title: The sole cysteine residue (Cys301) of tetrathionate hydrolase from Acidithiobacillus ferrooxidans does not play a role in enzyme activity.
abstract: Cysteine residues are absolutely indispensable for the reactions of almost all enzymes involved in the dissimilatory oxidation pathways of reduced inorganic sulfur compounds. Tetrathionate hydrolase from the acidophilic iron- and sulfur-oxidizing bacterium Acidithiobacillus ferrooxidans (Af-Tth) catalyzes tetrathionate hydrolysis to generate elemental sulfur, thiosulfate, and sulfate. Af-Tth is a key enzyme in the dissimilatory sulfur oxidation pathway in this bacterium. Only one cysteine residue (Cys301) has been identified in the deduced amino acid sequence of the Af-Tth gene. In order to clarify the role of the sole cysteine residue, a site-specific mutant enzyme (C301A) was generated. No difference was observed in the retention volumes of the wild-type and mutant Af-Tth enzymes by gel-filtration column chromatography, and surprisingly the enzyme activities measured in the cysteine-deficient and wild-type enzymes were the same. These results suggest that the sole cysteine residue (Cys301) in Af-Tth is involved in neither the tetrathionate hydrolysis reaction nor the subunit assembly. Af-Tth may thus have a novel cysteine-independent reaction mechanism.
authors.affiliation: a Department of Biofunctional Chemistry, Division of Agricultural and Life Science, Graduate School of Environmental and Life Science , Okayama University , Okayama , Japan.
authors.forename: Tadayoshi
authors.initials: T
authors.lastname: Kanao
authors.forename: Hisayuki
authors.initials: H
authors.lastname: Nakayama
authors.forename: Mizuki
authors.initials: M
authors.lastname: Kato
authors.forename: Kazuo
authors.initials: K
authors.lastname: Kamimura
mesh_terms: D042763:Acidithiobacillus / Q000201:enzymology* / Q000235:genetics; D000409:Alanine / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism*; D057075:Enzyme Assays; D015870:Gene Expression; D006867:Hydrolases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010084:Oxidation-Reduction; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D006867:Hydrolases; C104756:tetrathionate hydrolase; D003545:Cysteine; D000409:Alanine
keywords: Acidithiobacillus ferrooxidans; cysteine residue; sulfur metabolism; tetrathionate hydrolase