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Biomedical subjects

K Shinohara

Publications and source records attributed to K Shinohara.

At least 343 records · Page 19Linked to original sources
PubMed1981

Enhancement of adenosine triphosphatase activity of purified chloroplast coupling factor 1 in aqueous organic solvent.

The ATPase activity of purified coupling factor 1 (CF1) of spinach chloroplasts [EC 3.6.1.3] was reversibly enhanced in some aqueous organic solvents, notably methanol, ethanol, and acetone. Pretreatment of CF1 with 20% (v/v) methanol did not affect the subsequent activity. The activity depended entirely on the final concentration of methanol in the reaction mixture. In the presence of 20% methanol, the Km of Ca2+-ATPase from ATP was lowered from 0.4 mM to 0.2 mM. Not only Ca2+, but also Cd2+, Mg2+, Mn2+, and Zn2+ supported the ATPase activity at rates of higher than 7 mumol.mg protein-1 . min-1. Co2+, Ni2+, and Pb2+ supported the activity at rates of 0.5-1.0 mumol.mg protein-1 . min-1. The activities supported by the following cations, if any, were less than 0.2 mumol.mg protein-1 . min-1; Ba2+, Cu2+, Fe2+, Hg2+, Sn2+, and Sr2+. The optimum concentration of methanol for Ca2+-ATPase and Mg2+-ATPase activities was about 30% (v/v). The optimum pH values for Ca2+-ATPase and Mg2+-ATPase activities were about 8.0 and 8.8, respectively. The enhancing effect of organic solvents appears to be associated with their relative lipophilic character as defined by the octanol-water partition coefficient. The Ca2+-ATPase activities of th trypsin-activated and the heat-activated CF1 were inhibited and their Mg2+-ATPase activities were enhanced by the presence of methanol in the reaction mixture.

Adenosine Triphosphatases↗
PubMed1980

Pyruvate kinase deficiency hemolytic anemia: enzymatic characterization studies in twelve patients.

Erythrocyte pyruvate kinase from twelve patients with hereditary erythrocyte pyruvate kinase (PK) deficiency was investigated according to the recommended methods for the characterization of red cell pyruvate kinase variants. Family members were also studied. Abnormalities were frequently noted in the affinity for the substrate, phosphoenolpyruvate; allosteric activator, fructose-1,6-diphosphate; allosteric inhibitor, ATP; and also in heat stability and electrophoretic pattern. Several different PK variants were identified. Polyacrylamide gel electrophoresis revealed the presence of immature activity bands in the red cells of some patients. These bands presumably represent residuals of isozymes produced during the evolution of erythrocyte PK, and may occur as a compensatory mechanism for the defective isozyme.

Adenosine Triphosphate↗
PubMed1980

The effects of adriamycin (doxorubicin HCl) on human red blood cells.

We have studied the effects of adriamycin (doxorubicin HCl) on human red blood cells. The peroxidizing effect of adriamycin on the thiols of red cell constituents resulted in decreased glutathione stability, and oxidation of hemoglobin and membrane protein components 1, 2, and 3, forming large molecular weight complexes. Membrane lipids were also peroxidized. Adriamycin itself did not inhibit the enzymes of the reductions system (glucose-6-phosphate dehydrogenase, 6-phosphogluconic dehydrogenase, glutathione reductase, glutathione peroxidase, catalase, superoxide dismutase) of the red cells. Because adriamycin has the potential of inhibiting ATPase, including both Na-K-dependent ATPase and ouabain insensitive ATPase, at concentrations not inhibitory to other enzymes, the net sodium content increased, and potassium content decreased after incubation of red cells with adriamycin at high concentrations. The experimental results described with adriamycin may serve as a model for the possible mechanism of cardiotoxicity observed in its clinical use, and also explain the potential hemolyzing effect on red cells. There was greater oxidizing effect on glucose-6-phosphate dehydrogenase (G-6-PD) deficient than on normal erythrocytes. It is suggested that adriamycin be used with caution in individuals with G-6-PD deficient red cells.

Adenosine Triphosphatases↗
PubMed1979

Kinetic and electrophoretic studies of human erythrocytes deficient in pyrimidine 5'-nucleotidase.

The mutant enzyme of a patient with hereditary pyrimidine 5'-nucleotidase deficiency was analyzed biochemically. Partially purified by DEAE-Sephadex and concentrated by ultrafiltration, the enzyme had a high Km for the substrate uridine monophosphate. Utilization of the substrate cytidine monophosphate was normal, but utilization of adenosine monophosphate was greatly increased. The enzyme was stable to heat; the pH optimum was acidic. Electrophoresis of the enzyme revealed a very faint, slower than normal band.

