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Biomedical subjects

S Mitaku

Publications and source records attributed to S Mitaku.

At least 55 records · Page 3Linked to original sources
PubMed1993

Theoretical analysis of amino acid sequence of human dystrophin.

Human muscular dystrophy, the fatal disease, is caused by the genetic abnormality of dystrophin. The question whether dystrophin is an intrinsic membrane protein or not was investigated by calculating the average value and the long periodicity of hydrophobicity of amino acid sequence. The periodicity was estimated by a maximum entropy method of Fourier transformation. The results indicated that a fragment from 3101-st to 3200-th residues of dystrophin contains several transmembrane helices. The hydropathy plot of this region strongly suggests four transmembrane helices, indicating that both ends, N-and C-termini, are located in the cytoplasmic sides with firm anchoring into membrane by these helices.

Amino Acid Sequence↗
PubMed1993

Bioactive compounds from the buds of Platanus orientalis and isolation of a new kaempferol glycoside.

A new compound kaempferol 3-O-alpha-L-(2"-E-p-coumaroyl)-rhamnopyranoside, as well as the known flavonoids, kaempferol 3-O-beta-D-(6"-E-p-coumaroyl)-glucopyranoside, kaempferol 3-O-alpha-L-(2",3"-di-E-p-coumaroyl)-rhamnopyranoside, and caffeic acid were obtained from the methanolic extract of Platanus orientalis L. buds. All the compounds were isolated by column chromatography and identified using 1H-NMR, 2D-1H-NMR (COSY), 1H-13C-NMR, and CIDMS techniques. Cytotoxic and antimicrobial studies were carried out in vitro against human cell lines and against Gram-positive and Gram-negative organisms.

Anti-Infective Agents↗
PubMed1993

Kinetic analysis of the denaturation process by alcohols of sodium channels in squid giant axon.

1. The effects of several aliphatic alcohols on sodium currents were examined in the intracellularly perfused squid giant axon when the same concentration of alcohol was applied on both sides of the membrane. 2. An irreversible suppression of sodium currents, accompanied by anaesthesia at high alcohol concentration, was examined in detail using four aliphatic alcohols, that is, ethanol, 1-propanol, 1-butanol and 1-pentanol. 3. This irreversible effect seemed to be attributable to the sequential denaturation of sodium channels, because the kinetics, the current-voltage relation and the sodium channel activation-voltage curve did not change after the sodium current decreased. 4. The time course of the remaining sodium conductance was measured as a function of the sum of the alcohol application time by repeating the process of applying and completely washing out alcohol. The remaining sodium conductance decayed as a function of time in a single exponential manner. This decay time constant depended strongly on the concentration of alcohol and could be assumed to be the denaturation time constant of the sodium channel. 5. The denaturation time constant decreased as the alcohol concentration increased. This time constant is proportional to the Nth power of the alcohol concentration. The N values are 4.3, 4.5, 5.8 and 7.6 for ethanol, 1-propanol, 1-butanol and 1-pentanol, respectively. This implies that alcohol molecules bind to a restricted number of specific sites in the sodium channel protein to cause the denaturation. 6. The concentration of alcohol which caused the same amount of denaturation is related to the exponential function of the carbon number of the alcohol. Considering the partition coefficient of alcohol between lipid and aqueous solution, the concentration of alcohol in the membrane which denatured half of the sodium channels in 2 h can be calculated to be 0.5 M for all alcohols.

Action Potentials↗
PubMed1991

Hydrophobic core of molten-globule state of bovine carbonic anhydrase B.

The interaction which stabilizes the intermediate state of the protein folding and/or unfolding is important for understanding the structure formation mechanism of proteins. The partitioning of a hydrophobic fluorescence probe, pyrene, into the core of a 'molten globule' structure of bovine carbonic anhydrase B was measured, revealing a partition coefficient of about 10(4). The result leads to the conclusion that the compact structure of the molten-globule state is formed by the hydrophobic interaction, as detergent micelles are formed by the same interaction.

Animals↗
PubMed1989

A theoretical method for distinguishing between soluble and membrane proteins.

