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S Kikkawa

Publications and source records attributed to S Kikkawa.

At least 37 records · Page 2Linked to original sources
PubMed1996

Simple purification and functional reconstitution of octopus photoreceptor Gq, which couples rhodopsin to phospholipase C.

In invertebrate photoreceptors, illuminated rhodopsin activates multiple G proteins, which are assumed to initiate multiple phototransduction cascades. In this paper, we focused on one of the phototransduction cascades, which utilizes rhodopsin, a Gq-like G protein, and phospholipase C (PLC). A Gq-like G protein from octopus photoreceptors was successfully purified to apparent homogeneity as an active form by simple two-step chromatography. The purified G protein had an alpha beta gamma-trimeric structure consisting of 44-kDa alpha, 37-kDa beta, and 9-kDa gamma subunits. The 44-kDa alpha subunit was assigned to the Gq class by western blot with antiserum against mammalian Gq alpha and by partial amino acid sequencing of its proteolytic fragments. Light-dependent binding of GTP gamma S was observed when the purified octopus Gq was reconstituted with octopus rhodopsin that had been integrated into phospholipid vesicles. Octopus Gq activated PLC beta 1 purified from bovine brain dose-dependently in the presence of A1F4-. Finally, light- and GTP-dependent activation of PLC beta 1 was observed in a reconstitution system consisting of octopus rhodopsin, Gq, and bovine PLC beta 1.

Aluminum Compounds↗
PubMed1994

Synaptic connection patterns between frog retinal ganglion cells and tectal neurons revealed by whole-cell recordings in vivo.

The synaptic connections between frog retinal ganglion cells and tectal neurons were examined by whole-cell recordings in vivo combined with nystatin perforated patch-clamp technique and pulse-triggered averaging analysis. In five tectal neurons, monosynaptic EPSPs from seven R3 retinal ganglion cells were observed. One tectal neuron was found to receive EPSPs from both R1/2 and R3 retinal ganglion cell simultaneously. Thus we could provide the first evidence for convergence of multiple types of retinal axons upon a single tectal neuron.

Animals↗
PubMed1993

GTP-binding protein couples with metabotropic glutamate receptor in bovine retinal on-bipolar cell.

GTP-binding protein (G protein) linking to metabotropic glutamate receptor of bovine retinal on-bipolar cell was studied by use of pharmacologically selective ligands, 2-amino-4-phosphonobutyric acid (APB) on bacterial toxin-catalyzed ADP-ribosylation and GTP gamma S-binding. In contrast to the electrophysiological findings reported, G protein coupling to APB-sensitive glutamate receptor served as a substrate for pertussis toxin but did not for cholera toxin. Several glutamate analogues effective on on-bipolar cell, as well as APB, increased GTP gamma S binding to retinal membranes devoid of rod outer segments. The enhancement of GTP gamma S binding by APB was completely abolished when the membranes were pretreated with pertussis toxin and NAD. These results suggest that, in retinal on-bipolar cell, the G protein which couples metabotropic glutamate receptor to hyperpolarizing response of the cell is sensitive to pertussis toxin.

Animals↗
PubMed1992

Activation of nucleoside diphosphate kinase by mastoparan, a peptide isolated from wasp venom.

We have previously reported that GDP-bound alpha beta gamma-trimeric GTP-binding (G) proteins can be converted into the active GTP-bound form with nucleoside diphosphate (NDP) kinase and ATP, although its exact activation mechanism still remains to be resolved. In the present study, we investigated whether NDP kinase activity was modified by mastoparan, a wasp venom peptide that is known to activate G proteins as an agonist-receptor complex. The activity of NDP kinase measured by the formation of GTP from ATP and GDP was markedly stimulated, when the kinase was incubated with mastoparan. The concentration of mastoparan required for the activation was much lower than that observed for the peptide-induced activation of G proteins under similar assay conditions. There was also an increase in the phosphorylated intermediate of NDP kinase as well as the catalytic activity upon its incubation with mastoparan. These results suggest that mastoparan not only activates G proteins directly via guanine nucleotide exchange reaction but also stimulates NDP kinase activity.

Animals↗
PubMed1992

Superoxide dismutase and glutathione in the gastric mucosa of patients with chronic liver disease.

