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Y Ikegami

Publications and source records attributed to Y Ikegami.

90 records · Page 5Linked to original sources
PubMed1985

Different behavior towards raw starch of three forms of glucoamylase from a Rhizopus sp.

Three forms of glucoamylase [EC 3.2.1.3] of a Rhizopus sp., Gluc1 (M.W. 74,000), Gluc2 (M.W. 58,600), and Gluc3 (M.W. 61,400), which have similar pH optima and specific activities towards soluble starch were studied as to their behavior towards raw starch. The pH optima for raw starch digestion were different, that is, 4.5 for Gluc1 and 5.0 for both Gluc2 and Gluc3. All the enzymes digested raw starch almost completely but at quite different rates; Gluc2 and Gluc3, which lack the N-terminal portions of Gluc1, were 22 and 25 times less effective, respectively, for raw starch digestion than Gluc1. Of the three enzymes, only Gluc1 tightly bound to raw starch. Binding of Gluc1 to raw starch occurred pH-dependently with a broad pH optimum of 4.5-5.5, but temperature and ionic strength affected it only slightly and little, respectively. The binding constant of Gluc1 for raw starch at pH 5.0 and 4 degrees C was estimated to be 1.2 X 10(5) M-1. Fragment H (M.W. 16,700), presumably released from the N-terminal part of Gluc1, not only bound to raw starch itself but also inhibited the binding of Gluc1 to raw starch. pap-Gluc (M.W. 57,000) and chymo-Gluc (M.W. 64,000), which are papain- and chymotrypsin-modified Gluc1, respectively, and lack the N-terminal portions of Gluc1, resembled Gluc2 and Gluc3 in raw starch binding as well as digestion. All these results indicate that Gluc1 has a raw starch-binding site, different from the active center, in the N-terminal region. Various substrates and analogs inhibited the binding of Gluc1 to raw starch, presumably due to steric hindrance.

Glucan 1,4-alpha-Glucosidase↗
PubMed1985

DNA strand scission by enzymatically reduced mitomycin C: evidence for participation of the hydroxyl radical in the DNA damage.

Phage DNA, as well as plasmid and mammalian DNA's, were exposed to a superoxide and hydroxyl radical-generating system containing NADPH-cytochrome P-450 reductase and mitomycin C, both with and without added Fe3+-ADP, in phosphate buffer at pH 7.5. The generation of superoxide (O2-.) and hydroxyl (.OH) radicals in the system was demonstrated by using ESR spectrometry with N-tert -butyl-alpha-phenylnitrone (PBN) as a spin trapping agent. Only the lambda DNA isolated after exposure to the O2-./.OH-generating system containing many lower molecular weight DNA fragments indicating DNA strand breaks. This breakage was completely inhibited by a .OH radical scavenger (sodium benzoate) and by catalase, but only slightly by superoxide dismutase. Thyroid and plasmid DNA's were both cleaved when exposed to the O2-./.OH-generating systems. It is suggested that the mechanism of DNA scission by mitomycin C described here closely resembles that induced by the anthracycline drugs.

Animals↗
PubMed1984

Importance of Fe2+-ADP and the relative unimportance of OH in the mechanism of mitomycin C-induced lipid peroxidation.

The mechanism of mitomycin C-induced lipid peroxidation has been studied at pH 7.5, using systems containing phospholipid membranes (liposomes) and an Fe3+-ADP complex with purified NADPH-cytochrome P-450 reductase. Both O2- and H2O2 are generated during the aerobic enzyme-catalyzed reaction in the presence of mitomycin C. Hydroxyl radical is formed in the reaction by the reduction of H2O2. This is catalyzed by the Fe2+-ADP complex in a phosphate buffer or to a lesser extent when in a Tris-HCl buffer. The reduction of Fe3+-ADP to Fe2+-ADP is mainly achieved by O2-. The resulting Fe2+-ADP in the presence of O2 forms a perferryl ion complex which is a powerful stimulator of lipid peroxidation. However, the formation of such an iron-oxygen complex is strongly inhibited by phosphate ions, which do not interfere with the generation of OH radicals. These findings suggest that, since lipid peroxidation occurs in a Tris-HCl buffer (but not in a phosphate buffer), the OH radical is unlikely to be involved in the observed lipid peroxidation process.

Adenosine Diphosphate↗
PubMed1984

Dosage form design for improvement of bioavailability of levodopa VI: formulation of effervescent enteric-coated tablets.

