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Biomedical subjects

N Kamo

Publications and source records attributed to N Kamo.

At least 73 records · Page 4Linked to original sources
PubMed1991

Glucose transport of Haloferax volcanii requires the Na(+)-electrochemical potential gradient and inhibitors for the mammalian glucose transporter inhibit the transport.

The uptake of glucose and its non-metabolizing analogues by Haloferax volcanii, one of the glucose-utilizing Halobacteria, was examined using intact cells and envelope vesicles. Results obtained were: (1) The transport system is inducible. (2) The uptake requires the gradient of Na(+)-electrochemical potential. (3) Inhibitors for mammalian glucose transport also have an effect on this system, implying that the transporters resemble each other. (4) It is suggested that the mobility of the transporter is regulated by the membrane energization.

Biological Transport, Active↗
PubMed1991

Photoreaction cycle of phoborhodopsin studied by low-temperature spectrophotometry.

The photochemical and subsequent thermal reactions of phoborhodopsin (pR490), which mediates the negative phototaxis (phobic reaction) of Halobacterium halobium, were investigated by low-temperature spectrophotometry. At room temperature, the absorption spectrum of pR490 displayed vibrational structure with a maximum at 490 nm and a shoulder at 460 nm, which were remarkably sharpened by cooling, resulting in the appearance of two well-separated peaks. On irradiation of pR490 at -170 degrees C, a photo-steady-state mixture composed of pR490 and two photoproducts, P520 and P480, was formed. P480 had an absorption maximum at 480 nm and thermally converted to pR490 above -160 degrees C, while P520 had an absorption maximum at 515 nm and thermally converted to P350, the next intermediate, above -60 degrees C. Above -30 degrees C, P350 was converted to P530, and then reverted to pR490. P520, P350, and P530 may correspond to K, M, and O intermediates of bacteriorhodopsin, respectively, on the basis of their absorption spectra, but the intermediates corresponding to L and N intermediates were not observed. On the basis of these results, a new scheme of the photoreaction cycle of pR490 was presented.

Archaeal Proteins↗
PubMed1990

Latex piezoelectric immunoassay: detection of agglutination of antibody-bearing latex using a piezoelectric quartz crystal.

A method for immunoassay of CRP (C-reactive protein) was developed using a piezoelectric quartz crystal. Previous immunoassays using a piezoelectric crystal have required the formation of a thin film on the crystal, to which an antibody is affixed. The occurrence of antigen-antibody reaction increases the weight attached to the crystal surface, which causes a reduction in the oscillation frequency. In our method, the frequency reduction was observed using antibody-bearing latex without any film. One possible mechanism of the frequency change is that the crystal acts as a sensing apparatus for viscosity or density change in the solution due to aggregation of latex particles. The detection limit was almost the same as that for latex photometric immunoassay (LPIA). The present method has been designated as latex piezoelectric immunoassay (LPEIA).

Agglutination Tests↗
PubMed1989

Plasma-polymerized membrane electrode for the determination of dextromethorphan and dimemorfan.

Ion-selective electrodes (ISEs) responsive to the antitussives dextromethorphan and dimemorfan were constructed by the fixation of an ion-exchanger, ammonium tetraphenylborate, on a Millipore membrane by means of a plasma-polymerization technique. The electrodes showed a Nernstian response over the range of 10(-5)-10(-2) M dextromethorphan and dimemorphan, and the working pH range was 5-7. The interference from common cations such as Na+, K+ and Ca2+ was negligible but some organic cations interfered weakly. The electrodes were applied successfully for the determination of the drugs in pharmaceutical preparations.

Dextromethorphan↗
PubMed1988

On the glutamate transport through cell envelope vesicles of Halobacterium halobium.

