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Biomedical subjects

Y Nagai

Publications and source records attributed to Y Nagai.

At least 19 recordsLinked to original sources
PubMed1979

Action of Arthrobacter ureafaciens sialidase on sialoglycolipid substrates. Mode of action and highly specific recognition of the oligosaccharide moiety of ganglioside GM1.

A new bacterial sialidase (N-acetylneuraminate glycohydrolase, EC 3.2.1.18) isolated from the culture filtrate of Arthrobacter ureafaciens was characterized in detail with respect to its action on sialoglycolipids. Strong electrolytes had a reversible inhibitory effect on the action of the enzyme on brain gangliosides in accordance with Debye-Hückel effect of ionic environment on ionic activity, and resulted in an acidic shift and a broadening of the pH optimum. Both ionic and non-ionic detergents markedly enhanced the enzymic activity on the gangliosides, and caused an acidic shift on the pH optimum of this enzyme. Sulfhydryl groups seemed to be involved in its active site. This enzyme had a highly specific action on sialidase-resistant ganglioside GM1, showing about 100-fold higher activity on GM1 than Clostridium perfringens sialidase, the only sialidase so far reported to cleave the lipid substrate in the presence of bile salts. In the absence of detergents, the activity of A. ureafaciens sialidase on GM1 was very low. Ganglioside GM1 in either the monomeric or micelar form was hydrolyzed to asialo-GM1 by A. ureafaciens sialidase most efficiently in the presence of sodium cholate of about three times the GM1 molar concentration. The presence of detergents increased both the Km and Vmax values for ganglioside GM1. The oligosaccharide prepared from GM1 by ozonolysis was cleaved well by this sialidase in the absence of detergents, and no detergent was found to affect the hydrolysis. The Km value for the sugar substrate was about two orders of magnitude greater than that for the corresponding lipid substrate. It is suggested that the hydrophobic ceramide moiety increases affinity of the lipid substrate to the enzyme, but inhibits hydrolysis of the substrate, possibly due to its hydrophobic interaction with hydrophobic portions of the enzyme molecule (resulting in lower Km and Vmax for lipid substrates). This inhibition may be released by detergent due to formation of mixed micelles of sialoglycolipid and detergent molecules. It is also indicated that recognition of the specific saccharide structure of GM1 by individual sialidases is essential for release of the resistant sialyl residue, and that A. ureafaciens sialidase seemed to have an isoenzymic or oligomeric structure.

Arthrobacter↗
PubMed1979

[Thyrotropin-releasing hormone (TRH): action mechanism of an enhanced dopamine release from rat striatal slices (author's transl)].

The enhancing effect of TRH on dopamine(DA) release from rat striatal slices was investigated in relation to Ca2+ and cholinergic mechanisms. TRH(10(-5)--10(-3) M) facilitated concentration dependently the uptake of 14C-DA by rat striatal slices, while methamphetamine (10(-6)--10(-4)M) exhibited a considerable inhibitory effect. TRH (10(-7)--10(--3)M) alone did not increase the DA release into the incubation medium, but it clearly enhanced the DA release in the concomitant presence of desipramine (5 x 10(-5)M). In the superfusion study, TRH (10(-5)--10(-3)M), methamphetamine (10(-6)--10(-4)M) and KCl (2.5--5.0 x 10(-2)M) enhanced the DA release into the perfusion fluid. The DA releasing effect of TRH was completely blocked by cholinergic blockers (scopolamine, hexamethonium and hemicholinium), Ca2+ chelator(EGTA), Ca2+ antagonist(CoCl2) and Ca2+ influx blocker(D-600) or by the removal of Ca2+ from the medium. The methamphetamine-enhanced DA release, however, was not modified by the above treatments except for a partial decline produced by EGTA coupled with the removal of Ca2+. TRH(10(-4)M) also facilitated the uptake of norepinephrine (NE) by rat cerebral cortex slices, but methamphetamine (10-(6)--10(-4)M) exhibited a considerable inhibitory effect. In the superfusion study, TRH (10(-5)--10(-4)M) and methamphetamine (10(-7)--10(-4)M) enhanced the NE release into the perfusion fluid. Therefore, it can be concluded that TRH facilitated the DA release from rat striatal slices by mediating through a cholinergic mechanism and enhancing the influx of Ca2+.

Amino Acids↗
PubMed1979

[Thyrotropin-releasing hormone (TRH): Enhancement of dopamine dependent circling behavior and its own circling-inducing effect in unilateral striatal lesioned animals (author's transl)].