A new dosage form of levodopa, which has the characteristics of loading high concentrations of levodopa at the upper part of the intestine, has been developed to improve its bioavailability. It is shown that an effervescent tablet formulation, coated with hydroxypropyl methylcellulose phthalate (carboxybenzoyl radical content: 20-24%) as the enteric material, is suitable for the purpose of dissolution. This was confirmed from animal experiments, which showed that tablets of this composition disintegrate instantly on reaching the upper part of the intestine. This tablet was considered appropriate for the bioavailability tests described in this paper.

Animals↗
PubMed1984

Clear evidence for the participation of OH in lambda DNA breakage induced by the enzymatic reduction of adriamycin in the presence of iron-ADP. Importance of local OH concentration for DNA strand cleavage.

lambda DNA (a double-stranded DNA) was exposed to several adriamycin-mediated active oxygen generating systems (O2- and H2O2 generating, OH generating, and perferryl ion complex generating), extracted, and analyzed by gel electrophoresis on agarose gel. Only the DNA exposed to and subsequently isolated from the adriamycin-mediated OH generating system contained many DNA fragments of low molecular weight, indicating the breakage of DNA strands. Such a breakage was strikingly inhibited by catalase or 50 mM sodium benzoate, but not by superoxide dismutase. The local OH concentration near the DNA strand was considered to be important for DNA strand cleavage.

Adenosine Diphosphate↗
PubMed1983

Generation of hydroxyl radicals during the enzymatic reductions of the Fe3+-ADP-phosphate-adriamycin and Fe3+-ADP-EDTA systems. Less involvement of hydroxyl radical and a great importance of proposed perferryl ion complexes in lipid peroxidation.

A system which contains NADPH, purified cytochrome P-450 reductase (enzyme) and Fe3+-ADP-adriamycin complex in Tris-HCl buffer does not produce hydroxyl radical, but possesses a strong lipid peroxidation activity on exogenously added phospholipid micelles. Fe3+-ADP-adriamycin complex, a tightly coordinated complex in Tris-HCl buffer, could be dissociated to Fe3+-ADP-phosphate complex and adriamycin in phosphate buffer. Hydroxyl radical, which can be detected by a spin trapping method using N-tert-butyl-alpha-phenylnitrone, is produced during the enzymatic reduction of a mixture of Fe3+-ADP-phosphate complex and adriamycin or of Fe3+-ADP-EDTA complex while it is not involved in phospholipid peroxidation under the conditions used. With hydroxyl radical-generating systems, little or no quenching of hydroxyl radical in Tris-HCl buffer could be demonstrated. The oxidative cleavage of phospholipid is initiated by the proposed perferryl ion complex, which may be generated by the interaction of Fe2+-ADP-adriamycin complex with O2. A similar perferryl ion complex is also produced during the enzymatic reduction of Fe3+-ADP-EDTA complex with a molar ratio of 2 for [Fe3+]/[EDTA] in the presence of air. This is also able to catalyze lipid peroxidation.

Adenosine Diphosphate↗
PubMed1979

Tennis: the effects of grip firmness on ball velocity after impact.

The effects of grip firmness on the ball velocity after impact has been investigated in tennis. The average horizontal velocity of the ball prior to contact and after completion of contact was determined by a motion-picture camera. A tennis ball was fired from a machine to impact with a tennis racket, which was fixed in several different positions. No significant difference was found between the velocity of the ball after impact with a racket which was horizontally clamped and with a racket in a balanced, upright position. The velocity ratio (post-impact vs pre-impact velocity) was an inverse function of the velocity of impact.

Hand↗
PubMedDate not supplied

Fluorescence digital image analysis of serotonin-induced calcium oscillations in single blood platelets.

The intracellular concentration of Ca2+ [( Ca2+]i) was monitored continuously in single rabbit blood platelets by digital imaging microscopy in conjunction with Fura-2, a specific Ca(2+)-indicator dye. Ionomycin as well as aluminium fluoride caused sustained increase in [Ca2+]i in the platelet, but oscillations of [Ca2+]i were not observed. Serotonin (5-HT) induced oscillatory increases in [Ca2+]i in the presence of 1 mM CaCl2; these had not been detectable in cell populations because the oscillations were not in synchrony. This effect of 5-HT was diminished when CaCl2 was omitted from the medium, and was antagonized by 1 microM ketanserin, a specific 5-HT2 receptor antagonist. Furthermore, DOI, a specific 5-HT2 agonist, had the same effect as 5-HT at lower concentration. A specific effector mechanism, not fully understood at present, therefore appears to mediate 5-HT2 receptors thereby allowing rabbit platelets to generate [Ca2+]i oscillations. It is suggested that protein kinase C in platelets might play a key role in the regulation of [Ca2+]i, and possibly in [Ca2+]i oscillations.

Aluminum↗