Course Of Biotransformation Research Articles

Study of biotransformation of cholesterol 3β-methyl ether by mycobacteria Mycobacterium sp.

The influence of exogenous factors on the selectivity of biotransformation of cholesterol 3β-methyl ether by Mycobacterium sp. was studied. The main product of the microbiological transformation was Δ5-dehydroepiandrosterone 3β-methyl ether. The presence of methyl-β-cyclodextrin in the bacterial growth medium led to a change in the ratio of the reaction products and an increase in the yield of Δ4-androstene-3,17-dione. Aliphatic saturated and unsaturated carboxylic acids were also formed in the course of biotransformation.

On the bi-enzymatic behaviour of Saccharomyces cerevisiae-mediated stereoselective biotransformation of 2,6,6-trimethylcyclohex-2-ene-1,4-dione

Baker’s yeast has been well-known to have the ability to reduce a variety of substrates into many optically active compounds. One of the important chemicals is (4R,6R)-4-hydroxy-2,2,6-trimethylcyclohexanone or in short, (4R,6R)-actinol, a product formed from the reduction of 2,6,6-trimethylcyclohex-2-ene-1,4-dione, (ketoisophorone). The work has successfully characterized the route of the reaction during the conversion mediated by Saccharomyces cerevisiae and it was also experimentally observed the importance of cofactor (NADH/NADPH) availability and stability during the biotransformation. The presence of cofactor has been proven to assist the product formation by keeping a continuous flow of hydrogen ions to and from the reduction system, while the amount of enzymes present determined the rate of both intermediates and product formed during the course of biotransformation. Results of the growing cells, particularly during the exponential phase of the growth significantly differ to that of the stationary phase system in terms of the formation of the intermediates and the final product. For the growing cell biotransformation, the route only stopped at the intermediate compound (4) during the course of the 30 h reaction, whereas for the stationary phase biotransformation, compound (5) was readily formed in a range of time between 2 and 12 h of reaction, depending on the amount of cells available and glucose supplied to the system. Within the yeast cell, there are two responsible enzymes that mediate the biotransformation; carbonyl reductase and enoate reductase that work both in parallel and sequential to produce a chiral alcohol of (4R,6R)-actinol.

Degradation of dyes using crude extract and a thermostable and pH-stable laccase isolated from Pleurotus nebrodensis.

Three laccase isoenzymes (Lac1, Lac2 and Lac3) have been purified to homogeneity from Pleurotus nebrodensis in our previous study. Lac2 was shown to be the dominant isoform, capable of oxidizing the majority of laccase substrates and manifesting good thermostability and pH stability. Hence, Lac2 was selected to decolourize structurally different dyes and the colour removal efficiencies of Lac2 and the crude extract of P. nebrodensis were compared. By monitoring the λmax of the reaction system during the course of biotransformation, clear hypsochromic shifts were observed for most of the dyes examined, illustrating that at least one peak disappeared as a result of laccase treatment. In general, Lac2 was more efficient within a short time (1 h) and the crude extract, in general, could achieve similar or even higher efficiency when the duration of treatment was extended to 24 h. Malachite green (MG) was chosen to study the detoxifying potential of Lac2, because of the relatively simple structure and high toxicity of the dye towards microorganisms. The toxicity of MG towards both bacteria (Bacillus subtilis, Bacillus licheniformis, Pseudomonas fluorescens and Escherichia coli) and fungi (Fusarium graminearum and Trichoderma harzianum) was dramatically decreased and the potential mechanism was estimated by GC–MS as to remove four methyl groups firstly and the two newly formed amine groups would be degraded or polymerized further. The present study facilitates an understanding of the application of P. nebrodensis laccases and furnishes evidence for the safety of their utilization in the treatment of wastewater emanating from textile industries.

