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Biomedical subjects

G T Tsao

Publications and source records attributed to G T Tsao.

At least 19 recordsLinked to original sources
PubMed1998

Production of L-malic acid via biocatalysis employing wild-type and respiratory-deficient yeasts.

The yeast Saccharomyces cerevisiae has been used to efficiently produce L-malic acid from fumaric acid. Fumarase is responsible for the reversible conversion of fumaric and L-malic acids in the TCA cycle. To investigate the function of mitochondrial and cytoplasmic fumarase isoenzymes in L-malic acid bioconversion, a wild-type strain and a cytoplasmic respiratory-deficient mutant devoid of functional mitochondria were employed. The mutant strain, which only contained the cytoplasmic fumarase, was still functional in fumaric acid to L-malic acid bioconversion However, its specific conversion rate was much lower (0.20 g/g.h) than that of the wild-type strain (0.55 g/g.h).

Catalysis↗
PubMed1998

Bioconversion of fumaric acid to succinic acid by recombinant E. coli.

Succinic acid was produced efficiently from fumaric acid by a recombinant E. coli strain DH5 alpha/pGC1002 containing multicopy fumarate reductase genes. The effects of initial fumaric acid and glucose concentration on the production of succinic acid were investigated. Succinic acid reached 41 to over 60 g/L in 48.5 h starting with 50 to 64 g/L fumaric acid. Significant substrate inhibition was observed at initial fumaric acid concentration of 90 g/L. L-Malic acid became the major fermentation product under these conditions. Provision of glucose (5-30 g/L) to the fermentation medium stimulated the initial succinic acid production rate over two folds.

Acetic Acid↗
PubMed1996

Pretreatment of sugar cane bagasse hemicellulose hydrolysate for xylitol production by yeast.

A total of six known xylitol-producing yeast strains were screened for production of xylitol from xylose. Candida sp. 11-2 proved to be the best producer. It was chosen to study its ability to produce xylitol from hemicellulose hydrolysate derived from sugar cane bagasse. The hydrolysate was prepared by dilute sulfuric acid (2-3% [w/v]) hydrolysis, with a high-solid, low-liquid ratio followed by leaching. Owing to the inhibitors present in the hydrolysate, different treatments were studied to overcome its effect. In order to reach higher xylitol productivity, treated hydrolysates were concentrated by vacuum evaporation in rotavapor to provide a higher initial xylose concentration. After treatment, Candida sp. 11-2 was able to ferment xylose in hemicellulose hydrolysate to produce xylitol.

Charcoal↗
PubMed1996

Improvement of productivity of yeast cell with a novel airlift loop reactor.

Two different strains of baker's yeast are cultivated using a fed-batch process with a novel airlift loop reactor. The reactor can be operated not only under steady-state conditions as the traditional airlift loop reactor, but also under forced periodically operational conditions in which the direction of liquid circulating flow is alternatively changed. Compared with the traditional steady-state operation, both the growth rate and yield of cells are much higher in the forced periodic operation.

Biotechnology↗
PubMed1990

Purification, characterization, and amino terminal sequence of xylose reductase from Candida shehatae.

D-Xylose is a major component of the carbohydrates derived from agricultural residues and forest products. Among more than two hundred known xylose-utilizing yeasts, only a few species are known to be able to ferment xylose anaerobically. Candida shehatae is one of such xylose-fermenting yeasts. Xylose reductase (E.C. 1.1.1.21) is a key enzyme responsible for xylose metabolism in xylose-utilizing as well as xylose-fermenting yeasts. In this paper, we report the development of a convenient and reliable procedure for the purification of xylose reductase from C. shehatae to near homogeneity. The amino acid composition and N-terminal sequence of the enzyme have also been analyzed. C. shehatae seems to contain only a single xylose reductase, but the enzyme has a dual coenzyme specificity for both NADPH and NADH. The enzyme is remarkably stable at room temperature and 4 degrees C.

Aldehyde Reductase↗
PubMed1982

Sequential utilization of mixed monosaccharides by yeasts.

Four yeasts (Saccharomyces cerevisiae, Schizosaccharomyces pombe, Candida utilus, and Rhodotorula toruloides) were tested for their ability to grow and consume D-glucose, D-xylose, D-xylulose, and D-xylitol. Sequential utilization of substrates was observed when D-glucose as mixed with D-xylulose as the carbon source. Catabolite inhibition was tentatively concluded to be responsible for this regulatory mechanism. D-Glucose was also found to inhibit the utilization of D-xylose and D-xylitol in C. utilus and R. toruloides. D-Xylose, D-xylitol, and D-xylulose were consumed simultaneously by R. toruloides and C. utilus.

Ascomycota↗
PubMed1979

Affinity chromatography of endoglucanase of Trichoderma viride by concanavalin A-agarose.

Endoglucanase (C kappa cellulase) and cellobiase are often cross-contaminated in separation procedures by ion-exchange chromatography such as DEAE-cellulose. By using concanavalian A (Con A)-agarose chromatography, C kappa cellulase and cellobiase from Trichoderma virde can be separated. C kappa cellulase showed affinity toward Con A. indicating a glycoprotein containing alpha-D-mannopyransyl and alpha-D-glucopyranosyl end groups or internal 2-O-D-mannopyranosyl residues in sugar moieties. This method provides a way to estimate the quantities of C kappa enzyme produced by T. viride and possibly by other organisms.

Binding Sites↗
PubMed1979

Convenient method for studying enzyme kinetics.

A convenient method for enzyme kinetic studies is introduced. The method includes identification of reaction mechanism and estimation of the associated kinetic constants with a minimum number of experiments. The application of the method is illustrated by using literature data. Factors limiting the application of this method are also discussed.