The total activity of superoxide dismutase and glutathione peroxidase and the tissue content of Cu,Zn-superoxide dismutase, glutathione, and lipoperoxides in the gastric mucosa were determined in patients with chronic liver disease and in healthy controls. The mean levels of Cu,Zn-superoxide dismutase in liver cirrhosis and in hepatocellular carcinoma with cirrhosis were significantly reduced compared to controls (32.0 +/- 4.4, and 35.8 +/- 2.2, vs 44.6 +/- 2.2 ng/mg protein, p < 0.01). Mucosal levels of glutathione were significantly lower in chronic active hepatitis, liver cirrhosis, and hepatocellular carcinoma with cirrhosis than in controls (9.7 +/- 2.1, 8.9 +/- 2.3, and 11.0 +/- 3.4, vs 23.6 +/- 4.7 nmol/mg protein, p < 0.05). However, there were no significant differences between chronic liver disease and controls in the activity of gastric superoxide dismutase and glutathione peroxidase. Gastric lipoperoxide concentrations were significantly higher in chronic active hepatitis, liver cirrhosis, and hepatocellular carcinoma with cirrhosis than in controls (0.56 +/- 0.07, 0.50 +/- 0.12, 0.50 +/- 0.05 vs 0.18 +/- 0.03 nmol/mg protein, p < 0.05). These results suggest that the concentrations of gastric mucosal antioxidants were decreased in chronic liver disease, and that these changes may be responsible for the higher frequency of gastric mucosal lesions observed in patients with chronic liver disease.

Aged↗
PubMed1991

Turbulence in the canine ascending aorta and the blood pressure.

Turbulent velocity fluctuations were measured and analyzed in the canine ascending aorta using a hot-film anemometer. Blood flow rate and temperature were stabilized using a special bypass technique. Blood pressure was elevated by Methoxamine infusion. Turbulence components were extracted from measured data using an ensemble averaging technique. Turbulence intensity correlated best with blood flow rate although the variance was relatively large, especially when the blood flow velocity was high. When pooled data were grouped into subclasses using peak aortic flow velocity as the criteria, turbulence intensity correlated well with aortic systolic blood pressure in each of the subclasses. Spectral bandwidth correlated with aortic pressure in the same manner. In summary, turbulence in the aorta developed when blood pressure was high. Both an increase of turbulence intensity and an widening of turbulence spectra may be ascribed to a stiffening of the aortic wall due to an elevation of blood pressure.

Animals↗
PubMed1990

Conversion of GDP into GTP by nucleoside diphosphate kinase on the GTP-binding proteins.

A direct interaction of alpha beta gamma trimeric GTP binding proteins (G proteins; G0 and Gs) with nucleoside diphosphate kinase (NDP kinase) was investigated with homogeneously purified proteins. There was a progressive release of 32Pi from [gamma-32P]ATP when GDP-bound G0 was incubated together with NDP kinase. The Pi release induced by the interaction of G0 with NDP kinase was not accompanied by the dissociation of GDP bound to the alpha-subunit of G0. This was a sharp contrast to G protein-catalyzed GTP hydrolysis observed with GTP as the substrate; the dissociation of bound GDP was essentially required for the following binding of the substrate, GTP, to be hydrolyzed. A kinetic analysis displayed different properties for the substrate of NDP kinase between free GDP and G protein-bound GDP. NDP kinase-dependent phosphorylation of GDP on G0 was indeed demonstrated with adenosine 5'-(3-O-thio)triphosphate as the phosphate donor; there was a formation of guanosine 5'-(3-O-thio)triphosphate-bound G0 from the ATP analogue. Moreover, purified Gs was readily ADP-ribosylated by cholera toxin in the presence of NDP kinase, ATP, and an ADP-ribosylation factor, also suggesting that the nucleotide form on Gs was certainly GTP. These results indicate that NDP kinase can transfer the gamma-phosphate of ATP directly to GDP bound to G proteins and that this phosphorylation results in the activation of the signal-coupling proteins. A possible role of the new activation mechanism of G proteins is discussed in comparison with the previously characterized GDP-GTP exchange pathway by the agonist-receptor complex.

Adenosine Triphosphate↗
PubMed1990

Identification of sites for alkylation by N-ethylmaleimide and pertussis toxin-catalyzed ADP-ribosylation on GTP-binding proteins.

An alpha beta gamma-trimeric GTP-binding protein (Go) serving as the substrate of pertussis toxin-(IAP) catalyzed ADP-ribosylation was purified from rat brain membranes. The constituent alpha-subunit (alpha o) was alkylated with N-ethylmaleimide (NEM), and the functionally important sulfhydryl groups were investigated. There were at least two cysteine residues highly reactive to NEM on the GDP-bound form of alpha o. These alkylations resulted in loss of its ability to be ADP-ribosylated by IAP and to associate with beta gamma, but leaving the GTP-binding site of alpha o intact. The reacted cysteine residues were identified by the sequencing of tryptic fragments of alpha o. One of the alkylation sites was Cys-351, which was four amino acid residues away from the carboxyl-terminus of the molecule. The Cys-351 was proven to be also a site for IAP-catalyzed ADP-ribosylation. Possible roles of cysteine residues on the alpha-subunit of Go are discussed in the functions of the signal transducing protein.