Excretion of mercapturic acids in human urine after occupational exposure to 2-chloroprene

A pilot study was conducted for human biomonitoring of the suspected carcinogen 2-chloroprene. For this purpose, urine samples of 14 individuals occupationally exposed to 2-chloroprene (exposed group) and of 30 individuals without occupational exposure to alkylating substances (control group) were analysed for six potential mercapturic acids of 2-chloroprene: 4-chloro-3-oxobutyl mercapturic acid (Cl-MA-I), 4-chloro-3-hydroxybutyl mercapturic acid (Cl-MA-II), 3-chloro-2-hydroxy-3-butenyl mercapturic acid (Cl-MA-III), 4-hydroxy-3-oxobutyl mercapturic acid (HOBMA), 3,4-dihydroxybutyl mercapturic acid (DHBMA) and 2-hydroxy-3-butenyl mercapturic acid (MHBMA). In direct comparison with the control group, elevated levels of the mercapturic acids Cl-MA-III, MHBMA, HOBMA and DHBMA were found in the urine samples of the exposed group. Cl-MA-I and Cl-MA-II were not detected in any of the samples, whereas HOBMA and DHBMA were found in all analysed urine samples. Thus, for the first time, it was possible to detect HOBMA and Cl-MA-III in human urine. The mercapturic acid Cl-MA-III could be confirmed as a specific metabolite of 2-chloroprene in humans providing evidence for the intermediate formation of a reactive epoxide during biotransformation. The main metabolite, however, was found to be DHBMA showing a distinct and significant correlation with the urinary Cl-MA-III levels in the exposed group. The obtained results give new scientific insight into the course of biotransformation of 2-chloroprene in humans.

Chemoenzymatic synthesis of 2-oxabicyclo[3.3.1]nonan-3-one enantiomers via microbial reduction by Absidia coerulea AM 93

Microbial enantioselective reduction of (±)-diethyl 2-(3-oxocyclohexyl)malonate ( 1) has been described. A screening test on twenty-four fungi strains was carried out. Most of the microorganisms preferred bioreduction of (+)-isomer of δ-ketoester ( 1) to (+)- trans δ-hydroxy ester ( 2) with the anti-Prelog selectivity. Biotransformation conditions using Absidia coerulea AM 93 were optimized with respect to the growth medium, temperature and pH. An effect of 48 chemical additives on the course of biotransformation was checked. (−)-Diethyl 2-(( S)-3-oxocyclohexyl)malonate ((−)- 1) (ee = 98%) and (+)-diethyl 2-((1 R, 3 R)-3-hydroxycyclohexyl)malonate ((+)- 2) (ee = 99%) were isolated and subjected to chemical lactonization, leading to (+)-(1 R, 5 S)-2-oxabicyclo[3.3.1]nonan-3-one ((+)- 3) and (−)-(1 S, 5 R)-2-oxabicyclo[3.3.1]nonan-3-one ((−)- 3). The absolute configuration of product (−)- 1 was confirmed by comparison of its optical rotation with the literature data. The absolute configuration the carbon atom bearing hydroxyl group in product (+)- 2 was determined using the Mosher's ester.

N-demethylation of neonicotinoid insecticide acetamiprid by bacterium Stenotrophomonas maltophilia CGMCC 1.1788

Our previous study found that Stenotrophomonas maltophilia CGMCC 1.1788 could hydroxylate imidacloprid (IMI) to 5-hydroxy IMI. Here we first report that S. maltophilia CGMCC 1.1788 can demethylate acetamiprid (AAP) to form IM 2-1 that was characterized by HPLC-MS/MS and NMR. IM 2-1 retained only 10.5% contact activity and 13.1% oral activity of AAP against horsebean aphid. Time course of biotransformation under existing of sucrose revealed that 58.9% of AAP disappeared, but only 16.7% of reduced AAP was transformed to IM 2-1, after 8 days. Both demethylation and degradation of AAP contribute to the weak bioefficacy of AAP in soil application. The differences in metabolism and detoxification pathways between AAP and IMI are probably originated from the structural differences of these insecticides.

Radical accumulation in liver microsomal membranes during biotransformation of aromatic amines and nitro compounds

Accumulation of aromatic nitroxide radicals in microsomal membranes of rabbit liver has been observed by ESR-spectroscopy in the course of biotransformation of 2-acetylaminofluorene, 2-aminofluorene, 2-aminonaphthalene, 4-aminostilbene, 4,4′-diamincstilbene, 4-nitroquinoline-1-oxide.