Binding, Competitive↗
PubMed1978

Formaldehyde incorporation by a new methylotroph (L3).

A number of bacterial strains have been isolated and investigated in our search for a promising organism in the production of single-cell protein from methanol. Strain L3 among these isolates was identified as an obligate methylotroph which grew only on methanol and formaldehyde as the sole sources of carbon and energy. The organism also grew well in batch and chemostat mixed-substrate cultures containing methanol, formaldehyde, and formate. Although formate was not utilized as a sole carbon and energy source, it was readily taken up and oxidized by either formaldehyde- or methanol-grown cells. The organism incorporated carbon by means of the ribulose monophosphate pathway when growing on either methanol, formaldehyde, or various mixtures of C1 compounds. Its C1-oxidation enzymes included phenazine methosulfate-linked methanol and formaldehyde dehydrogenase and a nicotinamide adenine dinucleotide-linked formate dehydrogenase. Identical inhibition by formaldehyde of the first two dehydrogenases suggested that they are actually the same enzyme. The organism had a rapid growth rate, a high cell yield in the chemostat, a high protein content, and a favorable amino acid distribution for use as a source of single-cell protein. Of special interest was the ability of the organism to utilize formaldehyde via the ribulose monophosphate cycle.

Alcohol Oxidoreductases↗
PubMed1977

Characteristics of yeast invertase immobilized on porous cellulose beads.

Invertase from Candida utilis was immobilized on porous cellulose beads by an ionic-quanidino bond. The immobilized invertase showed optimum activity between pH 4.0 and 5.4, while the free enzyme had a sharp optimum at pH 4.1. Both temperature profiles were fairly similar up to 55 degrees C. However, above this temperature the immobilized enzyme was more stable than the free enzyme. From the temperature data, the activation energies were found to be 7,322 and 4,052 cal/g mol for the free and the immobilized enzyme, respectively. Candida invertase shows characteristics of substrate inhibition. Both the Km and Ki for the free and the immobilized enzymes were determined. The apparent Ki for the immobilized invertase was much higher than the Ki of the free enzyme, suggesting a diffusion effect. Immobilized invertase molecules deep in the pores only see sucrose concentrations much less than the bulk concentrations. Immobilization, thus, offers certain processing advantages in this regard.

Candida↗
PubMed1977

Cellobiase from Trichoderma viride: purification, properties, kinetics, and mechanism.

Three distinct cellobiase components were isolated from a commercial Trichoderma viride cellulase preparation by repeated chromatography on DEAE cellulose eluting by a salt gradient. The purified cellobiase preparations were evaluated for physical properties, kinetics, and mechanism. Results from this work include: 1) development of one step enzyme purification procedure using DEAE-cellulose; 2) isolation of three chromatographically distinct, yet kinetically similar, cellobiase fractions of molecular weight of approximately 76,000; 3) determination of kinetics which shows that cellobiase hydrolyzes cellobiose by a noncompetitive mechanism and that the product, glucose, inhibits the enzyme, and 4) development of an equation, based on the mechanism of cellobiase action, which accurately predicts the time course of cellobiose hydrolysis over an eightfold range of substrate concentration and conversions of up to 90%. Based on the data presented in the paper, it is shown that product inhibition of cellobiase significantly retards the rate of cellobiose hydrolysis.

Disaccharides↗
PubMed1977

Chemical procedures for enzyme immobilization on porous cellulose beads.

In a previous article, the method of preparation and the physical properties of porous (75 to 80% porosity) cellulose beads were described (Biotechnol. Bioeng., 18, 1057 (1976). The present article reports that the chemical procedures employed for immobilizing enzymes on ordinary cellulose can be applied to the porous cellulose beads. The results showed more enzyme loading on the beads than ordinary cellulose. The choice of the procedures might also affect the mechanical strength of the cellulose beads.

Carbohydrate Epimerases↗
PubMed1977

Growth characteristics of a new methylomonad.

A methylomonad culture was isolated from pond water and examined as a potential source of single-cell protein. A medium containing magnesium sulfate, ammonium hydroxide, sodium phosphate, tap water, and methanol supported the growth of the isolate. Optimal growth conditions in batch cultures for the organism were: temperature, 30 to 33 degrees C; pH 7.1; and phosphate concentration, 0.015 M. The minimum doubling time obtained was 1.6 h. The specific growth rate in batch culture was dependent on the methanol concentration, reaching a maximum around 0.2% (wt/vol). Growth inhibition was apparent above 0.3% (wt/vol), and growth was completely inhibited above 4.6% (wt/vol) methanol. Although the inhibitory effect of formaldehyde on the specific growth rate was much greater than that of formate, the organism utilized formaldehyde, but not formate, as a sole carbon and energy source in batch cultures. The isolate was identified primarily by its inability to utilize any carbon source other than methanol and formaldehyde for growth. Although it is capable of rapid growth on methanol, the organism showed a very weak catalase activity. The amino acid content of the cells compared favorably with the reference levels for the essential amino acids specific by the Food and Agricultural Organization of the United Nations.

Amino Acids↗
PubMed1976

Pilot plant production of glucose with glucoamylase immobilized to porous silica.

Glucoamylase was immobilized to porous silica and its kinetics and stability were observed with acid- and alpha-amylase-hydrolyzed dextrin as feed. The enzyme was found to be extremely stable in both laboratory and pilot plant operations. When the feed had been previously only lightly hydrolyzed, pore diffusion limitation caused appreciable decreases in glucose production rate. The severity of starch hydrolysis to dextrin markedly affected ultimate glucose yields. The diffusional gradients present in the carrier pores caused the immobilized enzyme to yield lower glucose concentrations than the free enzyme at similar feed conditions.

Glucose↗