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Biomedical subjects

H Tokunaga

Publications and source records attributed to H Tokunaga.

At least 181 records · Page 10Linked to original sources
PubMed1982

Effects of neurotransmitter candidates on 45Ca uptake by cortical slices of rat brain: stimulatory effect of L-glutamic acid.

The effects of neurotransmitter candidates and the characteristics of the stimulatory effect of L-glutamic acid (L-Glu) on 45Ca uptake by rat brain slices were investigated. 45Ca uptake was significantly stimulated by acetylcholine, serotonin and especially L-Glu, but not by other neurotransmitter candidates. L-Glu caused dose-dependent stimulation of 45Ca uptake (L-Glu-stimulated 45Ca uptake), its effect being half-maximal at 1 microM. The related compounds D-glutamic acid, D,L-alpha-aminoadipic acid and N-methyl-D,L-glutamic acid (final conc. of 10 microM) also stimulated 45Ca uptake, but less than 10 microM L-Glu. D,L-alpha-Methylglutamic acid and L-glutamic acid diethylether (final conc. of 10 microM), which are specific inhibitors of L-Glu, inhibited L-Glu-stimulated 45Ca uptake. Mg,Ca-ATPase activity was hardly affected by a concentration of 10 microM L-Glu that caused maximal stimulation of 45Ca uptake. These findings suggest that L-Glu-stimulated 45Ca uptake by brain cortical slices is linked to L-Glu receptor.

Acetylcholine↗
PubMed1982

Post-translational modification and processing of Escherichia coli prolipoprotein in vitro.

Escherichia coli strain MM18 cells containing malE-lacZ hybrid protein was reported to accumulate prolipoprotein when they were induced with maltose [Ito, K., Bassford, P. J. & Beckwith, J. (1981) Cell 24, 707-717]. We have shown that the prolipoprotein accumulated in maltose-induced MM18 cells is not modified, lacking covalently linked glyceride. When the cell envelope of MM18 containing unmodified prolipoprotein was incubated in the presence of detergent with [2-3H]glycerol-labeled cell envelope of strain JE5505 lacking murein lipoprotein, incorporation of [2-3H]glycerol radioactivity into both prolipoprotein and processed mature lipoprotein was observed. Likewise, when [3H]-palmitate-labeled JE5505 cell envelope was incubated with the MM18 cell envelope containing unmodified prolipoprotein in the presence of detergent, [3H]palmitate radioactivity was incorporated into prolipoprotein by ester linkage and into mature lipoprotein by both ester and amide linkages. These results indicate that our in vitro system contains activities of prolipoprotein modification and processing enzymes, including glyceryltransferase, O-acyltransferase, signal peptidase, and N-acyltransferase. The signal peptidase activity in our in vitro system was completely inhibited by globomycin. At pH 5.0, glyceryltransferase was inactive. Signal peptidase was active at pH 5.0, provided that prolipoprotein had been modified by glyceryltransferase (O-acyl-transferase) during a prior incubation at pH 9.1. These results strongly suggest that the modification of prolipoprotein by glyceryltransferase (and O-acyltransferase) precedes, and may in fact be a prerequisite for, the processing of prolipoprotein by signal peptidase.

Bacterial Proteins↗
PubMed1982

The solute selectivity of porin pores of Escherichia coli and Salmonella typhimurium.

The solute selectivity of porin pores of Escherichia coli and Salmonella typhimurium was examined using vesicle membranes reconstituted from phospholipids and purified porin trimers. OmpE- and 34K-porin-pores allowed a preferential diffusion of phosphorylated and/or negatively charged compounds. They allowed the diffusion of positively charged solutes reasonably well. OmpF- and 35K-porin-pores favored the diffusion of positively charged solutes a little more than negatively charged solutes. OmpC- and 36K-porin-pores showed poor diffusibility to all solute tested. B-porins from E. coli B formed highly efficient pores for the diffusion of both positively and negatively charged solutes. On the basis of these observations, possible mechanisms of solute selectivity were discussed.

