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Articles by T Matsuoka
Total Records ( 2 ) for T Matsuoka
  M Imada , K Masuda , R Satoh , Y Ito , Y Goto , T Matsuoka , S Endo , A Nakamura , H Kawamoto and T. Takai

Activated mature T cells induce various inhibitory receptors implicated in maintaining peripheral tolerance in response to the trans-acting ligands. Interestingly, paired Ig-like receptor (PIR)-B, an inhibitory MHC class I receptor on B cells and myeloid cells, could be involved in regulating early T cell development because epitope for PIR is detected on pre-thymic T/NK progenitors but not on thymocytes or mature T cells. We hypothesized that PIR-B is not only a regulator for T cell development but is also detrimental if expressed on mature T cells. Here we demonstrated, using PIR-B-deficient fetuses, that PIR-B is indeed expressed on the T cell progenitors but failed to identify its distinctive roles in the development. Forced expression of PIR-B in thymocytes and mature T cells also resulted in no abnormalities in development. However, upon antigenic or allogeneic stimulation, peripheral T cells with the ectopic PIR-B showed reduced Th type 1 responses due to the suppression of proximal TCR signaling by constitutive binding of PIR-B to MHC class I on the same cell surface. Our findings suggest that T cell expression of PIR-B with the cis-interacting MHC class I is strictly prohibited in periphery so as to secure prompt immune responses.

  H Tamaki , T Matsuoka , Y Yasuda , S Hanada , Y Kamagata , K Nakamura and S. i. Sakasegawa

A unique urate-oxidizing enzyme was identified in a bacterium, strain T-15. Based on its phylogenetic, physiological and biochemical properties, strain T-15 was deemed to be a novel species within the genus Lysobacter. The enzyme expressed in Lysobacter sp. T-15 was composed of 592 amino acids and contained four consensus copper-binding sites, and the recombinant enzyme was, at least in this study, speculated to have three Cu ions per subunit. The primary structure of the enzyme was 33% identical to Marinomonas mediterranea polyphenol oxidase, but it showed no significant similarity to any known urate oxidase. With urate as the substrate, the catalytic efficiency (kcat/Km) of recombinant enzyme was 4.0 x 102 s1mM1, and it was not inhibited by xanthine, a strong urate oxidase inhibitor. The enzyme also showed activity toward 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid), 2,6-dimethoxyphenol and bilirubin, with catalytic efficiencies of 4.9 x 102, 1.1 x 102 and 3.6 x 103 s1mM1, respectively. We deemed the enzyme would be a member of laccase from its broad substrate specificity. However, typical laccase and other multi-copper oxidases such as bilirubin oxidase and ascorbate oxidase seldom exhibit urate oxidation activity. These results would expand the laccase substrate range to include urate.

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