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Biomedical subjects

M Okamoto

Publications and source records attributed to M Okamoto.

At least 1,009 records · Page 56Linked to original sources
PubMed1984

Integrated function of a kinetic proofreading mechanism: dynamic analysis separating the effects of speed and substrate competition on accuracy.

All of the data relating to isoleucyl-tRNA synthetase and its proofreading of valyl-tRNAIle have been integrated into a single model whose dynamic behavior has been determined by numerical solution of the relevant kinetic equations. The results indicate that (1) the system normally operates in vivo with amino acid concentrations slightly above the apparent Km of the system, (2) increases in the displacement of reactants from thermodynamic equilibrium increase the net reaction velocity when the appropriate nominal parameter values are selected, (3) the cost of proofreading decreases with an increase in displacement of reactants from equilibrium, (4) accuracy and reaction velocity tend to be inversely related when substrate competition is unchanged but directly related or unrelated when substrate competition is altered, (5) changes in substrate competition are about twice as effective as changes in reaction velocity in altering the overall accuracy of aminoacylation, and (6) simultaneous changes in substrate competition and reaction velocity have a cumulative but not additive effect upon accuracy. With regard to the temporal development of errors and proofreading costs, we have seen two different patterns. In one, errors or costs gradually change with time following an abrupt alteration; in the other, errors or costs change dramatically in one direction and then more slowly reverse themselves. In all cases, the system responds to change quickly (less than 0.02-0.2 s) but shows no tendency to oscillate.

Amino Acyl-tRNA Synthetases↗
PubMed1984

Polymorphic transition of the flagellar polyhook from Escherichia coli and Salmonella typhimurium.

Bacterial flagellar polyhook fibers were reversibly transformed into a set of helical forms depending on pH, ionic strength and temperature. Electron microscopy with formalin fixation and freeze-drying was useful for observing three-dimensional shapes of various polyhook helices and determining their helical handedness. A Cartesian plot of curvature against twist for these polyhook helices gave a sinusoidal curve as in the case of the polymorphic forms of flagellar filament. In the study on the polymorphism of flagellar filaments. Calladine (1976, 1978) and Kamiya et al. (1979) pointed out that such a relation in the polymorphic forms could be derived from the assumption that the subunits on the near-longitudinal (11-start) helical lines should work as elastic fibers (protofilaments) having two distinct states of conformation. In contrast, the observed twist for the polyhook helices is too large to be explained by the same assumption. Instead, we must assume that subunits on the strongly twisted, 16-start helical line should work as the co-operative protofilament.

Elasticity↗
PubMed1984

Aldosterone biosynthesis by a reconstituted cytochrome P-45011 beta system.

[3H]Corticosterone was incubated with cytochrome P-45011 beta purified to electrophoretic homogeneity from bovine adrenocortical mitochondria, and the reaction products were analyzed by high performance liquid chromatography. The production of aldosterone (21.2 pmol/nmol P-450/min) and 18-hydroxycorticosterone (1.17 nmol/nmol P-450/min) was observed. When lipidic extracts from mitochondria of bovine adrenocortical zona glomerulosa were added to the reaction mixture, the rate of production of aldosterone was increased 28-fold. When [3H]18-hydroxycorticosterone was incubated with cytochrome P-45011 beta, the amount of aldosterone produced was 55.7 pmol/nmol P-450/min in the absence of the lipidic extracts and the enhancing effect of the lipidic extracts was 4-fold.

18-Hydroxycorticosterone↗
PubMed1984

Augmentation of atrial contribution to left ventricular inflow with aging as assessed by intracardiac Doppler flowmetry.

The influence of aging on the left ventricular (LV) function in diastole was investigated from the aspect of the mitral inflow pattern using 2-dimensional Doppler echocardiography. The subjects for the investigation were 69 persons who were diagnosed as healthy by a checkup examination. The peak velocity in the rapid filling phase and that in the atrial contraction phase tended to decrease and to increase with aging, respectively. However, these tendencies were not statistically significant. However, the ratio of the atrial contraction phase to the rapid filling phase showed a significant increase with aging (r = 0.82, p less than 0.001). Therefore, it is considered that the mitral flow conditions are influenced by aging. The result obtained is also interpreted to mean that the LV distensibility in early diastole is impaired with aging and that the contribution of the atrial contraction to LV filling is compensatorily augmented.

Adult↗
PubMed1984

Purification of intracellular phospholipase A2 from rat spleen supernatant by reverse-phase high-performance liquid chromatography.

Intracellular phospholipase A2 was purified to homogeneity from rat spleen supernatant by reverse-phase high-performance liquid chromatography with a trifluoroacetic acid-acetonitrile solvent system. The method simplified the purification procedure, which includes three consecutive chromatographic steps. The recovery of the enzyme activity was greater than 70% with an about 23,000-fold purification. The solvent system did not affect the catalytic properties of the enzyme. Phospholipases A2 from rat spleen, human pancreatic juice, and porcine pancreas were eluted in that order from a column of octadecasilyl silica gel in a similar concentration range of acetonitrile. This result suggests that the phospholipases A2 examined have similar hydrophobicities. This method may be applicable to the purification of phospholipases A2 from other sources.

