title: Role of tryptophan in the active site of plant esterase: chemical modification and fluorometric studies.
abstract: Plant esterase extracted from wheat flour play key roles in the spectrophotometric detection of organophosphorus compounds (OPs) for food safety and human health. The purpose of the present study was to investigate the role of tryptophan residues in the activity and structure of plant esterase by chemical modification and fluorometric studies. Active site characterization of purified plant esterase showed the involvement of tryptophan in the catalytic activity. Only one was essential for the enzyme activity by the Tsou's analysis. Substrate protection experiments further confirmed that the tryptophan residue was located at the substrate-binding site. Fluorescence quenching studies elucidated that the tryptophan residues were largely exposed to the solvent, and a smaller fraction of the surface tryptophan residues had electropositively charged amino acids around them. Experimental results obtained here are expected to promote the applications of plant esterase in OPs detection. Further confirmation of the existence of other critical residues and detailed explanation of their functions were also required for the elucidation of the mechanism involved in the detection of OPs.
authors.affiliation: Center for Bioengineering & Biotechnology, China University of Petroleum (East China), Qingdao 266555, People's Republic of China.
authors.forename: Limin
authors.initials: L
authors.lastname: Yang
authors.forename: Danqun
authors.initials: D
authors.lastname: Huo
authors.forename: Kun
authors.initials: K
authors.lastname: He
authors.forename: Suyi
authors.initials: S
authors.lastname: Zhang
authors.forename: Changjun
authors.initials: C
authors.lastname: Hou
mesh_terms: D020134:Catalytic Domain; D004789:Enzyme Activation; D004950:Esterases / Q000737:chemistry*; D005433:Flour / Q000032:analysis; D005470:Fluorometry / Q000379:methods*; D059022:Food Safety / Q000379:methods; D007211:Indoles / Q000737:chemistry; D009943:Organophosphorus Compounds / Q000032:analysis*; D000078183:Oxindoles; D010940:Plant Proteins / Q000737:chemistry*; D013329:Structure-Activity Relationship; D014908:Triticum / Q000737:chemistry / Q000201:enzymology; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D007211:Indoles; D009943:Organophosphorus Compounds; D000078183:Oxindoles; D010940:Plant Proteins; C022960:2-oxindole; D014364:Tryptophan; D004950:Esterases