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G Okada

Publications and source records attributed to G Okada.

At least 19 recordsLinked to original sources
PubMed1992

Non-transformed, but not ras/myc-transformed, serum-free mouse embryo cells recover from growth suppression by azatyrosine.

The anti-proliferative effect of azatyrosine, a newly discovered antibiotic from Streptomyces, was examined in Balb/c-originated serum-free mouse embryo (SFME) cells and transformed ras/myc SFME cells which have activated human c-Ha-ras genes. Azatyrosine suppressed their growth in a concentration-dependent manner. Growth suppression in both cells was detectable within 2 days after culture with 250 micrograms/ml azatyrosine. Non-transformed SFME cells, however, regained rapid growth after 6 days even in the presence of azatyrosine, whereas ras/myc SFME cells did not recover from the suppression. Despite the growth inhibition of ras/myc SFME cells, expression of human ras in the cells was not inhibited by azatyrosine. Meanwhile, SFME cells have the ability to express glial fibrillary acidic protein (GFAP). This expression is induced by serum-supplemented medium, though the serum inhibits the growth of SFME cells. Azatyrosine did not induce GFAP in ras/myc SFME cells, but inhibited growth. Furthermore, azatyrosine did not induce GFAP in SFME cells, and had no effect upon the expression of GFAP induced by serum in these cells. These results suggest that azatyrosine inhibited the growth of ras/myc SFME cells through a mechanism independent of those involved in growth inhibition and induction of GFAP expression by serum in SFME cells.

Alanine↗
PubMed1988

Stereochemical studies of D-glucal hydration by alpha-glucosidases and exo-alpha-glucanases: indications of plastic and conserved phases in catalysis by glycosylases.

Alpha-Glucosidases from Aspergillus niger, pig serum, ungerminated rice, buckwheat, and sugar beet seeds (but not from brewers' yeast or honeybee) were found to catalyze the hydration of D-glucal. Each reactive alpha-glucosidase, incubated with D-glucal in D2O, was shown to protonate (deuteriate) this prochiral substrate from above its re face, i.e., from a direction opposite that assumed for protonating alpha-D-glucosidic substrates. At the same time, D-glucal hydration catalyzed by three of the alpha-glucosidases that acted rapidly enough in D2O to determine product configuration was found to yield 2-deoxy-D-glucose of the same specific (alpha-) configuration as the D-glucose produced from alpha-D-glucosidic substrates. These findings substantially extend those reported earlier for the hydration of D-glucal by one (Candida tropicalis) alpha-glucosidase preparation. Together with other recent results, they suggest that the process of catalysis by alpha-glucosidases (and perhaps glycosylases in general) may comprise two separate and separately controlled parts, namely, a "plastic" phase concerned with substrate protonation and a substrate-unrelated "conserved" phase concerned with the creation of product configuration. In contrast to the alpha-glucosidases, three "inverting" exo-alpha-glucanases (Arthrobacter globiformis glucodextranase; Rhizopus niveus and Paecilomyces varioti glucoamylase) were found to protonate D-glucal from below its si face. Further, whereas the catalysis of D-glucal hydration by the alpha-glucosidases was intensively inhibited by excess substrate, that promoted by the exo-glucanases showed no detectable substrate inhibition.

Animals↗
PubMed1987

Partial and complete adenine phosphoribosyltransferase deficiency associated with 2,8-dihydroxyadenine urolithiasis: kinetic and immunochemical properties of APRT.

We have studied adenine phosphoribosyltransferase (APRT) in the hemolysates from the families of 2,8-dihydroxyadenine urolithiasis associated with partial deficiency of APRT (the Japanese type) and complete deficiency of APRT (the null type). The APRT in the control subjects was found to be heat-stable at the physiological concentration of phosphoribosylpyrophosphate (PRPP), which was close to the value of its Km for PRPP. The APRT in the Japanese type showed 10 times higher Km values for PRPP and needed a comparably increased level of PRPP for stability in vitro. No change in red cell PRPP was found in the Japanese type of APRT deficiency. The content of APRT enzyme protein was decreased in the hemolysates of the Japanese type, probably due to its lability at the level of PRPP present in the cells. The heterozygote of the null type also had labile enzyme molecules at the physiological PRPP concentration.

Adenine↗
PubMed1986

Purification and characterization of adenine phosphoribosyltransferase from mouse mammary carcinoma FM3A cells in culture.

Adenine phosphoribosyltransferase has been purified to apparent homogeneity from mouse mammary tumor FM3A cells. The purified enzyme, with a specific activity of 20.6 X 10(6) units/g protein at 30 degrees C, was homogeneous as judged by polyacrylamide gel electrophoresis and Ouchterlony double immunodiffusion analysis. The native enzyme had a molecular weight of 44,000 and a subunit composition of 23,000. Apparent Km values for adenine and 5-phosphoribosyl-1-pyrophosphate (PRib-PP) were 6.6 microM and 1.2 microM, respectively. Free Mg2+ was an essential activator with a half-maximal effect at 0.4 mM. AMP was an inhibitor, competitive with PRib-PP, and the Ki value was estimated to be 24 microM. The enzyme activity was not significantly affected by 2,6-diaminopurine, 4-carbamoylimidazolium 5-olate, 8-azaadenine, and 2-fluoro-6-aminopurine. An antibody against the purified mouse adenine phosphoribosyltransferase was raised in a rabbit. The enzyme derived from either mouse, Chinese hamster, or human cells was completely neutralized and precipitated by this antibody, indicating that these enzymes share a common antigenic determinant.

