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Biomedical subjects

T Yubisui

Publications and source records attributed to T Yubisui.

At least 73 records · Page 4Linked to original sources
PubMed1982

Cytochrome reductase activities in rat brain microsomes during development.

Postnatal developmental alterations of microsomal NADH-cytochrome b5 reductase and NADPH-cytochrome c reductase activities were determined in the brain of rats. The reductase activities increased from a low level in the immature brain to a maximum level at 23 to 30 days of age, and then decreased slightly to a plateau. The periods of the activity increments were in accord with those of the enhancement of microsomal fatty acid elongation. The specific activities of these reductases were high in cerebral hemispheres and medulla oblongata, intermediate in midbrain, and lowest in cerebellum of the four regions of 20-day-old rat brain.

Animals↗
PubMed1982

Alteration of NADH-diaphorase and cytochrome b5 reductase activities of erythrocytes, platelets, and leucocytes in hereditary methaemoglobinaemia with and without mental retardation.

NADH-diaphorase and cytochrome b5 reductase activities of platelets and leucocytes, as well as erythrocytes, were found to be deficient in a patient with hereditary methaemoglobinaemia associated with moderate mental retardation and non-progressive neurological disturbance, in which hyperactive reflexes and involuntary movements were notable. In another methaemoglobinaemic patient with no mental or neurological abnormalities, these enzyme activities were defective in erythrocytes but normal in platelets and leucocytes. The first case was a generalised cytochrome b5 reductase deficiency with non-progressive encephalopathy. It is suggested that the detection of cytochrome b5 reductase activity in platelets, in addition to that in leucocytes, is useful for the assessment of a generalised enzyme defect. Genetical involvement of the present cases is discussed in association with the diaphorase gene loci in humans.

Adolescent↗
PubMed1980

Stopped flow studies on the nonenzymatic reduction of methemoglobin by reduced flavin mononucleotide.

The nonenzymatic reduction of methemoglobin by the reduced form of flavin mononucleotide was studied under various conditions by following the reaction with a stopped flow apparatus. The reaction was very fast, compared with the reduction of the flavin by NADPH-flavin reductase of human erythrocytes, and followed a second order rate law: the rate constant (K) for the reduction of methemoglobin by reduced flavin mononucleotide was determined to be 5.5 X 10(6) M-1 S-1 in 50 mM phosphate buffer (pH 7.0) at 25 degrees C. The reaction was not influenced by changing phosphate buffer concentration from 10 to 100 mM. The rate of reduction at the physiological pH, 7.0, was about 95% of the maximal value that observed at around pH 6.4. Formation of deoxyhemoglobin and oxidized form of flavin mononucleotide by the reaction proceeded stoichiometrically in a ratio of unity. These results apparently indicate that the limiting step for the reduction of methemoglobin by the NADPH-flavin reductase system in human erythrocytes is the enzymatic reduction of flavin.

Flavin Mononucleotide↗
PubMed1980

Enzymatic reduction of hemoglobins M Milwaukee-1 and M Saskatoon by NADH-cytochrome b5 reductase and NADPH-flavin reductase purified from human erythrocytes.

Enzymatic reduction of the hemoglobin (Hb) M group was studied. Hb M Milwaukee-1 and Hb M Saskatoon were reduced by NADH-cytochrome b5 reductase highly purified from human erythrocytes. Hb M Saskatoon was also reduced by another enzyme in red cells, NADPH-flavin reductase. The reduction rates of Hb M Saskatoon by both enzymes were almost the same as those of MetHb A. The reduction of Hb M Milwaukee-1 by NADH-cytochrome b5 reductase progressed much more slowly than that of Hb M Saskatoon and MetHb A. It took 1/2 h and 10 h for the 50% reduction of Hb M Saskatoon and Hb M Milwaukee-1, respectively. These two methemoglobin reductases from erythrocytes did not reduce other hemoglobins M such as Hb M Iwate, Hb M Boston, or Hb M Hyde Park. A possible role of these abnormal hemoglobins as oxygen carriers and the reason for cyanosis in the patients of Hb M Saskatoon and Hb M Milwaukee-1 are discussed.

Cytochrome Reductases↗
PubMed1980

Characterization of the purified NADH-cytochrome b5 reductase of human erythrocytes as a FAD-containing enzyme.

