title: Kinetic parameters and recognition of thymidine analogues with varying functional groups by thymidine phosphorylase.
abstract: Thymidine phosphorylase (TP, EC 2.4.2.4) recognized the structure of the substrate with high specificity, via both the base and the ribosyl moieties. The replacement of 3'-OH of thymidine markedly influenced its catalytic activity with TP. The conversion of pyrimidine nucleosides with modified base moieties to the corresponding 1-phosphate form was poor. The leaving group activity decreased with an increase in aromaticity of the pyrimidine base moiety, because of increased difficulty in polarizing the base by the amino acids local to the active site. The replacement of 3' and 5' functional groups tended to decrease the reaction rate and the percentage conversion with TP. In particular the ribosyl 3' hydroxyl group was structurally important for the binding of the substrate by the enzyme. The kinetic assay clearly showed high K(m) and low V(max) values on replacing the 3' hydroxyl group with hydrogen.
authors.affiliation: Department of Materials and Life Science, Shizuoka Institute of Science and Technology, 2200-2 Toyosawa, Fukuroi, Shizuoka 437-8555, Japan. a-hatano@ms.sist.ac.jp
authors.forename: Akihiko
authors.initials: A
authors.lastname: Hatano
authors.forename: Aiko
authors.initials: A
authors.lastname: Harano
authors.forename: Yoshikatsu
authors.initials: Y
authors.lastname: Takigawa
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Naramoto
authors.forename: Keisuke
authors.initials: K
authors.lastname: Toda
authors.forename: Yuuichi
authors.initials: Y
authors.lastname: Nakagomi
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Yamada
mesh_terms: D007700:Kinetics; D015394:Molecular Structure; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D013936:Thymidine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism*; D013939:Thymidine Phosphorylase / Q000378:metabolism*
chemical_list: D013939:Thymidine Phosphorylase; D013936:Thymidine