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Biomedical subjects

I Miwa

Publications and source records attributed to I Miwa.

At least 91 records · Page 5Linked to original sources
PubMed1986

Anomeric preference of glucose phosphorylation and glycolysis in human erythrocytes.

Lactate output from the alpha and beta anomers of glucose was measured in intact human erythrocytes at 37 degrees C; and glucose anomer phosphorylation, in human erythrocyte homogenates. The rates of both glucose metabolism (lactate output) and phosphorylation were higher in the presence of beta-D-glucose as distinct from alpha-D-glucose at three glucose concentrations used (2, 5, and 10 mM). Thus, the v beta/v alpha ratios of metabolism and phosphorylation of glucose at 2 mM were 1.24 and 1.22, respectively. The results indicate that the beta preference of hexokinase, a rate-limiting enzyme in glycolysis, is reflected in beta-preferential glycolysis.

Blood Glucose↗
PubMed1985

Inhibition of glucose-stimulated insulin release by pseudo-alpha-DL-glucose as a glucokinase inhibitor.

Pseudo-alpha- and pseudo-beta-DL-glucose, the isomers of 5-hydroxymethyl-1,2,3,4-cyclohexanetetrol with alpha-gluco and beta-gluco configurations, were used as synthetic analogs of glucose anomers to study the mechanism of glucose-stimulated insulin release by pancreatic islets. Neither isomer was phosphorylated by liver glucokinase nor stimulated insulin release from islets. Incubation of islets with pseudo-alpha-DL-glucose resulted in a considerable accumulation of the glucose analog, probably the D form, in islets. The alpha-isomer, but not the beta-isomer, inhibited both glucose-stimulated insulin release (44% inhibition at 20 mM) and islet glucokinase activity (36% inhibition at 20 mM) in a concentration-dependent manner and to a comparable degree. These results strongly suggest that the inhibition of glucose-stimulated insulin release by pseudo-alpha-DL-glucose is due to the inhibition of islet glucokinase by the glucose analog, providing additional evidence for the essential role of islet glucokinase in glucose-stimulated insulin release.

Animals↗
PubMed1984

Affinity of mutarotase for Sephadex and glycogen.

It was found that hog kidney mutarotase has an affinity for Sephadex G-100, equilibrated and eluted with 5 mmol/l EDTA buffer (pH 7.4), resulting in retardation of its elution from the column. The affinity was reduced depending upon the presence of 0.15 mol/l NaCl and 0.2 mol/l glucose, separately or in combination. A small portion of mutarotase was adsorbed to rabbit liver glycogen as judged from the column chromatography of a mixture of the two on Bio-Gel P-100. Mutarotase was adsorbed to neither dextran nor raw potato starch.

Animals↗
PubMed1984

D-glucose anomeric preference of hexokinases from animals and yeast.

The D-glucose anomeric preference of hexokinases partially purified from animals (rat, mouse, and chicken) and baker's yeast (Saccharomyces cerevisiae) were investigated by the assay system with glucose-6-phosphate dehydrogenase as a coupling enzyme. With low Km hexokinases in animal tissues and cells, the ratios of Vmax for the beta-anomer to Vmax for the alpha-anomer (V beta/V alpha) were within a range from 1.3 to 1.5. In yeast, the V beta/V alpha value was 1.1 for hexokinase A, 0.8 for hexokinase B, and 1.4 for glucokinase. The possible explanation for D-glucose anomeric preference of hexokinase is discussed.

Animals↗
PubMed1984

Destruction of immaturin activity in early mature mutants of Paramecium caudatum.

Cells of Paramecium in the sexually immature period of the clonal life cycle contain a protein called immaturin, which represses mating activity when injected into sexually mature cells. The amount of immaturin at various stages of the immaturity period was examined by injecting cytoplasm from immature cells of one wild-type and two early mature mutant clones into mature cells of wild-type. The proportion of immature cells brought about by the injection increased until about 10-15 fissions after conjugation of the donor cells in all three clones. But the percentage of immature cells induced by the injection decreased rapidly from the 25th to the 30th fission of both early mature donors, while the percentage was still high with a wild-type donor of the same fission age. When cytoplasm of the Emt A (early mature mutant) homozygote taken immediately before maturation (about 27 fissions) was injected into the wild-type immature cells of 45 fissions after conjugation, 13% of the recipient cells expressed mating reactivity. But when cytoplasm of Emt A cells 20 and 50 fissions after conjugation was injected into the same cells, no reactive cell appeared. The results suggest that cytoplasm of the early mature mutant immediately before maturation contains some material that accelerates maturation when injected into wild-type cells in the late stage of immaturity. On the other hand, the immature cytoplasm of wild-type cells about 25 fissions after conjugation showed no effect when injected into early mature cells immediately before maturation. The function of the early mature gene product was suggested to be the destruction of immaturin activity.

