title: Interaction of monosulfonate tetraphenyl porphyrin (H2TPPS1) with plant-esterase: determination of the binding mechanism by spectroscopic methods.
abstract: The interaction of monosulfonate tetraphenyl porphyrin (H(2)TPPS(1)) with plant-esterase was investigated using fluorescence and UV-vis absorption spectroscopy. Fluorescence quenching, from which the binding parameters were evaluated, revealed that the quenching of the esterase by H(2)TPPS(1) resulted from the formation of a dye-esterase complex. According to the modified Stern-Volmer equation, the effective quenching constants (K(a)) between H(2)TPPS(1) and plant-esterase at four different temperatures (297 K, 300 K, 303 K, and 306 K) were obtained to be 14.132×10(5), 5.734×10(5), 2.907×10(5), and 2.291×10(5) M(-1), respectively. The thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS) for the reaction were calculated to be -181.67 kJ M(-1) and -0.49 kJ M(-1)K(-1), indicating that van der Waals force and hydrogen bonds were the dominant intermolecular force in stabilizing the complex. Site marker competitive experiments showed that the binding of H(2)TPPS(1) to plant-esterase primarily took place in the active site. The binding distance (r) was obtained to be 5.99 nm according to Förster theory of non-radioactive energy transfer. The conformation of plant-esterase was investigated by synchronous fluorescence and UV-vis absorption spectroscopy, and the results confirmed some micro-environmental and conformational changes of plant-esterase molecules.
authors.affiliation: College of Bioengineering/Key Laboratory of Biorheology Science and Technology of Ministry of Education, Chongqing University, Chongqing, PR China.
authors.forename: Limin
authors.initials: L
authors.lastname: Yang
authors.forename: Danqun
authors.initials: D
authors.lastname: Huo
authors.forename: Changjun
authors.initials: C
authors.lastname: Hou
authors.forename: Mei
authors.initials: M
authors.lastname: Yang
authors.forename: Huanbao
authors.initials: H
authors.lastname: Fa
authors.forename: Xiaogang
authors.initials: X
authors.lastname: Luo
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D004735:Energy Transfer; D004950:Esterases / Q000737:chemistry / Q000378:metabolism*; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010944:Plants / Q000201:enzymology*; D011166:Porphyrins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
chemical_list: D011166:Porphyrins; C016136:tetraphenylporphine sulfonate; D004950:Esterases