Biomedical subjects
Publications and source records attributed to M Tanticharoen.
Bioassay-guided fractionation of the crude extract from the insect pathogenic fungus Paecilomyces tenuipes BCC 1614 led to the isolation and identification of two antimycobacterial and antiplasmodial cyclodepsipeptides, beauvericin and beauvericin A.
In this study we present the cloning and functional characterization of a gene whose product is responsible for Delta(12)-desaturase activity and is involved in the metabolic pathway of gamma-linolenic acid (GLA) synthesis of Mucor rouxii. A cDNA encoding for Delta(12)-desaturase of M. rouxii was obtained using the combination of reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification cDNA ends (RACE) techniques. The 1188 [corrected] bp code for an open reading frame of 396 amino acid residues. The deduced amino acid sequence of the cloned cDNA comprises three conserved histidine regions and two hydrophobic domains and showed similarity with microsomal omega-3 and omega-6 desaturases of plants. Expression of this open reading frame in Saccharomyces cerevisiae resulted in the accumulation of linoleic acid (C18:2), suggesting that this gene encodes for a membrane-bound desaturase, Delta(12)-desaturase, of M. rouxii that is functional in yeast.
Unsaturated fatty acids are essential lipid components of Mucor rouxii. Gamma-linolenic acid (GLA) is synthesized via the desaturase enzymes: delta9-desaturase catalyzes mono-unsaturated fatty acids that are utilized as substrate for GLA biosynthesis. We cloned and characterized a M. rouxii gene highly homologous to delta9-desaturase genes. This sequence encodes for a protein of 452 amino acids and contains two introns of 60 and 61 nucleotides. Delta9-desaturase of M. rouxii is expressed during cell growth when cells are subjected to temperature shifts. At 30 degrees C, the mRNA level of late log phase is about 6.4-fold higher than that of early log phase. A shift from 30 to 15 degrees C induced transcription of delta9-desaturase gene in both early and late log phases. However, the pattern of increased transcription by cold induction varied depending on growth conditions: transcription of late log phase is higher than that of early log phase. These results indicate that cell growth and low temperature influence the expression of delta9-desaturase gene and fatty acid composition of M. rouxii.
Bioassay-guided fractionation of an extract from the fungus Myrothecium verrucaria BCC 112 resulted in the first isolation of roridin E acetate (5) from nature together with four common macrocyclic trichothecene isomers (1-4). Trichothecenes 1-5, while known as mycotoxins, were evaluated for their high antimalarial activity.
An alkaliphilic bacterium, Bacillus sp. strain K-1, produces extracellular xylanolytic enzymes such as xylanases, beta-xylosidase, arabinofuranosidase, and acetyl esterase when grown in xylan medium. One of the extracellular xylanases that is stable in an alkaline state was purified to homogeneity by affinity adsorption-desorption on insoluble xylan. The enzyme bound to insoluble xylan but not to crystalline cellulose. The molecular mass of the purified xylan-binding xylanase was estimated to be approximately 23 kDa. The enzyme was stable at alkaline pHs up to 12. The optimum temperature and optimum pH of the enzyme activity were 60 degrees C and 5.5, respectively. Metal ions such as Fe2+, Ca2+, and Mg2+ greatly increased the xylanase activity, whereas Mn2+ strongly inhibited it. We also demonstrated that the enzyme could hydrolyze the raw lignocellulosic substances effectively. The enzymatic products of xylan hydrolysis were a series of short-chain xylooligosaccharides, indicating that the enzyme was an endoxylanase.
The amperometric determination of sulfite was performed using copper electrodes in alkaline media. A mechanism for the oxidation of sulfite at these electrodes is suggested, based on the formation of superficial CuO(.OH), which acted as an electron transfer mediator to the analyte. At 0.5 V versus SCE in 1 M NaOH, sulfite could be calibrated at a sensitivity of 0.2 A l mol-1 cm-2, with a response time for the steady state of 30 s. The limit of detection (three times the signal-to-noise ratio) was 2.5 x 10(-6) M and the response was linear up to 5 x 10(-4) M (r2 = 0.9996, n = 15). The standard deviation (n = 10) at 1 x 10(-5) and 1 x 10(-4) M was 3.27 x 10(-7) A cm-2 (mean = 3.62 x 10(-6) A cm-2) and 1.07 x 10(-13) A cm-2 (mean = 2.25 x 10(-5) A cm-2), respectively.