title: Tyr-139 in Thermus thermophilus 3-isopropylmalate dehydrogenase is involved in catalytic function.
abstract: The role of Tyr-139, which is thought to be located at the active site of Thermus thermophilus HB8 3-isopropylmalate dehydrogenase, has been investigated by site-specific replacement with phenylalanine. The replacement scarcely affected the Michaelis constant (Km) for 3-isopropylmalate, but caused a 13-fold decrease of that for NAD. The catalytic constant (kcat) showed a 14-fold decrease. Accordingly, the catalytic efficiency (kcat/Km) decreased for 3-isopropylmalate but not for NAD. The results suggest that Tyr-139 is involved in the catalytic function through interaction with 3-isopropylmalate.
authors.affiliation: Department of Life Science, Tokyo Institute of Technology, Yokohama, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Miyazaki
authors.forename: T
authors.initials: T
authors.lastname: Oshima
mesh_terms: D050539:3-Isopropylmalate Dehydrogenase; D000429:Alcohol Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D001483:Base Sequence; D002384:Catalysis; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D016963:Thermus thermophilus / Q000201:enzymology*; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D009838:Oligodeoxyribonucleotides; D014443:Tyrosine; D000429:Alcohol Oxidoreductases; D050539:3-Isopropylmalate Dehydrogenase