Enhancement by TRH of the dopamine(DA) agonist-induced circling behavior and effect of TRH itself on circling behavior were investigated. TRH(2.5--20 mg/kg, i.p.) remarkably enhanced the circling behavior induced by apomorphine or-L-DOPA in the mice lesioned unilaterally in the caudate nucleus by injection of 6-hydroxydopamine (60OHDA) or by tissue aspiration with subsequent reserpinization. TRH also enhanced the apomorphine-induced stereotypy in reserpinized normal mice. The above TRH-enhancing action of the circling behavior was potentiated, suppressed or unaffected by alpha-methyl-para-tyrosine (alpha-MT) or GABA-ergic drugs. In the 6-OHDA lesioned mice treated with TRH, the cyclic AMP formation by DA or apomorphine was clearly enhanced in the triatal slices taken from the lesioned side but not from the intact side. In the rats lesioned unilaterally in the nigrostriatal DA pathway by 6-OHDA, high doses of TRH injected i.p. (100 mg/kg) or into the non-lesioned caudate nucleus (50 micrograms) produced circling toward the lesioned side, which was suppressed by haloperidol or alpha-MT. TRH(10(-5)--10(-3)M) increased the 14C-DA release from the rat striatal slices in vitro. These results suggest that TRH at low doses facilitates the DA postsynaptic transmission in association with an increase of DA-stimulated cyclic AMP formation in the striatum under supersensitization of the DA receptors, and also at high doses enhances the DA neuronal activity by increasing the DA release from the striatal nerve terminals.

Animals↗
PubMed1979

Isolation and partial characterization of low sulfated chondroitin 4-sulfate-proteoglycan in bovine blood.

Bovine plasma low sulfated chondroitin sulfate-proteoglycan (34 microgram/ml plasma), accounting for the main component of acidic glycosaminoglycans in blood, has been purified by isoelectric precipitation, dissociation with 4 M guanidine chloride followed by DEAE-chromatography, Sephadex G-200 chromatography and by preparative polyacrylamide gel electrophoresis. The proteoglycan, having a molecular weight of approx. 44,000, is composed of about 77% protein and 23% glycosaminoglycan at a molar ratio of 1 : 1 which could be cleaved by alkaline treatment into each component. Amino acid analysis of the proteoglycan and its glycosylpeptide has shown that the material is derived from a different origin from other tissue proteoglycans, though the amino acid residues surrounding O-glycosidic linkage to serine residue are quite similar to that of cartilage proteoglycan. Characteristic features of plasma low sulfate chondroitin sulfate-proteoglycan are discussed, compared with tissue materials.

Amino Acids↗
PubMed1979

Purification of tadpole collagenase and characterization using collagen and synthetic substrates.

Tadpole collagenase hydrolyzed native and denatured collagen and synthetic peptides with sequences of 2,4-dinitrophenyl-L-prolyl-L-leucylglycyl-L-isoleucyl-L-alanylglycyl-L-arginie amide and 2,4-dinitrophenyl-L-prolyl-L-glutaminyl-glycyl-L-isoleucyl-L-alanylglycyl-L-glutaminyl-D-arginine. The specific enzyme activity against the latter substrate and collagen fibrils is found to be 933 nmol/min per mg protein and 8440 units (microgram collagen degraded/min), respectively. Optimum pH for the enzyme is 7.5-8.5. A collagenase complex with alpha2-macroglobulin did not hydrolyze collagen fibrils, but digested the synthetic substrates at the Gly-Ile bond. The amino acid composition of the enzyme was determined. Immunoelectrophoresis of the enzyme at pH 8.6 against anti-tadpole collagenase rabbit immunoglobulin G shows a single precipitin line at a position migrating faster than human serum albumin and corresponding to enzyme activity against collagen fibril and synthetic substrates.

Amino Acid Sequence↗
PubMed1979

In vitro studies of gonadal organogenesis in the presence and absence of H-Y antigen.

In a very strict sense, the primary (gonadal) sex of mammals is determined not so much by the presence or absence of the Y but the expression or nonexpression of the evolutionary extremely conserved plasma membrane H-Y antigen. The central somatic blastema of embryonic indifferent gonads contains one cell lineage characterized by the possession of S-F differentiation antigen that differentiates into testicular Sertoli cells in the presence of H-Y and into ovarian follicular (granulosa) cells in its absence. This cell lineage appears to play the most critical role in gonadal differentiation. Whether or not testicular Leydig cells and ovarian theca cells are similarly derived from the common cell lineage has not been determined. Nevertheless, if given H-Y antigen, presumptive theca-cell precursors of the fetal ovary acquire hCG (LH?)-receptors-the characteristic of fetal Leydig cells.

