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Articles by Y. Yamamoto
Total Records ( 3 ) for Y. Yamamoto
  K Kato , M Yamaguchi Yamada and Y. Yamamoto

Neurochemical and morphological changes in the carotid body are induced by chronic hypoxia, leading to regulation of ventilation. In this study, we examined the time courses of changes in immunohistochemical intensity for tyrosine hydroxylase (TH) and cellular volume of glomus cells in rats exposed to hypoxia (10% O2) for up to 24 hr. Grayscale intensity for TH immunofluorescence was significantly increased in rats exposed to hypoxia for 12, 18, and 24 hr compared with control rats (p<0.05). The transectional area of glomus cells was not significantly different between experimental groups. The TH fluorescence intensity of the glomus cells exhibited a strong negative correlation with the transectional area in control rats (Spearman's = –0.70). This correlation coefficient decreased with exposure time, and it was lowest for the rats exposed to hypoxia for 18 hr ( = –0.18). The histogram of TH fluorescence intensity showed a single peak in control rats. The peaks were gradually shifted to the right and became less pronounced in hypoxia-exposed rats, suggesting that a hypoxia-induced increase in TH immunoreactivity occurred uniformly in glomus cells. In conclusion, this study demonstrates that short-term hypoxia induces an increase in TH protein expression in rat carotid body glomus cells. (J Histochem Cytochem 58:839–846, 2010)

  R.M.C Deshapriya , S Yuhashi , M Usui , T Kageyama and Y. Yamamoto

To identify functionally essential sequences and residues of CTLA-2, in vitro mutagenesis was carried out. The coefficient of inhibition (Ki) was determined towards rabbit cathepsin L using Z-Phe-Arg-MCA as the substrate. Recombinant CTLA-2 inhibited the enzyme potently (Ki = 15 nM). A truncated mutant, lacking the N- and C-terminal Ala1–Asp9 and Leu80–Glu109 regions, was also a potent inhibitor (Ki = 10 nM). Subsequent short deletions in the central region (Asn10–Ser79) showed three functionally essential distinct regions: Asn10–Phe19, His30–Ala44 and Ser55–Ser79. These regions cover sequences corresponding to three helices (1, 2 and 3) and sequences that interact with the cognate enzyme. Alanine scanning showed that replacement of one of three conserved Trp residues increased the Ki by 15–20-fold; whereas, replacement of two/three Trp residues at once caused complete loss of potency, as did replacing Cys75 with Ala or Ser. The proteins from wild-type (WT) CTLA-2 and mutant C75A were stable overnight when incubated with cathepsin L; whereas, proteins from mutants W12A, W15A and W35A were quickly digested. Incubation of cathepsin L/WT CTLA-2 formed a complex; whereas, C75S did not form a complex. Our overall results point to a critical role of W12, W15, W35 and Cys75 residues in CTLA-2.

  T Shibata , S Nagao , H Tai , S Nagatomo , H Hamada , H Yoshikawa , A Suzuki and Y. Yamamoto

Human adult haemoglobin (Hb A), a tetrameric oxygen transfer haemoprotein, has been recognized as an excellent model for investigating the structure–function relationships in allosteric proteins, and has been characterized exhaustively from both experimental and theoretical aspects. Despite the detailed structural and spectroscopic information available for the protein, functional properties have not been as fully elucidated as expected, and hence have remained unexplored. A major drawback for the functional characterization of Hb A is the lack of experimental techniques which enable quantitative characterization of functional properties of the individual subunits of the intact protein. In this study, we have developed techniques for determining the equilibrium constant of the acid–alkaline transition, usually represented as the ‘pKa’ value, in the individual subunits of the met-forms of Hb A (metHb A) and human foetal haemoglobin (metHb F). The pKa values of the individual subunits of metHb A and metHb F have been shown to constitute novel and highly sensitive probes for characterizing the effects of structural changes of not only the interfaces between the subunits within the protein, but also the contact between haem and the protein in the haem pocket. In addition, haem replacement studies of the proteins revealed that the contact between the haem peripheral vinyl side chain and the protein in the haem pocket is important for maintaining the non-equivalence in the haem environment between the subunits of Hb A and Hb F, which could be relevant to the cooperative ligand binding of the proteins.

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