11 alpha-Hydroxylation of progesterone by cell free preparation of Aspergillus ochraceus TS

Yeast as a promising heterologous host for steroid bioproduction

With the rapid development of synthetic biology and metabolic engineering technologies, yeast has been generally considered as promising hosts for the bioproduction of secondary metabolites. Sterols are essential components of cell membrane, and are the precursors for the biosynthesis of steroid hormones, signaling molecules, and defense molecules in the higher eukaryotes, which are of pharmaceutical and agricultural significance. In this mini-review, we summarize the recent engineering efforts of using yeast to synthesize various steroids, and discuss the structural diversity that the current steroid-producing yeast can achieve, the challenge and the potential of using yeast as the bioproduction platform of various steroids from higher eukaryotes.

Study of mixed function oxidase system in Aspergillus ochraceus (NCIM 1146)

Aspergillus ochraceus (NCIM-1146) has shown the ability to degrade cholesterol, camphor and naphthalene, when 96 h grown mycelium incubated in medium containing these organic compounds. Presence of higher level of electron transport components and biotransformation enzyme activity were observed in Aspergillus ochraceus, when grown in potato dextrose medium for 96 h. The enzyme activity preferred NADPH as a cofactor and shows inhibition in the presence of CO, indicating cytochrome P-450 mediated reactions. A significant increase in the levels of electron transport components and biotransformation enzyme activity were observed in presence of different inducers (viz. cholesterol, camphor, naphthalene, veratrole, phenobarbital, n-hexane, kerosene and saffola oil) when compared with mycelium incubated in same way with similar conditions for 2 min incubation. Analyses of the products of cholesterol and camphor using HPLC and GCMS confirm the degradation of these compounds.

Molecular analysis of variability within the toxigenic Aspergillus ochraceus species

Genetic variability of Aspergillus ochraceus was examined at the DNA level. Based on the HaeIII-Bg/II generated mitochondrial DNA restriction profiles, most isolates could be classified into two distinct groups. These two groups could also be distinguished by the random amplified polymorphic DNA technique, and with telomeric PCR amplifications. Phylogenetic analysis of sequences of the intergenic transcribed spacer region of some of the strains resulted in a dendrogram with the same topology as that based on mitochondrial DNA and amplified DNA data. None of the isolates with type 2 mtDNA profiles produce ochratoxins. Some strains (e.g., A. ochraceus ICMP 939) displayed strain-specific mitochondrial DNA patterns, and their amplified DNA profiles were also different from all other A. ochraceus strains examined.

Evidence for and characterization of cytochrome P-450 in Neurospora crassa

Cytochrome P-450 was detected in microsomes and presumably in cytosol of Neurospora crassa, and was found to be inducible by progesterone. In the microsomal fraction cytochrome b5 and NADPH-cytochrome c reductase activities were measurable, too. Cytochrome P-450 of Neurospora crassa is inhibited by SKF-525 A and by inhibitors of ergosterol biosynthesis. After induction of cytochrome P-450 with progesterone 11 alpha-hydroxyprogesterone as one metabolite of progesterone was detected in the culture media as well as in the mycelia. After 42 hours about 70% of progesterone were metabolized.

Microbial transformation of steroids--VII. Hydroxylation of progesterone by extracts of Phycomyces blakesleeanus

Post mitochondrial supernatants (S-12 extracts) were prepared from Phycomyces blakesleeanus by grinding washed and frozen mycelial cakes in fine sand and extracting the paste produced with buffer containing Tris-HCl pH 7.8 (0.1 M), EDTA (0.01 M), dithiothreitol (5 mM) and glycerol (10% v/v). The S-12 extracts, obtained in this way, reproducibly hydroxylated progesterone, producing 7 alpha- and 15 beta-hydroxyprogesterone the major products of whole-cell transformation. Cell-free progesterone hydroxylation was found to be approximately linearly dependent on extract concentration, to require reduced NADP (partly replaceable by NADH), and to be dependent on progesterone (apparent Km calculated to be 4 mM). K+ and Mg2+ were found not to be required. Maximum progesterone hydroxylation occurred after 2 h at pH 7.8 and at 24 degrees C. Using optimum conditions S-12 extracts were capable of hydroxylating between 5 and 15% of added progesterone (0.2 mM). Hydroxylation was found to be partially inhibited by carbon monoxide (ca 40%) and almost completely inhibited by azoles, ketoconazole and diconazole. The NADPH and molecular oxygen requirements were replaceable by NaIO4. These findings strongly suggest that hydroxylation was being catalyzed by cytochrome P-450. This was confirmed by preparing progesterone-hydroxylating microsomes and Triton N-101-solubilized microsome extracts, and by obtaining a dithionite-reduced carbon monoxide-difference absorption spectrum peak at 455 nm in the solubilized microsome extracts.

