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Biomedical subjects

Y Shibata

Publications and source records attributed to Y Shibata.

At least 721 records · Page 40Linked to original sources
PubMed1981

Cyclic peptides. XI. Synthesis of AM-toxin analogs by intramolecular condensation of pyruvyl-tripeptide amides.

In order to establish possible routes for the synthesis of AM-toxins, cyclotetradepsipeptides containing Dha, Pyr-L-Ala-L-Hmb-L-Tyr-NH2 were prepared and treated with TFA or anhydrous HF. The product was identified to be cyclo (-alpha-Hyala-L-Ala-L-Hmb-L-Tyr-), resulting from intramolecular condensation of the alpha-keto and amide group with the formation of the alpha-Hyala residue. Cyclo (-alpha-Hyala-L-Ala-L-Hmb-L-Phe-) and cyclo (-alpha-Hyala-L-Ala-L-Val-L-Phe-) were obtained by acid-treatment of the corresponding pyruvyl-tripeptide amides. The cyclic tetrapeptides did not show the activity of AM-toxin.

Amides↗
PubMed1981

Effect of tryptophan metabolites and metal ions on the purified kynureninase from rat liver.

Kynureninase purified from rat liver was inhibited by 3-hydroxyanthranilate, or anthranilate, and slightly by 5-hydroxyanthranilate. However, tryptophan metabolites other than anthranilate and its derivatives, and also alpha-keto acids and alanine did not affect the activity of this enzyme. Kynureninase was also inhibited and inactivated by metal ions, especially Hg2+ and Zn2+. On the other hand Mg2+, Ca2+ and monovalent cations had no effect on the activity of the enzyme. The reductants, such as dithiothreitol, reduced glutathione and mercaptoethanol, prevented this inactivation. p-Chloromercurybenzoate (CMB) and N-ethylmaleimide inhibited the enzyme action. Kynureninase which had been completely inactivated by Hg2+ or CMB could be reactivated with excess dithiothreitol, indicating that enzyme inactivation can be attributed to the blocking of sulfhydryl groups. Five sulfhydryl groups per subunit of the enzyme molecule were detected using CMB and mercury orange.

Animals↗
PubMed1980

Purification and properties of kynureninase from rat liver.

Kynureninase [L-kynurenine hydrolase EC 3.7.1.3] has been purified 614-fold from rat liver cytosol. The purification procedure involved pH treatment, ammonium sulfate fractionation, Sephadex G-100 gel filtration, DEAE-Sepharose CL-6B chromatography, extraction with 40% saturated solution of ammonium sulfate and hydroxyapatite chromatography. The enzyme was found to be homogeneous by the criteria of disc gel electrophoresis. SDS-gel electrophoresis and sucrose gradient centrifugation. The enzyme was obtained as a holo-enzyme which showed an absorption maximum at 420 nm. In the absence of pyridoxal 5-phosphate (PLP) the enzyme was dissociated into an apoenzyme. The isoelectric points of holoenzyme and apoenzyme are 5.7 and 6.1. Sucrose gradient centrifugation and SDS-gel electrophoresis gave molecular weight estimates of 95,000 and 55,000, respectively. The optimum pH shifted to higher pH with increase in the concentration of PLP. The Michaelis constants were determined as follows: kynurenine, 240 microM; 3-hydroxykynurenine, 13 microM; PLP, 0.1-1.7 microM. The maximum velocity for 3-hydroxykynurenine was 11 times higher than that for kynurenine at pH 7.7. This enzyme can be regarded as a 3-hydroxykynureninase type enzyme.

Animals↗
PubMed1980

Effect of 4'-chloro-5-methoxy-3-biphenylylacetic acid (DKA-9) on prostaglandin synthetase.

4'-Chloro-5-methoxy-3-biphenylylacetic acid (DKA-9) was evaluated for its ability to inhibit the conversion of arachidonic acid into prostaglandin E2 and the oxygen uptake on arachidonic acid by sheep seminal vesicle microsomes. DKA-9 inhibited equally the formation of prostaglandin E2 and oxygen uptake at 20 mumol/l or more in a concentration-dependent manner, which suggests a blockade of prostaglandin endoperoxide formation. DKA-9 did not promote time-dependent inactivation of the enzyme and inhibited the enzyme competitively with respect to substrate. Thus, it behaved as a reversible and competitive inhibitor.

Animals↗
PubMed1979

Inhibitory effect of cytokinins on PHA-induced human lymphocyte stimulation.

The inhibitory effect of various purine derivatives on PHA-induced human lymphocyte blast formation was studied. Two nucleoside cytokinins, N6-benzyladenosine and N6-isopentenyladenosine, inhibited blast formation at concentrations as low as 10(-6) M. However, the other cytokinins, which lacked the ribosyl residue at N9 position, had to be at the higher molar concentration of 10(-4) before they could induce the same inhibitory effect.

Adenosine↗
PubMed1979

Purification of L-kynurenine 3-hydroxylase by affinity chromatography.

NADP immobilized on agarose is able to adsorb L-kynurenine 3-hydroxylase. The enzyme is released from the adsorbent by passage of a buffer containing 0.5 mM NADP through the column. L-Kynurenine 3-hydroxylase was purified 26-fold with a yield of 12% from mitochondrial outer membrane with a procedure involving DEAE-Sepharose CL-6B, Sephacryl S-200 chromatography and NADP-agarose affinity chromatography. This monooxygenase was a homogeneous protein, giving a monomeric molecular weight of 145,000, which had neither any significant NADPH diaphorase activity nor cytochrome b5-like haem protein. However, the enzyme did not show affinity for a column with L-kynurenine coupled to the gel with a suitable spacer group, and AMP did not serve as an effective ligand in an affinity resin.

Animals↗