dione (II) formed from cholic acid (I) by streptomyces rubescens, was investigated by using the same organism. 2. This organism effected amide bond formation, reduction of the carbonyl groups, trans alpha beta-desaturation and R-oriented beta-hydroxylation of the propionic acid side chain and skeleton cleavage, and the following metabolites were isolated as these forms or their derivatives: compound (II), 1,2,3,4 a beta,-5,6,6a beta,7,8,9a alpha,9b beta-dodecahydro-6a beta -methylcyclopental[f][1]benzopyran-3,7-dione (IVa), (1R)-1,2,3,4a beta,5,6,6a beta,7,8,9.9a alpha,9b beta-dodecahydro-1-hydroxy-6a beta-methylcyclopenta[f][1]benzopyran-3,7-dione (IVb), (E)-3-(3aalpha-hexahydro-5 alpha-hydroxy-7a beta-methyl-l-oxo-indan-4 alpha-yl)prop-2-enoic acid (V), (+)-(5R)-5-methyl-4-oxo-octane-1,8-dioic acid (VI), 3-(4-hydroxy-5-methyl-2-oxo-2H-pyran-6-yl)propionic acid (VII) and 3-(3a alpha-hexahydro-1 beta-hydroxy-7a beta-methyl-5-oxoindan-4 alpha-yl)propionic acid (VIII). The metabolites (IVb), (V), (VI) and (VII) were new compounds, and their structures were established by chemical synthesis. 3. The question of whether these metabolites are true degradative intermediates is discussed, and a degradative pathway of compound (III) to the possible precursor of compound (VII), 7-carboxy-4-methyl-3,5-dioxoheptanoyl-CoA (IX), is tentatively proposed. The further degradation of compound (IX) to small fragments is also considered.

The bacterial transformation of abietic acid

An Alcaligenes species, which was isolated from soil, can utilize abietic acid as its sole carbon source. During growth, the bacterium transforms abietic acid into 5alpha-hydroxyabietic acid (I, R=OH), a product considered to be 7beta-hydroxy-13-isopropyl-8xi-podocarp-13-en-15-oic acid (II, R=H) and a compound, C(20)H(28)O(3), which is believed to be an epoxy-gamma-lactone.