Correlation of biocatalytic activity in an organic-aqueous two-liquid phase system with solvent concentration in the cell membrane

Results presented here show that loss of progesterone 11 alpha-hydroxylase activity in Rhizopus nigricans in aqueous-organic two-liquid phase and cosolvent systems correlates well with the concentration of solvent in the cell membranes. Rhizopus nigricans is shown to retain full 11 alpha-hydroxylase activity at saturating aqueous phase concentrations of hexane and the higher primary alcohols. This reflects their inability to attain a critical concentration in the cell membranes. The relationship between our own findings and the previously described correlation of the logarithm of the partition coefficient with activity retention is explained and design parameters are proposed that may be used to select solvents for future biocatalytic systems.

Microbial transformation of steroids--II. Transformations of progesterone, testosterone and androstenedione by Phycomyces blakesleeanus

Phycomyces blakesleeanus transformed progesterone, testosterone and androstenedione into mixtures of products. Five monohydroxylated metabolites were obtained in reasonable yields from the progesterone transformation. Only 7 alpha- and 15 beta-hydroxyprogesterone have been reported previously from this organism. We find that it gives these two metabolites and also 6 beta-, 14 alpha- and 15 alpha-hydroxyprogesterone as major products. Five compounds were also purified from testosterone transformation mixtures. Two of these were monohydroxylated, two were ring A dehydrogenation products, and two were oxidised at C-17. The products were identified as 6 beta-hydroxytestosterone, 7 alpha-hydroxytestosterone, androsta-1,4-diene-3,17-dione (1-dehydroandrostenedione), 17 beta-hydroxyandrosta-1,4-diene-3-one (1-dehydrotestosterone) and androstenedione. All five metabolites were produced in reasonable yields, although hydroxylation was the minor transformation in this case. Only two significant products were formed from androstenedione. Both were reduced at C-17; one was also monohydroxylated. They were testosterone and 14 alpha-hydroxytestosterone. The testosterone and androstenedione transformation products have not been reported previously for this organism. We also report for the first time the preparation of P. blakesleeanus cell-free extracts which transformed progesterone reasonably efficiently and faithfully in vitro, although the proportions of each product varied from one extract to another.

Microbial enzymes for oxidation of organic molecules

Enzymatic systems employed by microorganisms for oxidative transformation of various organic molecules include laccases, ligninases, tyrosinases, monooxygenases, and dioxygenases. Reactions performed by these enzymes play a significant role in maintaining the global carbon cycle through either transformation or complete mineralization of organic molecules. Additionally, oxidative enzymes are instrumental in modification or degradation of the ever-increasing man-made chemicals constantly released into our environment. Due to their inherent stereo- and regioselectivity and high efficiency, oxidative enzymes have attracted attention as potential biocatalysts for various biotechnological processes. Successful commercial application of these enzymes will be possible through employing new methodologies, such as use of organic solvents in the reaction mixtures, immobilization of either the intact microorganisms or isolated enzyme preparations on various supports, and genetic engineering technology.

Effect of inducers on metabolism of benzo(a)pyrene in vivo and in vitro: analysis by high pressure liquid chromatography

The characterisation of metabolites formed from benzo(a)pyrene (BP) by Aspergillus ochraceus TS and effect of inducers on BP metabolism are reported. The high pressure liquid chromatographic profile of BP metabolites was similar to that of mammalian microsomes furnishing diols, quinones and phenols. The production of BP-4,5-dihydrodiol (K-region diol) by Aspergillus ochraceus TS seems to be novel and provides first report on BP metabolism by eukaryotic fungi. In control, phenols and quinones were produced in excess over dihydrodiols while the induced preparation showed the reverse order. Presumably the induction effecting production of excess dihydrodiols influenced the synthesis of epoxide hydrolase. In addition, a differential increase in BP metabolism was observed with inducers of narrow and broad specificity.

Biotransformations of steroids

Different types of microbiological transformation of steroids are reviewed, with special attention given to bioconversions applied in the manufacturing of steroid hormones, i.e., 11 alpha- 11 beta-, 16 alpha-, 17 alpha-hydroxylations and 1-dehydrogenation. Availability and utilization of raw materials for industrial production of steroids of the estrane, androstane, and pregnane series are discussed. Among the current trends in steroid research of a practical nature, immobilization of enzymes and living cells and the spore process are emphasized as alternative techniques of steroid transformation of possible future importance. Efforts to recognize, in cell-free preparations, the components of steroid-transforming enzyme systems as well as the cellular mechanisms of control of their biosynthesis and activity are described in order to illustrate the main subjects of current basic investigation in steroid bioconversion.

Characterization of progesterone 11 alpha-hydroxylase of Aspergillus ochraceus TS: a cytochrome P-450 linked monooxygenase

The monooxygenase of Aspergillus ochraceus TS capable of 11 alpha-hydroxylation of progesterone has been resolved into three components and characterized as (i) cytochrome P450, (ii) NADPH-cytochrome P450-reductase and (iii) phosphatidyl choline. The 11 alpha-hydroxylase was observed to be NADPH dependent, and hydroxylation was enhanced by a NADPH regenerating system. This fungal monooxygenase has many features in common with that of mammalian liver microsomes. The role of mammalian cytochrome P450 inducers were tested for induction of 11 alpha-hydroxylase in Aspergillus ochraceus TS. The reductase has been partially purified.