Glutamate uptake by envelope vesicles of Halobacterium halobium was measured. Previous authors showed that the glutamate uptake needs the illumination as well as Na+ gradient across the membrane. The latter is considered to be the driving force for the uptake. No satisfactory explanation for the necessity of the illumination has not been given. We found that in the absence of Cl- in the medium, only Na+ gradient was enough to induce the glutamate uptake, i.e. no illumination was needed. Glutamate uptake was measured with various strains of H. halobium. We found that the envelope vesicles prepared from strains containing no bacteriorhodopsin showed the glutamate uptake in the dark and in the presence of Cl- in the medium provided only that Na+ gradient is imposed.

Cell Membrane↗
PubMed1987

Mitochondrial membrane potential estimated with the correction of probe binding.

Lipophilic ions are widely used as the probe for estimation of the membrane potential. It is suggested that the correction of the probe binding to the membrane and/or intracellular constituents is a problem to be solved in order to evaluate the membrane potential accurately. Previously, we proposed a method for the correction of the probe binding (Demura, M., Kamo, N. and Kobatake, Y. (1985) Biochim. Biophys. Acta 820, 207-215). In this paper, the method was applied to the determination of the membrane potential of intact mitochondria. The probes used constitute a homologous series of (Phe)3-P+-(CH2)n-CH3 (n = 0-4) and tetraphenylphosphonium (TPP+). Binding of these probes to de-energized mitochondria followed the Langmuir isotherm. However, values of parameters determined at high (50-800 microM) and low (under 20 microM) probe concentrations were different, suggesting the existence at least two, high- and low-affinity, binding sites. With extrapolation to the 'state of no binding', the membrane potential of intact mitochondria was estimated to be -147 mV (interior-negative) when they were energized by 5 mM succinate in medium consisting of 125 mM KCl, 10 mM MgCl2, 5 mM phosphate, 0.4 mM EDTA and 50 mM Tris-HCl (pH 7.5) at 25 degrees C. Parameters appearing in the equation for the correction of probe binding were determined with the use of this value of the membrane potential. The validity of the equation and the value of the parameters were revealed by the fact that after the correction, all probes used gave approximately the same value under the same conditions. We expanded the method so as to include the langmuir adsorption isotherm. When the modified equation is used, the estimated membrane potentials were less dependent on a probe concentration less than 10 microM.

Animals↗
PubMed1987

Binding of lipophilic cations to the liposomal membrane: thermodynamic analysis.

Lipophilic ions are widely used as probes for measuring membrane potentials. Since binding of the probes to the membrane interferes with the accurate estimation of the membrane potential, it is necessary to clarify the characteristics of probe binding to membranes. The present paper deals with the binding of lipophilic cations to liposomes. The results can be summarized as follows: (1) The binding of triphenylmethylphosphonium, its homologues and tetraphenylphosphonium to liposomes of dipalmitoylphosphatidylcholine followed the Langmuir adsorption isotherm. (2) Spin-labeled lipophilic cations were synthesized and the binding to liposomes of egg phosphatidylcholine was examined. The binding also followed the Langmuir adsorption isotherm. The dissociation constant (the concentration giving half-maximal binding), K, was independent of the temperature, indicating that the binding is entropy-driven. (3) The binding was influenced by the fluidity of the membrane. Except in the case of triphenylmethylphosphonium (TPMP+), K and A (maximum amounts of binding) increased above the transition temperature. In other words, above the phase transition temperature the binding affinity is decreased, while maximum amounts of binding are increased for all phosphoniums used except TPMP+.

Adsorption↗
PubMed1986

Flash spectrophotometric identification of a fourth rhodopsin-like pigment in Halobacterium halobium.

A fourth retinal-containing pigment in Halobacterium halobium cell membrane was examined by flash spectrophotometry. The absorption maximum of this pigment was at about 480 nm. Flash light caused a photoreaction cycle with a half recovery time of about 300 ms at room temperature. The photoreaction cycle involved at least two photo-intermediates. The absorption maximum of the first one was at about 350 nm and that of the second was at around 530 nm. The spectral properties of this pigment and the content of the cells correlate with the sensitivity of photo-repellent response to the light around 480 nm. We suggest a name 'phoborhodopsin' for this new pigment.