NADH-cytochrome b5 reductase of normal human erythrocytes was purified by procedures including affinity chromatography on Blue-Sepharose to an electrophoretically homogeneous protein. The purified enzyme was judged to be a typical flavoprotein based on its absorption spectrum (absorption maxima, 272, 390, and 462 nm; shoulders, 373 and 488 nm) and flavin content (1 mol of FAD/mol of enzyme). The minimum molecular weight calculated from the flavin content was 32,300. The purified enzyme showed a distinct negative circular dichroic spectrum at 280 nm and also at 460 to 480 nm. With the best preparations, the molar ellipticities at 280 and 460 nm were well correlated with the enzyme activity and flavin content in the enzyme. A partial loss of flavin from the enzyme led to a concomitant loss of enzyme activity and decrease in the molar ellipticities at 460 and 280 nm. Flavin analogues such as acrinol and proflavine (0.1 mM) strongly inhibited the enzyme activity, and atebrin (0.1 mM) also showed partial inhibition. Complete inhibition was observed with 1 mM of any these reagents. These results apparently indicate that FAD in the enzyme functions as a prosthetic group, and that circular dichroic spectroscopy is a good measure of the bound form of flavin in the enzyme.

Animals↗
PubMed1980

Reduction of methemoglobin through flavin at the physiological concentration by NADPH-flavin reductase of human erythrocytes.

The reduction of methemoglobin by NADPH-flavin reductase of human erythrocytes through flavin was studied under various conditions using a reconstituted methemoglobin reductase system. The reduction of methemoglobin by the reconstituted enzyme system could be easily detected with flavin at the physiological concentration (e.g., 0.1-1.0 microM), and the rates obtained with 0.1 and 1.0 microM FMN were 0.19 and 2.2 nmol heme reduced per min per ml, respectively, in the absence of oxygen. FMN was more effective than FAD in reduction by the reconstituted enzyme system, and oxygen decreased the rate of the reduction. The reduction of methemoglobin by the reconstituted enzyme system with flavin at a physiological concentration proceeded as a zero order reaction. These results apparently suggest that the NADPH-flavin reductase system is able to reduce methemoglobin in erythrocytes at a moderate speed with about 1 microM flavin, and the reduction was estimated to vary from less than 1% to about 20% of that by the NADH-cytochrome b5 reductase system with 1 microM cytochrome b5, depending on the uptake of flavin by human erythrocytes.

Cytochrome-B(5) Reductase↗
PubMed1979

Kinetic studies on methemoglobin reduction by human red cell NADH cytochrome b5 reductase.

The intermediate hemoglobins which were produced by the partial reduction of methemoglobin with human red cell NADH cytochrome b5 reductase were fractionated by the preparative isoelectric focusing. These were found to be composed of alpha3+beta2+ and alpha2+beta3+ valency hybrids by the studies of absorption spectra and inositol hexaphosphate-induced difference spectra. Furthermore, the changes in these intermediate hemoglobins during reduction of methemoglobin by the enzyme were studied in the presence or absence of inositol hexaphosphate using the isoelectric focusing fractionation on Ampholine plate gel...

Cytochrome Reductases↗
PubMed1979

Changes in intermediate haemoglobins during methaemoglobin reduction by NADPH-flavin reductase.

The changes in intermediate haemoglobins produced during methaemoglobin reduction by NADPH-flavin reductase were analysed by an isoelectric-focusing method. The alpha 3+ beta 2+ and alpha 2+ beta 3+ valency hybrids were observed as intermediate haemoglobins and changed consecutively with time during the reaction. On the basis of the analyses, the course of methaemoglobin reduction was found to involve two different pathways: (1) methaemoglobin kappa+1 leads to alpha 3+ beta 2+ kappa+2 leads to oxyhaemoglobin; (2) methaemoglobin kappa+3 leads to alpha 2+ beta 3+ kappa+4 leads to oxyhaemoglobin. The reaction rate constants of each phase (kappa+1--kappa+4) were also estimated. The addition of inositol hexaphosphate to the reaction mixture did not affect the overall reaction. The mechanism of methaemoglobin reduction by NADPH-flavin reductase is discussed on the basis of these results.

Cytochrome-B(5) Reductase↗
PubMed1978

Acceleration of methaemoglobin reduction by riboflavin in human erythrocytes.

The effect of riboflavin on nitrite treated erythrocytes from normal subjects and patients with hereditary methaemoglobinaemia due to the deficiency of NADH-cytochrome b5 reductase was studied in the presence of glucose, 2-deoxy-D-glucose or lactate. When glucose or 2-deoxy-D-glucose was used as a substrate for these erythrocytes, the rate of methaemoglobin reduction in these cells was accelerated more than two-fold in the presence of riboflavin. The acceleration was dependent on the concentration of riboflavin and was suppressed by the addition of atebrin. The stimulative effect of riboflavin was, however, not observed when lactate was used in place of glucose or 2-deoxy-D-glucose. On the basis of these results, the acceleration of methaemoglobin reduction by riboflavin was considered to be due to the activation of NADPH-flavin reductase (Yubisui et al, 1977) in erythrocytes by the reagent. The availability of riboflavin for patients with methaemoglobinaemia due to the deficiency of NADH-cytochrome b5 reductase and for those with toxic methaemoglobinaemia is discussed in relation to methaemoglobin reducing systems in erythrocytes.

Cytochrome-B(5) Reductase↗