A method for distinguishing between membrane and soluble proteins in an amino acid sequence was developed, using only two parameters associated with the hydrophobicity: the average hydrophobicity and the power spectral density of period longer than 30 residues. The power spectral density was calculated by a maximum entropy method of Fourier transformation. Membrane proteins could be distinguished from soluble proteins with a distinction rate as high as 97%. This fact strongly suggests that the morphology of proteins, i.e., membrane or soluble forms, is determined thermodynamically through the hydrophobicity of polypeptides.

Amino Acid Sequence↗
PubMed1989

[Plants from New Caledonia. Alkaloids from Sarcomelicope dogniensis Hartley stem bark].

Two new pyranofuroquinoline alkaloids, cis-1,2-dihydroxy-1,2 dihydroacronydine 2 and trans-1,2-dihydroxy-1,2-dihydroacronydine 3 have been isolated from Sarcomelicope dogniensis stem bark. Their structures have been elucidated by spectral analysis and chemical correlations. In addition, 11 other alkaloids have been isolated from the stem bark of this species.

Alkaloids↗
PubMed1989

[Polyphenolic glycosides from Cistus creticus L. leaves].

Five flavonoids: kaempferol 3-O-beta-D-glucopyranoside, quercetin 3-O-beta-D-glucopyranoside, quercetin 3-O-beta-D-rutinoside, myricetin 3-O-alpha-L-rhamnopyranoside, myricetin 3-O-beta-D-galactopyranoside and one coumarin: esculin have been isolated from the leaves of Cistus creticus. Their structures have been elucidated on the basis of their spectral data mainly mass spectrometry (DCI) and 1H NMR.

Chemical Phenomena↗
PubMed1988

Denaturation of bacteriorhodopsin by organic solvents.

The denaturation of bacteriorhodopsin by various organic solvents was studied using absorption, circular dichroism (CD) and fluorescence measurements. Organic solvents with a hydrogen-bonding group caused the release of retinal. The CD measurements showed that the helical structure was maintained even in the denatured state, whereas its tertiary structure was destroyed. The change in fluorescence intensity of tryptophan and fluorescent retinal also confirmed that the tertiary structure was destroyed. Comparison of the denaturation efficiency of various organic solvents showed that the concentration at denaturation was inversely proportional to the partition coefficient of the denaturant. This inverse proportionality clearly indicated that denaturation was determined by the concentration of denaturants which partitioned into the hydrophobic region of the membrane. It was discussed from the experimental results that the tertiary structure of bacteriorhodopsin was stabilized by the hydrogen-bonding networks between side chains of the helices. The results obtained from analysis of the amino acid sequence were also consistent with the hydrogen-bonding mechanism for the formation of the tertiary structure.

Journal Article↗
PubMed1985

Interaction between Ca2+ and dipalmitoylphosphatidylcholine membranes. I. Transition anomalies of ultrasonic properties.

The effect of Ca2+ on a gel-to-liquid crystal transition as well as the mechanical properties of dipalmitoylphosphatidylcholine bilayers was studied by an ultrasonic technique. Transition temperature increased with increase in Ca2+ concentration, whereas the variation of ultrasonic anomalies indicated that dipalmitoylphosphatidylcholine bilayers exhibited maximum pseudocritical fluctuation at a Ca2+ concentration of about 10 mM. Hardening of dipalmitoylphosphatidylcholine membranes due to the Ca2+ binding was observed above 10 mM CaCl2, suggesting the lateral compression of the lipid bilayer by bound Ca2+. Long-range attraction between bound Ca2+ and the head groups of surrounding lipid molecules was proposed from these calcium effects.

Calcium↗
PubMed1985

Interaction between Ca2+ and dipalmitoylphosphatidylcholine membranes. II. Fluorescence anisotropy study.