Halobacterium↗
PubMed1986

Role of the valence of concanavalin A in the activation of guinea pig polymorphonuclear leukocytes.

Stimulation of polymorphonuclear leukocytes (PMN) by tetravalent concanavalin A (alpha-ConA) induces membrane depolarization preceding the onset of superoxide anion (O2-) production. Both divalent and monovalent ConA analogues were studied to evaluate the role of valence. Monovalent ConA (m-ConA) was inactive in stimulating O2- production and divalent derivatives were less active than native alpha-ConA. Similarly, membrane depolarization was dependent on the valency of ConA. m-ConA did not induce a marked change in membrane potential, whereas sustained depolarization occurred with multivalent ConA. The formation of multiple linked interactions between surface receptors may be an important early event in the activation of PMN by ConA.

Animals↗
PubMed1985

Evidence that the long-lifetime photointermediate of s-rhodopsin is a receptor for negative phototaxis in Halobacterium halobium.

The effect of blue background light on behavioral response of Halobacterium halobium to step-like stimulation with green-orange attractant light was examined. The results strongly support the previously proposed hypothesis that a long-lifetime photointermediate of s-rhodopsin is the photoreceptor for repellent light: the step-like increase in green-orange light was convertible from attractant stimulus to repellent one, when the cells were constantly illuminated with blue light. No difference of the threshold intensity of the blue background light was observed between the mutant strain that lacks both bacteriorhodopsin and halorhodopsin and the wild type strain, suggesting that the two light-driven ion pumps are not participant in sensing attractant light.

Halobacterium↗
PubMed1985

Light and dark adaptation of halorhodopsin.

Dark incubation of envelope vesicles derived from a strain of Halobacterium halobium that lacks bacteriorhodopsin but contains halorhodopsin and a third rhodopsin-like pigment caused a decrease in the flash yield [the amplitude of a transient absorbance change of flash reactive component(s) by flash] of halorhodopsin but not the rhodopsin-like pigment. The flash yield decreased to reach a low steady level after incubation for about 4 days in the dark. The flash yield of halorhodopsin at any stage of dark incubation was increased by actinic illumination of the vesicles. The flash yield at 490 nm (absorbance increase) was found to be approximately proportional to that at 590 nm (absorbance decrease). These results indicate that halorhodopsin in the envelope vesicles has two forms, dark and light adapted, and that the halorhodopsin phototransient absorbing at 490 nm is originated from the light-adapted form. A difference spectrum between these two forms of halorhodopsin shows that the light-adapted halorhodopsin was red-shifted from the dark-adapted form. The light-induced membrane potential was measured by tetraphenylphosphonium uptake. The uptake by the dark-adapted vesicles was slower than that by the light-adapted vesicles, suggesting that only the light-adapted halorhodopsin has ion-transporting activity.

Adaptation, Biological↗
PubMed1984

Photochemical intermediate of third rhodopsin-like pigment in Halobacterium halobium by simultaneous illumination with red and blue light.

We found new photochemical intermediate of third rhodopsin-like pigment (tR) or slow cycling rhodopsin-like pigment (sR) in Halobacterium halobium, which was produced by simultaneous illumination with red and blue light. This illumination is employed for measurements of negative phototaxis. The formation of this intermediate is fast. (With the instrument used, it could not be measured.) The half-time of its decay is ca 150 msec in 4 M NaCl, pH 7.0 at 20 degrees C. The maximum of absorbance is located at 510-530 nm.

Bacteriorhodopsins↗
PubMed1984

Suggestion of existence of two forms of halorhodospin in alkaline solution.

Illumination of halorhodopsin (hR590) with orange light in alkaline solution produced a 410 nm absorbing species (hR410), which returned to hR590 upon blue light illumination. The amount of the flash-reactive species of hR590 was estimated by the flash-yield. Illumination with orange light decreased the flash yield, due to the formation of hR410. Blue light illumination of this sample led to the increase of the yield, which was larger than that before orange light illumination. In dark, the yield decreased gradually in 3-4 days. The scheme is proposed in which there exist two forms of hR590.