Cell Membrane↗
PubMed1981

Permeability properties of chemically modified porin trimers from Escherichia coli B.

The pore-forming protein of the outer membrane of Escherichia coli, porin, was chemically modified with acetic anhydride, succinic anhydride, and glycinamide. Extensive modification of amino groups of the functional porin trimers caused reduced diffusion rates of the negatively charged solutes such as p-nitrophenyl phosphate and AMP, but did not reduce significantly the diffusion of positively charged molecules carbobenzoxy-glycyl-prolyl-arginine-p-nitranilide and tosyl-glycyl-prolyl-arginine-p-nitranilide. Modification of carboxyl groups of trimers caused decreased diffusion rates of the positively charged solutes more significantly than the diffusion rates of negatively charged solutes. The results suggest that the ionic interactions play an important role for the diffusion of charged solutes through the porin pore. The diffusion of p-nitrophenyl alpha-D-glucoside, an uncharged solute, ws not influenced significantly by modification of either amino or carboxyl groups. This observation suggests that modifications only occurred in areas outside of the narrowest portion of the pore or, alternatively, that amino and carboxyl groups are exclusively located at noncylindrical area of the pore. The structural integrity of the acetylated and the succinylated trimers seemed well preserved. On the other hand, modification of carboxyl groups decreased the thermal stability of trimers and extensive modifications caused the dissociation of trimers into monomers at 37 degrees C.

Acetic Anhydrides↗
PubMed1979

Characterization of porins from the outer membrane of Salmonella typhimurium. 1. Chemical analysis.

The three species of channel-forming outer membrane proteins, porins, have been purified to homogeneity from mutant strains of Salmonella typhimurium which produce single species of porin. Purification was by stepwise solubilization with dodecylsulfate or guanidine thiocyanate, gel filtration, and preparative gel electrophoresis. Amino acid compositions and tryptic peptide maps of the three species of porins showed close resemblance, but at the same time clear differences among them. The number of amino acid residues in the porins purified from the strains SH5551, SH6377 and SH6017 were 361, 354 and 345, and their calculated molecular weights 39800, 39300 and 38000, respectively. Amino-terminal and carboxyl-terminal amino acids in all three species of porins appeared to be alanine and phenylalanine, respectively. Neither half-cystine nor hexosamine was found in these preparation of porins. The isoelectric points of porins from the strains SH5551, SH6377 and SH6017, determined by isoelectric focusing, showed slight differences from each other. These results, and the genetic experiments from another laboratory, suggest that the three species of porins in Salmonella typhimurium are distinct polypeptides, probably coded for by distinct structural genes, which might have been derived from the same ancestral gene.

Amino Acids↗
PubMed1979

Characterization of porins from the outer membrane of Salmonella typhimurium. 2. Physical properties of the functional oligomeric aggregates.

We have purified to homogeneity, from mutant strains of Salmonella typhimurium, the small oligomers of porin that confer permeability channels to artificial vesicle membranes reconstituted from phospholipids and lipopolysaccharide. The molecular weights of the porin oligomers from the strains SH5551 and SH6017 appeared to be 130000 and 125000, respectively, and those of the monomers were 41000 and 37500, respectively, when determined by sedimentation equilibrium in the presence of dodecylsulfate. It was thus concluded that the functional porin oligomers consisted of three identical subunits. The Stokes' radius of the trimer . dodecylsulfate complex was around 5 nm. The trimer bound less dodecylsulfate than the monomer. The trimer . dodecylsulfate complex retained at room temperature the native conformation of porin, which is rich in beta-structure. When the trimers were dissociated further by various treatments, only the porin monomers were recovered in significant amounts, and the permeability-conferring activity was lost simultaneously. We propose, therefore, that the trimer is the minimal functional unit of porin that is capable of forming permeability channels in the outer membrane of Salmonella typhimurium.

Cell Membrane↗