Animals↗
PubMed1984

Structural change of myofibrils during mitosis of newt embryonic myocardial cells in culture.

Newt embryonic myocardial cells can undergo mitosis in culture. The successive changes in the striation pattern of sarcomeres of myofibrils during mitosis were studied by polarization microscopy without fixing or killing the cells. Birefringence of well-organized striation patterns, i.e., bright A-bands and dark I-bands, was clearly visible in interphase cells and did not show any detectable changes during incubation for 3 h or more. Electron microscopy showed the presence of well-organized myofibrils with Z-bands in these interphase cells. When myocardial cells entered the mitotic stage, the birefringence of striation pattern of their myofibrils gradually changed with the pattern in small parts of the myofibrils gradually becoming indistinct (called 'indistinct striation' in this paper). These indistinct regions increased in size during the mitotic stage. In addition, in some regions of the indistinct striation, the birefringence of sarcomeres gradually decreased and finally disappeared (called 'disappearance of sarcomeres' in this paper). No myocardial cells underwent mitosis without these disruptive changes of the myofibril striation patterns. In the post-mitotic stage, the well-organized striation of the myofibrils reappeared. Electron microscopy showed disorganized sarcomeres without Z-bands in the regions of indistinct striation, and no well-organized myofibrils in the regions where the sarcomeres had disappeared. Thus the well-organized myofibrils with Z-bands became transiently disorganized at least in some parts, during mitosis. They were then reorganized into daughter myocardial cells.

Animals↗
PubMed1984

Cortical and subcortical EEG patterns during moderate-intensity barbiturate withdrawal.

Electroencephalograms were recorded from cortical and subcortical brain regions during moderate-intensity barbiturate withdrawal in the cat. Physical dependence was produced by administration of Na-barbital by the "low dose barbiturate" treatment schedule. During moderate-intensity withdrawal, the EEG pattern showed 4- to 6-Hz rhythmic bursts in the hippocampus, visual cortex, auditory cortex, motor cortex, nucleus centralis centralis of the thalamus, caudate nucleus, and lateral geniculate body. The bursts in the hippocampus were spike-and-wave type. In animals which had spontaneous seizures, 4- to 6-Hz bursts occurred in the motor cortex, whereas this abnormality did not occur in the motor cortex in animals which did not have spontaneous generalized seizures. In addition, prolonged high-frequency, high-voltage discharges and spikes were recorded from the amygdala during withdrawal. Spontaneous generalized or partial seizures occurred during withdrawal; the abnormal EEG patterns associated with seizures appeared to originate in various subcortical sites. Perhaps the most important result was the finding that no one brain region or set of brain regions seemed to be specifically involved in barbiturate withdrawal.

Animals↗
PubMed1984

Experience with the routine use of an abbreviated crossmatch.

Three years' experience with the routine use of an abbreviated crossmatch procedure is reported. If a patient had no known history of and/or no currently demonstrable unexpected antibodies, ABO and Rh type specific blood was crossmatched at the time of need by using an immediate spin saline abbreviated crossmatch. Once blood was issued, both a 37 degrees C incubation and an antiglobulin crossmatch were done using the same tube employed for the abbreviated crossmatch. This served as a check that clinically significant antibodies were not overlooked. None of the 19,818 patients transfused following an abbreviated crossmatch suffered an acute hemolytic transfusion reaction as a result of this strategy; however, two patients may have manifested asymptomatic hemolysis. This approach to compatibility testing might be appealing to hospitals faced with fiscal limitations and new regulations affecting hospital reimbursement.

Adult↗
PubMed1984

Rat pancreatic phospholipase A2: purification, characterization, and N-terminal amino acid sequence.

Phospholipase A2 was purified from rat pancreas by heat treatment of the homogenate and the sequential use of DEAE-Sepharose chromatography, CM-Sepharose chromatography, and reverse-phase high-performance liquid chromatography (HPLC). Prophospholipase A2 was not separated from the phospholipase A2 by CM-Sepharose chromatography under the conditions used, but it was well resolved by the reverse-phase HPLC. The enzyme was homogeneous on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and on analytical HPLC, and its molecular weight was estimated to be 14,000. The enzyme specifically hydrolyzed an acylester bond at the sn-2-position of the phospholipid examined. The purified enzyme has a pH optimum in the range of pH 9.5 to 10.5 and requires the presence of Ca2+ (3 mM) and sodium deoxycholate (0.1%) for optimum activity. The amino acid sequence of the first 32 residues in the N-terminal region of the enzyme was determined. The sequence revealed a marked homology with those of pancreatic phospholipases A2 of man, pig, ox, and horse, and porcine intestinal phospholipase A2 reported previously.

Amino Acid Sequence↗
PubMed1984

Sleep patterns in cats during chronic low-dose barbiturate treatment and withdrawal.