Adenosine Diphosphate Ribose↗
PubMed1989

Purification of GTP-binding proteins from bovine brain membranes. Identification of heterogeneity of the alpha-subunit of Go proteins.

Using high-resolution Mono Q column chromatography, we purified 6 distinct peaks of GTP-binding proteins from bovine brain membranes. Five of them consisted of 3 polypeptides with alpha beta gamma-subunits and served as the substrate of islet-activating protein (IAP), pertussis toxin. The other one was purified as alpha-subunit alone and was also ADP-ribosylated by IAP in the presence of beta gamma-subunits. When each alpha-subunit was characterized by immunoblot analysis using various antibodies with defined specificity, the two of them were identified as Gi-1 and Gi-2, and other 4 appeared to be Go or Go-like G proteins. The alpha-subunits of immunologically Go-like proteins were apparently distinguishable from one another on elution profiles from the Mono Q column. Thus, there was a heterogeneity of the alpha-subunit of Go in the brain membranes.

Animals↗
PubMed1989

Real-time and simultaneous measurement of tricuspid orifice and tricuspid anulus areas in anesthetized dogs.

Tricuspid valve orifice and tricuspid valve anulus areas were measured simultaneously in the anesthetized dog with a newly developed area-measuring system based on electromagnetic induction. This system permitted real-time monitoring of the area enclosed by the edges of valve leaflets and by the juncture of the valve leaflet and the cardiac wall in situ, without artificial constraint to the valve motion. Right atrial and right ventricular pressures were measured with two catheter-tipped micromanometers. During control state, tricuspid valve orifice area (TOA) increased up to its peak [1.38 +/- 0.26 cm2 (mean +/- SD)] coincidently with either atrial systole or rapid ventricular filling. Atrial contraction evoked distinct presystolic tricuspid anulus narrowing with concomitant slow TOA reduction. This slow TOA reduction began 30.0 +/- 16.1 msec before systolic atrioventricular pressure crossover, and the following rapid TOA decrease was completed 38.7 +/- 12.2 msec after systolic atrioventricular pressure crossover. TOA began to increase 48.4 +/- 30.4 msec before diastolic atrioventricular pressure crossover at the end portion of the isovolumic relaxation phase, opposing residual transvalvular pressure gradient (3.33 +/- 1.79 mm Hg). The slow presystolic TOA decrease was considered to be a reflection of the presystolic anulus narrowing caused by atrial systole. An isolated atrial contraction induced by administering 1 mg acetylcholine chloride into the atrioventricular node artery or by vagus nerve stimulation could produce complete valve closure. Even in an isolated atrial contraction, the inflection point that marks the boundary between slow "atriogenic" closure presumably due to anulus narrowing and rapid closure presumably due to hemodynamic force was easily identified.

Animals↗
PubMed1989

Esterification of chiral secondary alcohols with fatty acid in organic solvents by polyethylene glycol-modified lipase.

Lipase from Pseudomonas fragi 22.39B was modified with polyethylene glycol. The modified lipase (PEG-lipase) was soluble and active in organic solvents such as benzene and 1,1,1-trichloroethane. PEG-lipase catalyzed esterification of chiral secondary alcohols with fatty acids in benzene and exhibited preference for R isomers over S isomers. Km and Vmax values for each isomer of various alcohols were obtained by kinetic study of the esterification in benzene. PEG-lipase-catalyzed esterification leads to optical resolution of a racemic alcohol.

Alcohols↗
PubMed1988

Spectrum analysis of turbulence in the canine ascending aorta measured with a hot-film anemometer.

We measured turbulence velocity in the canine ascending aorta using a hot-film anemometer. Blood flow velocity was measured at various points across the ascending aorta approximately 1.5-2 times the diameter downstream from the aortic valve. The turbulence spectrum was calculated and its characteristics were examined in connection with the mean Reynolds number and/or measuring positions. In the higher wave number range the values of the turbulence spectra were higher at larger mean Reynolds number. In the higher wave number range, the values of the turbulence spectra were higher at points closer to the centerline of the aorta, when the mean Reynolds number was relatively large. The patterns of the turbulence spectra at various points outside the boundary layer on the aortic wall were similar.

Animals↗