Adenine Phosphoribosyltransferase↗
PubMed1986

Hydration of cellobial by exo- and endo-type cellulases: evidence for catalytic flexibility of glycosylases.

New insight has been obtained into the catalytic capabilities of cellulase. Essentially homogeneous preparations of exo- (or Avicelase-) type and endo- (or CMCase-) type cellulases from Irpex lacteus and Aspergillus niger, respectively, were shown to hydrate the enolic bond of cellobial to form 2-deoxycellobiose. The A. niger enzyme also synthesized a small amount of a 2-deoxycellobiosyl-transfer product from cellobial. By use of digests conducted in deuterated buffer and 1H NMR spectra for product analysis, both cellulases were found to protonate (deuterate) the double bond of cellobial from below the si face of the D-glucal moiety, i.e., from a direction opposite that assumed for protonation of the beta-D-glycosidic linkages of cellulose and cellodextrins. The exo enzyme, which hydrolyzes the latter substrates primarily to cellobiose, rapidly catalyzed cellobial hydration to produce the beta-anomer of beta-D-glucopyranosyl(1----4)-2-deoxy-D-glucose-2(e)-d. The A. niger cellulase produced the same 2-deoxycellobiose-d from cellobial, though too slowly for its configuration to be determined. However, evidence was obtained for the formation of a beta-2-deoxycellobiosyl-d-D-glucose-transfer product by the enzyme. Thus, it is likely that all of the observed reactions with cellobial represent trans additions at the double bond. In any case, the anomeric configuration of products is created de novo. Separate mechanisms are described for the reaction of cellobial hydration and for the stereochemically different reaction of cellulose hydrolysis catalyzed by the present enzymes, assuming an arrangement of their catalytic groups analogous to that found in lysozyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspergillus niger↗
PubMed1985

[Beta-amylase].

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Amylases↗
PubMed1985

[Glucoamylase].

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Glucan 1,4-alpha-Glucosidase↗
PubMed1985

[Pullulanase].

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Enterobacter↗
PubMed1985

[Isoamylase].

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Glycoside Hydrolases↗
PubMed1979

The predominantly nonhydrolytic action of alpha amylases on alpha-maltosyl fluoride.

Crystalline alpha amylases from a number of sources utilized alpha-maltosyl fluoride as a glycosyl donor and acceptor at high rates (approximately 10 to approximately 1550 mumol/min/mg of protein, for 30 mM substrate). All enzymes catalyzed conversion of this compound into maltooligosaccharides in preference to causing its hydrolysis. Maltotetraosyl flouride and maltooligosaccharides of d.p. 3 to 6+ accounted for 75--93% (by weight) of early reaction-products. At a late stage, the yield of maltooligosaccharides was 2--5 times that of maltose, with chains as long as 12 D-glucosyl residues formed by one amylase (from Asp. oryzae), which utilized alpha-maltosyl fluoride as a donor and as an acceptor at extremely high rates. These results indicate that alpha amylases have a substantial capacity for binding two molecules of this small substrate in a distinctive way, with the C--F glycosylic bond of one and the free C-4 hydroxyl group of the other located in the region of the enzyme's catalytic groups, therby favoring glycosylation of the suitably positioned acceptor over solvent water. Hydrolysis is assumed to prevail when only a single substrate molecule or segment binds to alpha amylase with a (1 linked to 4)-alpha-D-glucosidic linkage of glycosylic C--F bond positioned at the catalytic center. The present demonstration that glycosyl-transfer reactions can be dominantly expressed by alpha amylases, given an appropriate substrate, illustrates the inadequacy of the usual characterization of these enzymes as hydrolases that produce overwhelming hydrolysis of all substrates.

Amylases↗
PubMed1976

Enzymatic studies on a cellulase system of Trichoderma viride. IV. Purification and properties of a less-random type cellulase.

A cellulase [EC 3.2.1.4] component was purified from a crude cellulase preparation of Trichoderma viride (Meicelase) by consecutive column chromatography procedures, and was designated as cellulase III. The enzyme was homogeneous on polyacrylamide gel disc electrophoresis. The molecular weight of the enzyme was estimated to be about 45,000 by gel filtration. The optimum pH and temperature of the enzyme were pH 4.5-5.0 and 50 degrees, respectively. The enzyme was stable over the range of pH 4.5-7.5 at 4 degrees for 24 hr, and retained 40% of the original carboxymethylcellulose-saccharifying activity after heating at 100 degrees for 10 min. The enzyme was completely inactivated by 1 mM Hg2+, and partially by 1 mM Ag+ and Cu2+. The enzyme was characterized as a less-random type cellulase on the basis of its action on carboxymethylcellulose. The enzyme split cellohexaose, retaining the beta-configuration of the anomeric carbon atoms in the hydrolysis products. The Km values of cellulase III for cellooligosaccharides decreased in parallel with increase of the chain length of the substrates, while Vmax values showed a tendency to increase. The enzyme produced predominantly cellobiose and glucose from various cellulosic substrates as well as from higher cellooligosaccharides. Cellulase III preferentially attacked the aglycone linkage of p-nitrophenyl beta-D-cellobioside. The enzyme was found to catalyze the rapid synthesis of cellotetraose from cellobiose (condensation action).

Carboxymethylcellulose Sodium↗