Adult↗
PubMed1979

Mechanism of inhibition of red blood cell glutathione reductase activity by BCNU (1,3-bis(2-chloroethyl)-1-nitrosourea).

A study of the mechanism of inhibition of glutathione reductase activity by BCNU (1,3-bis(2-chloroethyl)-1-nitrosourea) demonstrated that the enzyme was protected from inhibition by mercaptoethanol. N-Ethylmaleimide competes with BCNU and also protects the enzyme from inhibition. The inhibited enzyme showed decreased affinity for NADPH. Our data suggest that the inhibition of glutathione reductase is due to an alteration of the redox state. Several other red cell enzymes were inhibited by high concentrations of BCNU; these enzymes were also protected by mercaptoethanol. Among alkylating agents tested, only BCNU inhibited glutathione reductase at therapeutic levels.

Carmustine↗
PubMed1979

Hereditary deficiency of erythrocyte acetylcholinesterase.

A 36-year-old white man was found to have low erythrocyte acetylcholinesterase activity. Plasma cholinesterase activity was normal. The propositus had mild anemia and moderate elliptocytosis, but was asymptomatic. A sister, brother, father, and nephew were hematologically normal, but had slightly subnormal red cell acetylcholinesterase activities. There was no exposure to organophosphates, and paroxysmal nocturnal hemoglobinuria was excluded. Mixing experiments failed to demonstrate the absence of an activator or the presence of an inhibitor. The propositus enzyme showed normal kinetics for the substrate and various inhibitors, normal thermostability, and electophoretic migration. Major protein bands of the red cell membrane were normal by electrophoresis. Membrane cholesterol and phospholipid content were also normal. The mild anemia is presumably secondary to the presence of moderate elliptocytosis. The pattern of inheritance of the variant gene is unclear, but the propositus may be homozygous for the abnormal allele, and other family members may be heterozygous.

Acetylcholinesterase↗
PubMed1979

Hypothalamic thermo-responsive neurones in the new-born rat.

1. Single unit activities were recorded from the neurones in the preoptic area and anterior hypothalamus of developing new-born rats (aged 1-24 days old) during thermal stimulation of the brain. During the first 2 weeks of life, about 80% of these neurones had low spontaneous firing rates between 0.1 and 5 impulses/sec at 38 degrees C hypothalamic temperature (Thyp). 2. Out of 640 units studied, 118 units increased the firing rate upon elevation of Thyp (warm-units) and fourteen showed the opposite type of response to temperature changes (cold-units). Warm-units were found in the rats of all the age span studied and cold-units were recorded in the rats more than 8 days old. 3. Thermal coefficients of warm-units and cold-units varied between +0.11 and +2.47 and between -0.10 and -0.49 impulses/sec, degrees C, respectively. Number of warm-units with higher rates of firing and greater thermal coefficients, comparable to those of warm-units in the adult, gradually increased with growth. The thermal responsiveness of warm-units, when expressed by Q10, are already high even in the immediate neonatal period. Their Q10 values were in the range between 2 and 38.5 (mean 6.4). 4. Units responding to extrahypothalamic temperatures were only found in the rats more than 14 days old. 5. All the six warm-units tested increased the firing rates following subcutaneous injections of capsaicin, while the majority of thermo-unresponsive units were not affected by this drug. 6. It is suggested that thermo-responsive neurones in the preoptic area and anterior hypothalamus in the new-born rat have attained some degree of electrophysiological maturity, despite their slowly firing characteristics.

Action Potentials↗
PubMed1978

Breaking action of reductones related to ascorbic acid on nucleic acids.

The action of two types of ascorbate-related reductones on nucleic acids was investigated by comparison with that of ascorbic acid (AsA). Amino reductone (ScA) and thiol reductone (MHC) caused strandscissions in nucleic acids. This was confirmed by the fact that reductones lowered the viscosity of DNA solution and shifted the peaks of DNA and RNA to the low molecular side in centrifugal profile. Cu2+ strengthened their action as in the case of enediol reductones. The braking activity of thiol reductone is relatively wesk compared with those of amino and enediol reductones. The preferential degradation of spurinic acid was caused with amino and thiol reductones, suggesting that pyrimidine clusters in nucleic acids were susceptible to breakage.

4-Hydroxycoumarins↗