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N Shimamoto

Publications and source records attributed to N Shimamoto.

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

Identification and characterization of the direct folding process of hen egg-white lysozyme.

Refolding kinetics of hen egg-white lysozyme (HEWL) have been studied by means of the stopped-flow method with guanidinium chloride as the denaturant. We show here that the three-species model U1 in equilibrium or formed from U2 in equilibrium or formed from N (U1 and U2 = unfolded; N = native) now established for pancreatic ribonuclease A is also valid for HEWL on the basis of the following lines of evidence: (1) refolding kinetics outside the transition region are biphasic; (2) dependence of the fractional amplitude for the fast phase on the ratio of the time constants of the two phases agrees with theory; (3) unfolding kinetics outside the transition region are of single phase; (4) direct evidence for the U2 leads to U1 transformation is obtained by double-jump experiments; (5) the time constant of the binding reaction of a substrate analogue, 4-methylumbelliferyl N,-N'-diacetyl-beta-chitobioside, to HEWL molecules during refolding reaction agrees with the time constant of the direct refolding phase U2 leads to N. The characteristic properties of the nucleation-controlled reaction of refolding of small globular proteins are discussed in general. The results of the discussion are used to suggest that the direct folding process is nucleation controlled from the experimental results of the temperature dependence of the refolding rate.

Dose-Response Relationship, Drug↗
PubMed1982

Coronary circulatory failure and thromboxane A2 release during coronary occlusion and reperfusion in anaesthetised dogs.

Attempts were made to demonstrate release of vasoactive substances from the heart during coronary occlusion (for 60 min) and reperfusion (for 60 min), and to clarify the pathophysiological significance of them. Vasoactive substances were detected by superfusion of rabbit aortic and dog coronary arterial strips with great coronary venous blood. Plasma thromboxane (TX) B2 was radioimmunologically assayed. Gradually developing, sustained contraction of both vascular strips was noted during coronary occlusion and reperfusion, while a transient contraction in rabbit aortic and relaxation in dog coronary arterial strips were seen immediately after reperfusion. The TXB2 released into the great coronary venous blood significantly increased during occlusion and reperfusion. Indomethacin treatment of the dog abolished the sustained contraction of both vascular strips and TXB2 release. The transient contraction of rabbit aorta after reperfusion was inhibited by phenoxybenzamine. Reactive hyperaemia following a 60 min occlusion was significantly depressed, as compared with that following 30 s to 30 min occlusion, and the depression was alleviated by indomethacin and imidazole. These results suggest that catecholamine(s) and TXA2 are released during coronary occlusion and reperfusion, and that the latter might be responsible for the coronary circulatory failure during reperfusion of irreversibly damaged myocardium.

Animals↗
PubMed1982

Absence of DNA in peroxisomes of Candida tropicalis.

Yeast peroxisomes were purified to near homogeneity from cells of Candida tropicalis grown on oleic acid for the purpose of examining the possible presence of DNA in this organelle. The purification procedure includes the effective conversion of cells to spheroplasts with Zymolyase and sodium sulfite and the separation of the organelles at extremely low ionic strength. The mitochondrial contamination was less than 1%, based on several criteria, and the yield of peroxisomes was about 40%. The purified peroxisomal fraction contained a very small amount of DNA, which yielded restriction fragments indistinguishable from those of mitochondrial DNA. The absence of DNA in peroxisomes was also supported by cesium chloride density gradient centrifugation of the organelles lysed with a detergent, staining of the organelles with a fluorescent dye specific to DNA, and labeling of the DNA with [3H]adenine.

Adenine↗
PubMed1982

[Effects of 2,3-dimethoxy-5-methyl-6-(10'-hydroxydecyl)-1,4-benzoquinone (CV-2619) on myocardial energy metabolism in the hypertrophied heart of spontaneously hypertensive rats].

Effects of CV-2619 (10 and 30 mg/kg/day, p.o.) or ubiquinone-10 (Q-10, 10 mg/kg/day, p.o.) treatment for 5 weeks on systolic blood pressure (SBP) and myocardial energy metabolism were studied in spontaneously hypertensive rats of 20 weeks of age. The systolic blood pressure was about 205 mmHg at the start of the experiment, and a slight increase was noted thereafter in the control (vehicle) group. CV-2619, but not Q-10, inhibited the increase in the blood pressure. At 25 weeks of age, cardiac hypertrophy was noted to the same extent in either treated group. Myocardial contents of glycolytic intermediates (glycogen, glucose, pyruvate and lactate) and creatine phosphate (Cr-P), ATP, ADP, and AMP were not significantly influenced by CV-2619 or Q-10 treatment. CV-2619, however, significantly increased the energy charge, an index of myocardial energy state, with higher dose and lowered the lactate/pyruvate ratio with either dose. These results suggest that CV-2619 has a mild antihypertensive effect and improves the myocardial energy state in the hypertrophied heart during the sustained phase of hypertension in SHR rats.