Sleep patterns were recorded during 5 weeks of chronic treatment with sodium barbital and after abrupt cessation of drug administration. Sodium barbital was administered intragastrically to adult cats twice daily in doses to produce a peak response of gross ataxia ("low-dose" barbiturate treatment). Sleep stages were scored from EEG, EOG, and neck EMG recordings from chronically implanted electrodes. Sleep was monitored continuously for 48 h once each week during barbital administration and continuously for 7 to 10 days during withdrawal. Rapid eye movement (REM) sleep during barbital treatment was reduced to approximately half compared with control. At the end of the treatment, equivalent doses of pentobarbital were substituted for barbital. Cessation of pentobarbital administration produced withdrawal. Withdrawal intensity was moderate and spontaneous convulsions occurred in half the animals. The duration of withdrawal insomnia was 2 to 3 days. Return of the non-REM and REM sleep was associated with changes in withdrawal behaviors, notably the appearance of overly affectionate behavior. Furthermore, during return of sleep both non-REM and REM sleep increased to values greater than control.

Animals↗
PubMed1984

Analysis of blood flow in pulmonary hypertension with the pulsed Doppler flowmeter combined with cross sectional echocardiography.

Blood flow patterns were analysed at nine points in the pulmonary area using the pulsed Doppler technique combined with cross-sectional echocardiography in 53 patients with heart disease and 10 healthy subjects. In subjects with a normal pulmonary artery pressure the blood flow pattern in systole showed a gradual acceleration and deceleration with a rounded summit in mid systole, designated the round type. In patients with pulmonary hypertension it showed a rapid acceleration and early deceleration with a sharp peak in early systole, designated the triangular type. The acceleration time index, defined as the ratio of the time interval from the beginning to the peak of ejection to the ejection time, showed a significant inverse correlation with mean pulmonary artery pressure. In pulmonary hypertension a prominent reverse flow occurred in the right posterior part of the pulmonary trunk during mid-systole and early diastole, indicating the presence of a vortex. Similar flow patterns were also seen in patients with idiopathic pulmonary artery dilatation. The factors responsible for the triangular type were principally the reduced capacitance and increased impedance of the pulmonary vascular tree. Those responsible for the reverse flow were the curved path of the blood flow and dilatation of the pulmonary artery.

Adult↗
PubMed1984

Doppler echocardiographic features of coronary arteriovenous fistula. Complementary roles of cross sectional echocardiography and the Doppler technique.

The Doppler echocardiographic features of coronary arteriovenous fistula were investigated in eight patients with left or right coronary arteriovenous fistulas who had a continuous heart murmur in the upper precordial area and whose diagnoses were confirmed by coronary angiography. In four patients the dilated lumen of the coronary arteriovenous fistula was visualised by cross sectional echocardiography. Of these, three showed abnormal unidirectional continuous flow signals with broad velocity spectra in the fistula. Abnormal, powerful, unidirectional or bidirectional continuous Doppler signals were detected in part of the pulmonary artery in two of the eight patients, in part of the right ventricle in two, and in part of the right atrium in one; these signals were interpreted as indicating shunt flow. Although the opening of the fistula was difficult to visualise by cross sectional echocardiography, the pulsed Doppler technique helped identify the site in patients with dilatation of the coronary artery. In the remaining three patients with a small shunt no abnormal findings were obtained with cross sectional echocardiography or the Doppler technique. The size of the fistula below which no abnormal findings may be obtained by Doppler echocardiography still needs to be determined.

Adult↗
PubMed1984

Homeostatic capability of rate-sensitive feedback system: mathematical model.

We have predicted the mathematical model of rate-sensitive feedback control system and have investigated its homeostatic capability by using computer simulations. The results are summarized as follows. By installing a cyclic enzyme system as feedback control element, we could assume the rate-sensitive feedback system at molecular level. This type of feedback had realistic constant-value control capability for external perturbations. This feedback system was more effective for the exclusion of perturbation than was the concentration-sensitive feedback. A large-loop feedback was more stable for perturbation than was short-loop feedback. In sequential feedback system, every key enzyme sensitive to feedback control had to vary the activity at same time for the system to keep homeostasis.

Animals↗
PubMed1984

Cytochrome P-450-dependent oxidative cleavage of 1-(tetrahydro-2-furanyl)-5-fluorouracil to 5-fluorouracil.

Cytochrome P-450-dependent oxidative cleavage of 1-(tetrahydro-2-furanyl)-5-fluorouracil (FT) was investigated in a reconstituted system containing purified phenobarbital-inducible cytochrome P-450 (P-450(1)) or 3-methylcholanthrene-inducible cytochrome P-450 (P-448(1)). FT was converted into 5-fluorouracil (5-FU) in the reconstituted system, and its rate was 71 pmol 5-FU formed/min/nmol P-4501 and 45 pmol 5-FU/min/nmol P-448(1). Cytochrome P-450, NADPH-cytochrome P-450 reductase and NADPH were required for 5-FU production. Inhibitors of cytochrome P-450 such as carbon monoxide and metyrapone markedly decreased the rate. FT was found to interact with the purified cytochrome P-450, causing a reverse type I spectral change. From these observations, we concluded that the hepatic microsomal cytochrome P-450-dependent mixed function oxidase system participates in the oxidative cleavage of FT.

Animals↗