Animals↗
PubMed1984

Inhibition of glucokinase in hepatocytes by alloxan.

The effect of alloxan on glucokinase in isolated rat hepatocytes was studied. Exposure of hepatocytes to alloxan (3 mM) at 30 degrees C for 5 min produced a marked inhibition (77%) of glucokinase activity and altered slightly the phosphofructokinase activity (32% inhibition). Pyruvate kinase and glucose 6-phosphate dehydrogenase, however, were not inhibited at all. Alloxan induced a concentration-dependent inhibition of glucokinase activity with a detectable inhibition at an alloxan concentration of 1 mM. The inhibition of glucokinase activity by alloxan was protected by the simultaneous presence of 15 mM hexose such as D-glucose, 3-O-methylglucose, or D-mannose. D-Galactose showed no protective effect. These results suggest that alloxan may exert its cytotoxic action through the inhibition of glucokinase activity not only in the liver but also in the pancreatic islets, since liver and islet glucokinases are known to be quite similar in various properties.

Alloxan↗
PubMed1983

Multiple forms of mutarotases from the kidney, liver, and small intestine of rats: purification, properties, subcellular localization and developmental changes.

Comparative studies of mutarotase [aldose 1-epimerase, EC 5.1.3.3] from the kidney, liver and small intestine of rats were performed placing in the focus on the study of multiple forms. The findings obtained are as follows. Mutarotases from the kidney and liver of adult rats were both separated into four forms (types I-IV) by DEAE-cellulose column chromatography, whereas only two forms (types I and II) were detected in the small intestine. Liver mutarotase type I was further separated into types I1 and I2 by column chromatography on hydroxylapatite. Types I and II from the kidney and type II from the liver were purified to homogeneity as judged by isoelectric focusing on thin layer polyacrylamide gel. Of various physicochemical properties, only the Km for alpha-D-xylose and the isoelectric point were different among the multiple forms. Liver mutarotase was immunohistochemically localized in the nuclei of parenchymal cells and small intestine enzyme in the nuclei of mucosal cells, indicating similarity with the localization of kidney enzyme (in the nuclei of epithelial cells of renal tubules and glomeruli) which was reported in our previous paper [Experientia (1979) 35, 1094-1097]. The kidney mutarotase level increased gradually after birth and reached a maximum near adult level within 20 days. This developmental pattern was essentially the same as that in the liver but clearly different from that in the small intestine, in which the mutarotase activity of suckling rats was several times higher than that of adult rats. Distribution patterns of multiple forms (types I-IV) of the enzyme in the kidney and liver of 10-day-old rats were similar to those in respective tissues of adult rats. On the other hand, the small intestine of 10-day-old rats contained four forms (types I-IV), whereas there were only two forms (types I and II) in adult rats.

Aging↗
PubMed1983

Preference of glucokinase for the alpha anomer of hexose: relation to alpha-anomer preference in hexose-induced insulin release by pancreatic islets.

The alpha anomers of glucose and mannose were more rapidly phosphorylated than the beta anomers by rat liver glucokinase, whose chromatographic and kinetic properties are known to be quite similar to those of pancreatic islet glucokinase. This result may explain our previous findings of the alpha-anomeric preference in glucose- and mannose-stimulated insulin release, and therefore suggests to support the hypothesis that glucokinase in islets functions as a crucial hexose sensing enzyme for insulin release induced by glucose and mannose.

Animals↗
PubMed1982

Inhibition of aldose reductases from rat and bovine lenses by flavonoids.

