title: Monitoring the kinetics and thermodynamics of interfacial enzymatic catalysis by differential scanning calorimetry.
abstract: Using phase transition profile as an indicator of thermodynamic property and phase transition heat as the second indicator of the percentage of substrates unhydrolyzed, differential scanning calorimetry has been used to observe in detail the kinetics and thermodynamics of phospholipase A(2)-catalyzed 1,2-dipalmitoyl-sn-glycero-3-phosphocholine large unilamellar vesicle (LUV) hydrolysis. Phase transition profiles show that the original LUV almost completely changes into a novel aggregate at the end of the latency, followed by an abrupt activation of the reaction. The phase transition profiles are asymmetric between the heating and cooling curves, indicating a thermodynamic mesostatic property of the system. The reaction in activated phase follows a single first-order kinetics and all of the substrates in vesicles can be hydrolyzed. All these evidences indicate that the products and substrates can freely exchange between the outer and the inner layers of the vesicles and the membrane of the vesicle in the activated phase is permeable. This permeability favors the exchange of the substrates and products, thus, resulting in the activation of the fast reaction.
authors.affiliation: Institute of Physical Chemistry, College of Chemistry and Molecular Engineering, State Key Laboratory for Structural Chemistry of Stable and Unstable Species, Peking University, Beijing 100871, China.
authors.forename: Lifeng
authors.initials: L
authors.lastname: Cai
authors.forename: Aoneng
authors.initials: A
authors.lastname: Cao
authors.forename: Luhua
authors.initials: L
authors.lastname: Lai
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine; D002021:Buffers; D002152:Calorimetry, Differential Scanning / Q000379:methods; D004798:Enzymes / Q000737:chemistry* / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D008081:Liposomes; D010741:Phospholipases A / Q000737:chemistry* / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D002021:Buffers; D004798:Enzymes; D008081:Liposomes; D015060:1,2-Dipalmitoylphosphatidylcholine; D010741:Phospholipases A