Optimum conditions for ursodeoxycholic acid production from lithocholic acid by Fusarium equiseti M41

Ursodeoxycholic acid dissolves cholesterol gallstones in humans. In the present study optimum conditions for ursodeoxycholic acid production by Fusarium equiseti M41 were studied. Resting mycelia of F. equiseti M41 showed maximum conversion at 28 degrees C, pH 8.0, and dissolved oxygen tension of higher than 60% saturation. Monovalent cations, such as Na+, K+, and Rb+, stimulated the conversion rate more than twofold. In the presence of 0.5 M KCl, the initial uptake rate and equilibrium concentration of lithocholic acid (substrate) were enhanced by 5.7- and 1.7-fold, respectively. We confirmed that enzyme activity catalyzing 7 beta-hydroxylation of lithocholic acid was induced by substrate lithocholic acid. The activity in the mycelium was controlled by dissolved oxygen tension during cultivation: with a dissolved oxygen tension of 15% and over, the activity peak appeared at 25 h of cultivation, whereas the peak was delayed to 34 and 50 h with 5 and 0% dissolved oxygen tension, respectively. After reaching the maximum, the 7 beta-hydroxylation activity in the mycelium declined rapidly at pH 7.0, but the decline was retarded by increasing the pH to 8.0. Several combinations of operations, such as pH shift (from pH 7 to 8), addition of 0.5 M KCl, and dissolved oxygen control, were applied to the production of ursodeoxycholic acid in a jar fermentor, and a much larger amount of ursodeoxycholic acid (1.2 g/liter) was produced within 96 h of cultivation.

Induction of benzo(a)pyrene hydroxylase in Aspergillus ochraceus TS: evidences of multiple forms of cytochrome P-450

The filamentous fungus Aspergillus ochraceus TS produces an inducible microsomal cytochrome P-450 linked monooxygenase which is capable of hydroxylating benzo(a)pyrene in presence of O2 and NADPH. The addition of Benzo(a)pyrene, 3-Methyl cholanthrene, beta-Naphthoflavone and other aryl hydrocarbons during the induction period causes dramatic improvement in the kinetics of benzo(a) pyrene hydroxylation as was evidenced by large decrease in Km and increase in Vmax values. On the other hand, treatment with Phenobarbital, Polychlorinated biphenyl and Progesterone has no significant effect on the kinetics of benzo(a)pyrene hydroxylation although a significant induction of NADPH-Cyt C reductase activity was observed in all the three cases. Again, both Phenobarbital and 3-Methyl cholanthrene induced microsomes exhibit the characteristic reduced metyrapone difference spectra. These findings together with the results obtained with flavone on the metabolism of benzo(a)pyrene by various microsomal preparations suggest a parallel induction of multiple forms of cytochrome P-450 as observed in mammalian liver under identical condition.

Microsomal benzo(a)pyrene hydroxylase in Aspergillus ochraceus TS: assay and characterization of the enzyme system

Microsomal preparations of Aspergillus ochraceus TS oxidised benzo(a)pyrene very efficiently in the presence of NADPH and 02 and exhibits a pH optimum of 8.0-8.2. The hydroxylation is also effected in presence of NaI04. Hydroxylation was inhibited by metyrapone, SKF-525A, PCMB, imidazole, carbon monoxide and flavone but not by cyanide, azide and antimycin A indicating thereby the involvement of cytochrome P-450 in this reaction. Inhibition by cytochrome C is consistent with the participation of NADPH-cytochrome C reductase in this hydroxylation. Reduced microsomes and its solubilized preparation, when treated with carbon monoxide, showed absorption maxima at 453 and 449 respectively. Different classical inducers of cytochrome P-450 induce the benzo(a)-pyrene hydroxylase activity to varying degree and as such suggests the existence of multiple forms of cytochrome P-450 in this fungus.

[Steroid transformation with immobilized microorganisms]

The application of immobilized microbial cells has been receiving increasing interest, in particular because of their potential for use in industrial fermentation processes and in analytical procedures. Since the first application of an immobilized microbial biocatalyst for steroid transformation in 1970 by MOSBACH and LARSSON many results have been published concerning the use of such type of biocatalyst in steroid biochemistry and steroid microbiology, respectively. The review deals with the present scientific state of the steroid transformations performed with immobilized biocatalysts, their applications and development trends. In particular the following aspects are discussed: 1(2)-dehydrogenation or hydrogenation, hydroxylation reactions, redox processes in 3,17- and 20-oxogroups, side chain splitting of sterols, 5 alpha-reduction, modification of cholic acid derivatives and the use of immobilized plant cells. The possibility for application of microbial membrane electrodes in steroid analysis has been shown. Up to now, many results of fundamental research are known. There are possibilities for producing expensive steroid derivatives in laboratory apparatus using immobilized biocatalysts. Some of the processes, described here, are of practical interest, and some of them are said to be used industrially, respectively.