Thirty flavones, four isoflavones and thirteen coumarins were tested as inhibitors of lens aldose reductase, which is believed to participate in the initiation of cataract formation in diabetes. Many were found to be potent inhibitors, and the two most potent ones were axillarin (5,7,3',4'-tetrahydroxy-3,6-dimethoxyflavone) and 6,3',4'-trihydroxy-5,7,8-trimethoxyflavone (LARI 1). These two flavones inhibited aldose reductase purified from rat lens with IC50 values of 2.6 X 10(8) and 3.6 X 10(8) M respectively. They also inhibited aldose reductase purified from bovine lens with IC50 values of 1.8 X 10(7) M. The potencies of the two compounds were superior to those of all the previously reported inhibitors of aldose reductase. Inhibition of rat and bovine lens aldose reductases by the two compounds was of a non-competitive type with DL-glyceraldehyde as the variable substrate. Some flavones including axillarin and LARI 1 were found to be poorly or scarcely inhibitory against several adeninenucleotide-requiring enzymes, which are involved in glycolysis and other metabolic reactions. These results obtained show that the two flavones have some features which may be required in clinically useful drugs for diabetic patients. All the potent inhibitors of the compounds tested had a flavone skeleton, one (or two free) hydroxyl(s) in ring C, and more than three hydroxyls (free or methylated) in ring A. The possible relationships of structures to inhibitory potencies of the compounds tested are discussed.

Aldehyde Reductase↗
PubMed1982

Non-enzymatic reduction of alloxan by reduced nicotinamide nucleotide.

Much evidence has been reported that the diabetogenic action of alloxan is caused by the formation of cytotoxic free radicals during the autoxidation of dialuric acid, a reduction product of alloan, to alloxan. The mechanism by which alloxan is reduced in vivo to dialuric acid, however, is unknown. The non-enzymatic reaction of alloxan with NAD(P)H was studied as a possible candidate for the reduction of alloxan. The reaction was carried out at 37 degrees in 50 mM phosphate buffer (mostly at pH 7.0) and was followed by measuring the decrease in absorbance at 340 nm. NADH and NADPH were found to be stoichiometrically oxidized by alloxan to NAD and NADP respectively. When the alloxan concentration (1.0 mM) was kept constant and the concentration of NAD(P)H (0.05 to 0.2 mM) was varied, the rate of decrease in the relative concentration of NAD(P)H was almost constant, suggesting that the autoxidation of dialuric acid by O2 was rapid enough to neglect its presence in the medium. The reaction between alloxan and NAD(P)H was accelerated by decreasing the pH. Both the rate of decrease in NAD(P)H concentration and the rate of O2 consumption resulting from autoxidation of the dialuric acid formed by reduction of alloxan were not affected by the presence of 20 mM D-glucose. Ethylene formation by the reaction of methional with . OH, one of the autoxidation products of dialuric acid, was clearly reduced by the presence of alpha- or beta-D-glucose (20 mM), but there was no significant difference between the effects of the two anomers. These results with D-glucose ruled out the possibility that the protection of beta-cells by D-glucose against the diabetogenicity of alloxan can be explained either by its inhibitory action on dialuric acid formation or by its scavenging effect on . OH.

Alloxan↗
PubMed1982

Purification and characterization of multiple forms of mutarotase from hog kidney cortex.

The enzyme mutarotase [aldose 1-epimerase, EC 5.1.3.3] from hog kidney cortex was separated into four fractions (designated types I, II, III, and IV in order of elution) by column chromatography on DEAE-cellulose. Two major forms, types I and II, were purified to homogeneity as judged by polyacrylamide gel electrophoresis and isoelectric focusing on thin layer polyacrylamide gel. Types I, II, III, and IV had isoelectric points of 5.78, 5.48, 5.23, and 5.10, respectively. The following physicochemical properties were common to all four types: molecular weight, 41,000; Km for alpha-D-glucose at pH 7.4 and 25 degrees C, 19 mM; optimum pH, 6.5-7.5; optimum temperature, 30-37 degrees C; heat stability, up to 50 degrees C. On double immunodiffusion, the four types of mutarotase gave single precipitin lines, which fused completely with each other, against the antibody to purified type II enzyme. Types I and II had an identical amino-terminal residue, arginine, and an identical carboxyl-terminal sequence, -(Phe-Phe-Ser-Val)-Val-Ala. The amino acid composition of type I was almost identical with that of type II. Very similar tryptic peptide maps were obtained from types I and II, with only a few points of variance. These results suggest that the four types of hog kidney mutarotase are quite similar but not identical.

Amino Acids↗