title: The effect of citric acid on the activity, thermodynamics and conformation of mushroom polyphenoloxidase.
abstract: Few reports have focused on the effect of citric acid on thermodynamics and conformation of polyphenoloxidase (PPO). In this study, variations on activity, thermodynamics and conformation of mushroom PPO induced by citric acid (1-60mM) and relationships among these were investigated. It showed that with the increasing concentration of citric acid, the activity of PPO decreased gradually to an inactivity condition; inactivation rate constant (k) of PPO increased and the activation energy (Ea) as well as thermodynamic parameters (ΔG, ΔH, ΔS) decreased, which indicated that the thermosensitivity, stability and number of non-covalent bonds of PPO decreased. The conformation was gradually unfolded, which was reflected in the decrease of α-helix contents, increase of β-sheet and exposure of aromatic amino acid residuals. Moreover, two linear relationships of relative activities, enthalpies (ΔH) against α-helix contents were obtained. It indicated that changes of activity and thermodynamics might correlate to the unfolding of conformation.
authors.affiliation: State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, Jiangxi, China. liuwei@ncu.edu.cn
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.forename: Li-qiang
authors.initials: LQ
authors.lastname: Zou
authors.forename: Jun-ping
authors.initials: JP
authors.lastname: Liu
authors.forename: Zhao-qin
authors.initials: ZQ
authors.lastname: Zhang
authors.forename: Cheng-mei
authors.initials: CM
authors.lastname: Liu
authors.forename: Rui-hong
authors.initials: RH
authors.lastname: Liang
mesh_terms: D000363:Agaricales / Q000737:chemistry / Q000201:enzymology*; D004156:Catechol Oxidase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D019343:Citric Acid / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004795:Enzyme Stability / Q000187:drug effects; D005656:Fungal Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D017510:Protein Folding / Q000187:drug effects; D017433:Protein Structure, Secondary / Q000187:drug effects; D058767:Protein Unfolding / Q000187:drug effects; D013816:Thermodynamics
chemical_list: D004791:Enzyme Inhibitors; D005656:Fungal Proteins; D019343:Citric Acid; D004156:Catechol Oxidase