Animals↗
PubMed1982

[Effects of 2,3-dimethoxy-5-methyl-6-(10'-hydroxydecyl)-1,4-benzoquinone (CV-2619) on adriamycin-induced ECG abnormalities and myocardial energy metabolism in spontaneously hypertensive rats].

Antidote actions of CV-2619 and ubiquinone-10 (Q-10) against adriamycin (ADM) cardiotoxicity were studied in spontaneously hypertensive rats. ADM (1 mg/kg/day, i.p.) elicited widening of the QRS complex in the ECG. The widening of the QRS complex was counteracted by a 10-day treatment with CV-2619 (10 and 30 mg/kg/day, p.o.) or Q-10 (10 mg/kg/day, p.o.), which was started on the 15th day of the ADM treatment. CV-2619 or Q-10, however, did not influence ADM-induced decrease in body and heart ventricular weights. Systemic hypotension caused by adriamycin was accelerated by CV-2619 or Q-10. The ADM treatment significantly decreased myocardial glycogen and glucose contents, while it did not affect the lactate content. Furthermore, ADM did not affect the myocardial content of adenine nucleotides, but significantly increased that of creatine phosphate. CV-2619 or Q-10 medication did not counteract changes in these contents by ADM. On the contrary, both agents decreased the lactate content and increased the phosphorylation potential, an index of myocardial energy state. In conclusion, CV-2619 might be as effective as Q-10 to protect the heart against ADM cardiotoxicity, and both test agents improved the myocardial energy state.

Animals↗
PubMed1982

[Effects of 2,3-dimethoxy-5-methyl-6-(10'-hydroxydecyl)-1,4-benzoquinone (CV-2619) on the energy metabolism of red blood cells of rats].

Effects of CV-2619 and ubiquinone-10 (Q-10) on the energy metabolism of red blood cells (RBC) of Sprague Dawley rats were studied in the presence or absence of NaF. NaF (0.3--10 mM) dose-dependently decreased the ATP and lactate contents of the RBC. In the presence of NaF (1.5 mM), ATP content decreased to about 30% of the control. Phosphofructokinase (PFK) was markedly activated, while glyceraldehydephosphate dehydrogenase (GAPDH) and enolase were inhibited by NaF. Thus, the decrease in ATP by NaF might be attributed to retarded glycolysis due to inhibition of the latter two enzymes. The decrease in ATP by NaF (1.5 mM) was dose-dependently inhibited by CV-2619 (0.3--30 microM). Inhibition of enolase and activation of PFK by NaF were still noted even in the presence of CV-2619. Inhibition of GAPDH by NaF, however, was released by CV-2619. Q-10 (1--100 microM) did not affect the ATP levels decreased by NaF. It could be concluded that CV-2619 counteracted the NaF-induced decrease in the ATP level by accelerating the glycolytic flux through the GAPDH step, which was a rate-limiting one in the presence of NaF. Q-10, however, had no effect on the glycolytic flux.

Adenosine Triphosphate↗
PubMed1981

Spectral evidence for a rapidly formed structural intermediate in the refolding kinetics of hen egg-white lysozyme.

For investigation of the conformation of the unfolded species and its role in the refolding kinetics, refolding kinetic measurements were made on hen egg-white lysozyme by using the stopped-flow method at 25 degrees C in the four sets of initial and final folding condition: (1) 4 M guanidinium chloride (GdmCl) and 0.5 M GdmCl; (2) 40% acetic acid (HOAc) and 5% HOAc; (3) 4 M GdmCl and 0.5 M GdmCl-5% HOAc; (4) 40% HOAc and 0.5 M GdmCl-5% HOAc. The kinetic results as measured by absorbance at three wavelengths, 301, 292, 250 nm, agreed with each other and indicated strict biphasic behavior without exception. The kinetic parameters were determined only by the final refolding conditions. The spectral properties of the unfolded species at the end of stopped-flow mixing were investigated by comparing the total kinetic amplitude with the difference between the static absorbance of the native molecule in the final refolding conditions and that of the unfolded molecule in the initial unfolding conditions. The solvent effect was considered in the comparison. It was concluded that the unfolded species assumed a new transient conformation in the mixing process and that the transformation was completed within the mixing time.