The effect of Ca2+ on the molecular mobility in dipalmitoylphosphatidylcholine membranes was studied by steady-state and time-resolved measurements of fluorescence anisotropy. The fluorescence anisotropy decay of 1,6-diphenyl-1,3,5-hexatriene in the hydrocarbon region indicated that the free volume of molecular rotation became more restricted when the Ca2+ concentration was increased. The decrease of the molecular mobility was observed from 1 mM Ca2+, at which the number of bound Ca2+ is much less than that of the total lipid molecules. A distinct difference between Ca2+ and Mg2+ effects suggested that the change in various membrane properties was induced by the binding of these ions. From these results we propose a long-range attractive interaction between bound Ca2+ and the polar head groups of distant phosphatidylcholine molecules.

Calcium↗
PubMed1984

Localization of the galactoside binding site in the lactose carrier of Escherichia coli.

The location of flurophores specifically bound to the lactose/H+ carrier of Escherichia coli was ascertained by the use of various collisional quenchers. The reporter groups were (1) the pyrenyl residue of N-(1-pyrenyl)maleimide attached to the essential cysteine residue 148, which is presumably at or near the galactoside binding site, and (2) the dansyl moieties of a series of fluorescent substrate molecules. The accessibility of these fluorophores from the lipid phase was assessed by nitroxyl-labelled fatty acids and phospholipids. By using a series of nitroxyl-labelled fatty acids carrying the quencher at different positions in the acyl chain, the position of a quenchable fluorophore with respect to the membrane normal can be determined. The accessibility of fluophores from the aqueous phase was assessed by using a water-soluble quencher, the N-methylpicolinium ion. The results of quenching studies suggest that the galactoside binding site is located within the carrier and that this binding site communicates with the aqueous phase through a pore.

Affinity Labels↗
PubMed1983

Thermodynamic properties of the lipid bilayer transition. Pseudocritical phenomena.

Ultrasonic relaxation of multilamellar liposomes formed from dipalmitoylphosphatidylcholine was measured near the gel-to-liquid crystal transition by a differential ultrasonic resonator. The relaxation time and strength increased remarkably near the transition temperature, indicating a pseudocritical phenomenon. A quantitative analysis of the relaxation in terms of thermodynamic relationships between specific heat, thermal-expansion coefficient, and compressibility showed that more than 90% of the total endothermic heat of the transition arises from the latent heat. The temperature dependence of the ultrasonic relaxation parameters was also analyzed by the Landau theory; we obtain a small but finite difference, 0.6 degree C, between the pseudocritical temperature and the transition temperature. These results provide a quantitative description of both the first-order and second-order characters of the gel-to-liquid crystal transition.

Gels↗
PubMed1982

Anomalies of nanosecond ultrasonic relaxation in the lipid bilayer transition.

The frequency dependence of ultrasonic velocity as well as absorption in a suspension of sonicated dipalmitoylphosphatidylcholine vesicles was measured by a differential ultrasonic resonator. The frequency was scanned between 1.3 and 13 MHz and the temperature was varied from 25 to 47 degrees C. A pronounced relaxation was observed in the time range of 10 ns. The data were analyzed assuming a single relaxation which appeared to be a good approximation. The relaxation time as well as relaxation strength increased anomalously in the vicinity of the gel-to-liquid crystal transition of 41.5 degrees C. This result represents the first definite evidence of the critical slowing down in the lipid bilayer and is discussed in terms of the Landau theory of phase transition. The possible biological significance of the mechanical relaxation is also presented.

Kinetics↗
PubMed1982

Effect of calcium ion on the mechanical properties of lipid bilayer membrane.

Elastic properties of dipalmitoyl phosphatidylcholine bilayers were studied by an ultrasonic technique as a function of the concentration of calcium ion. The ultrasonic velocity showed a broad minimum at about 10 mM CaCl2, indicating that the bulk modulus of membrane is smallest at this calcium ion concentration. Since the amount of calcium ions adsorbed to the membrane monotonously increases, calcium ions have two kinds of effects on the phosphatidylcholine membrane, namely softening effect at lower concentration and hardening at higher concentration. It is suggested that the softening is due to some structural change of hydrated water and the hardening is due to chelation of lipid molecules by adsorbed calcium ions. The estimation of bulk modulus and Young's modulus revealed that Young's modulus and rigidity are much smaller than the bulk modulus even in the gel phase.

Calcium↗