Bacteriorhodopsins↗
PubMed1984

Effect of salt on photocycle and ion-pumping of halorhodopsin and third rhodopsinlike pigment of Halobacterium halobium.

The cytoplasmic membranes of Halobacterium halobium contain at least three retinal pigments: bacteriorhodopsin (bR), halorhodopsin (hR), and a third rhodopsinlike pigment (tR). The amplitudes of the phototransient in the photolysis of hR and tR were measured in various salt solutions. Halogen ion (except fluoride) was required to retain the photocycle of hR. Parallels between the amplitude of the phototransient of hR and the magnitude of the photo-induced tetraphenylphosphonium (TPP+) uptake suggests that hR is a light-driven halogen pump, which supports the hypothesis by Schobert and Lanyi (J. Biol. Chem., 1982, 257:10306-10313). The order of effectiveness of halogen was Br- greater than Cl- greater than I-. On the other hand, no specific ion was required to retain the photocycle of tR, and tR was concluded to be nonelectrogenic.

Anions↗
PubMed1983

Light-induced delta pH of envelope vesicles containing halorhodopsin measured by use of a spin probe.

The spin-labeled amine, 4-amino-2,2,6,6-tetramethyl-piperidino-N-oxyl was used to measure the photoinduced delta pH in the envelope vesicles derived from mutant cells of Halobacterium halobium. The cells contain halorhodopsin (hR) and are spectroscopically free from bacteriorhodopsin (bR). The EPR signals from the extravesicular populations of the probe was quenched by ferricyanide. The membrane bound population of the probe was less than 1% of the amount of the probe entrapped within the vesicle. Hence, we can monitor continuously the concentration of the intravesicular populations of the probe and delta pH can be calculated from the line height of the signal. The kinetic analysis indicated that the time course of the change in the EPR signal represents faithfully delta pH of the vesicle. At pH 7.5, the photoinduced delta pH showed a maximum. The kinetic constant of pH change also displayed a peak at this pH. Addition of uncoupler did not increase either the rate nor magnitude of delta pH at this pH, but at other pH, especially at lower pH, uncoupler showed its effect. A theoretical equation was derived which correlated the photocycle of hR with delta pH. According to the analysis by use of this equation, the time constant of the photocycle was suggested to be constant in pH ranging from 5.5 to 8.25. The maximum in photoinduced delta pH observed at pH 7.5 was concluded to be due to the permeability dependence of ions, especially of H+ on pH. The temperature dependence of delta pH was measured. As the temperature decreased, delta pH was, surprisingly, found to be increased. The rate constant of the photocycle analyzed by the equation, however, decreased with decrease of temperature.

Bacterial Proteins↗
PubMed1983

Photochemistry of two rhodopsinlike pigments in bacteriorhodopsin-free mutant of Halobacterium halobium.

Two photocycles due to two different pigments were found in membrane vesicles of a bacteriorhodopsin-free mutant of Halobacterium halobium. A pigment absorbing approximately 590 nm halorhodopsin (HR) underwent a faster photocycle with a phototransient at approximately 490 nm (half-time of decay, tau 1/2 = 10 ms). Another third rhodopsinlike pigment (TR) absorbing approximately 580 nm underwent a slower photocycle accompanying a phototransient absorbing below 410 nm (tau 1/2 = 0.8s). The photocycles were measured under various conditions of temperature, NaCl concentration, pH, and in the presence of cholate. All results obtained support the notion that the two photocycles are independent of each other, and the fast or the slow cycle can be abolished after these treatments. At alkaline pH, the wavelength of maximum absorbance of both pigments shifted to blue, but the magnitude of the shift of the pigment undergoing the slow photocycle was much greater than the other. The ratio of the content of the two pigments varies among bacteriorhodopsin-free mutants.

Bacteriorhodopsins↗