Egg White↗
PubMed1980

Mechanism of ribonucleic acid chain initiation. 1. A non-steady-state study of ribonucleic acid synthesis without enzyme turnover.

A non-steady-state kinetic method has been developed to observe the initiation of long RNA chains by Escherichia coli RNA polymerase without the enzyme turnover. This method was used to determine the order of binding of the first two nucleotides to the enzyme in RNA synthesis with the first two nucleotides to the enzyme in RNA synthesis with poly(dA-dT) as the template. It was shown that initiator [ATP, uridyly(3'-5')adenosine, or adenyly(3'-5')uridylyl-(3'-5')adenosine] binds first to the enzyme-template complex, followed by UTP binding. The concentration dependence of UTP incorporation into the initiation complex suggests that more than one UTP molecule may bind to the enzyme-DNA complex during the initiation process. Comparison of the kinetic parameters derived from these studies with those obtained under steady-state conditions indicates that the steps involving binding of initiator or UTP during initiation cannot be rate limiting in the poly(dA-dT)-directed RNA synthesis. The non-steady-state technique also provides a method for active-site titration of RNA polymerase. The results show that only 36 +/- 9% of the enzyme molecules are active in a RNA polymerase preparation of high purity and specific activity. In addition, the minimal length of poly(dA-dT) involved in RNA synthesis by one RNA polymerase molecule was estimated to be approximately 500 base pairs.

DNA-Directed RNA Polymerases↗
PubMed1980

Pathophysiological significance of coronary collaterals for preservation of the myocardium during coronary occlusion and reperfusion in anaesthetised dogs.

The significance of pre-existing coronary collaterals for preservation of the myocardium during coronary occlusion and reperfusion was studied in anaesthetised open-chest dogs. The extent of myocardial ischaemic damage was assessed by the accumulation of calcium in the central zone of the ischaemic area and the size of myocardial infarct by the p-nitroblue tetrazolium staining method. Myocardial creatine kinase release was considered as an index reflecting both the extent of ischaemic myocardial damage and the size of the infarct. Reperfusion with the arterial blood of a main branch of the left coronary artery following the 60 min occlusion aggravated the ischaemic myocardial damage, as evidenced by exaggerated cardiac irregularity, myocardial calcium accumulation, and creatine kinase release. The myocardial calcium content and the logarithm of the creatine kinase release during reperfusion were linearly related to the infarct size. These parameters of myocardial damage were inversely related to the retrograde blood flow through the peripheral end of the occluded artery or the ratio of the retrograde-to-orthograde flow, indicating that the pre-existing collaterals influence preservation of the ischaemic myocardium. Thus, it is suggested that the collateral flow available during an ischaemic episode determines the viability of the myocardial cells during ischaemia, and in turn during reperfusion.

Animals↗
PubMed1980

[Using the isolated atrial preparation of the guinea-pig and the canine heart lung preparation (HLP) supported by a donor, the effects of guanfacine on the heart, coronary circulation and myocardial energy metabolism were studied and compared with those of clonidine (author's transl)].

In the isolated left atria of the guinea-pig, guanfacine and clonidine (10(-8)--3 x 10(-5) g/ml) produced positive inotropic effects, which were inhibited by tripelennamine, metiamide and propranolol. Up to the concentration of 10(-6) g/ml of these compounds the effects were also inhibited by phentolamine. In the isolated right atria, guanfacine in concentrations over 3 x 10(-6) g/ml, produced a negative, and clonidine, a positive chronotropic effect. Whereas the effect of clonidine was antagonized by metiamide, the effect of guanfacine was not antagonized by any blocking agents we used. In spontaneously beating right atria, the positive inotropic effects induced by guanfacine (10(-8)--10(-5) g/ml) were inhibited by propranolol or tripelennamine, while those of clonidine (10(-8)--10(-4) g/ml) were antagonized by metiamide. In canine HLP, both drugs produced a decrease in the coronary flow which was associated with a slight rise in the right atrial pressure. These effects were inhibited by phentolamine. Both drugs produced a slight decrease in the myocardial O2 consumption and an improvement of the myocardial redox potential.

Animals↗