Animals↗
PubMed1979

Synthesis of 2,3,4,4a,5,9b-hexahydro-1H-pyrido[4,3-b]indole derivatives and their central nervous system activities.

The synthesis and some pharmacological effects of cis- and trans-2-substituted 2,3,4,4a,5,9b-hexahydro-1H-pyrido[4,3-b]indole derivatives are described. In these derivatives, the substituents of the 2, 5 and 8 position, together with the relative configuration of the 4a and 9b position, influenced the potency of the central nervous system activities. A cis-2-[3-(p-fluorobenzoyl)propyl] analogue (5k) of carbidine (1) possessed not only thymoleptic-like biological activity but had more potent neuroleptic activity than the parent drug.

Animals↗
PubMed1979

Separation of the alpha chains of type I and III collagens by SDS-polyacrylamide gel electrophoresis.

A method for the separation of type III collagen from type I collagen by SDS-polyacrylamide gel electrophoresis has been developed. This is based on the observation that the presence of 3-4 M urea decreases the mobility of the alpha 1 [III] chain to a greater extent than those of the alpha 1[I] and alpha 2 chains, although the alpha 1[I] and alpha 1[III] chains move at the same rate in the absence of urea. An attempt to separate the alpha 1[II] chain of type II collagen from the alpha 1[I] chain was unsuccessful under the experimental conditions employed.

Animals↗
PubMed1979

The spread of a pathogenic and an apathogenic strain of Newcastle disease virus in the chick embryo as depending on the protease sensitivity of the virus glycoproteins.

The pathogenic strain Italien and the apathogenic strain Ulster of Newcastle disease virus have been compared with respect to organ tropism and spread of infection in 11-day-old chick embryos. After infection of the endodermal layer of the chorioallantoic membrane by intra-allantoic inoculation with strain Italien, high virus titres are found in all extra-embryonic membranes and fluids and in the embryo itself. Infection results in early death of the embryo. In contrast, after infection with strain Ulster by the same route of inoculation, high virus titres are found only in the allantoic sac and embryos are not killed. Inoculations with strain Italien on to the ectodermal layer through an artificial air sac results in rapid spread of infection in the chorioallantoic membrane and the embryo dies before the virus invades other tissues including the embryo. Under the same conditions of infection, strain Ulster neither spreads within chorioallantoic membrane nor does it kill the embryo. Virus spread in each germinal layer of the chorioallantoic membrane was analysed by immune fluorescence. These studies showed that endoderm as well as mesoderm and ectoderm allowed the spread of strain Italien, whereas only the endoderm is permissive for strain Ulster. These differences in host range are based upon differential activation of the virus glycoproteins by proteolytic cleavage. The glycoproteins of strain Italien are cleaved in each germinal layer, whereas those of strain Ulster are cleaved only in endoderm. These studies demonstrate that, in the system analysed here, spread of infection and organ tropism are important factors for pathogenicity and both of these factors are determined by the susceptibility of the virus glycoproteins to proteolytic cleavage.

Allantois↗
PubMed1979

Isolation and characterization of heat-resistant (HR) mutants of Newcastle disease virus.

Heat-resistant (HR) mutants (MR 70 and HR 74) of Newcastle disease virus (NDV) which exhibited significantly higher thermostability in their infectivity than wild-type virus were isolated and characterized. They differ from each other in their plaque morphology; HR 70 produces small turbid plaques, whereas those of HR 74 are large and clear. Cytopathogenicity of these mutants is much lower than that of the wild-type virus in cultured cells such as CEF, LLCMK2 and HeLa cells. Moreover, these HR mutants exhibited extended mean embryo survival times. Synthesis of cellular RNA's and proteins in cells infected with HR mutants was not significantly reduced under conditions in which synthesis of these macromolecules was strongly reduced in cells infected with wild-type virus. No significant differences were observed between HR mutants and wild-type virus in their other phenotypic characteristics such as the capacity for interferon production, growth characteristics at a low multiplicity of infection, and cleavage of viral glycoproteins in infected cells. From these findings, it was suggested that the inhibitory effect of virus infection on cellular macromolecular synthesis is a possible determinant of cytopathogenicity of NDV.

Animals↗