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Irreversible thermal denaturation of Torpedo californica acetylcholinesterase
Author(s) -
Kreimer David I.,
Shnyrov Valery L.,
Villar Enrique,
Silman Israel,
Weiner Lev
Publication year - 1995
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560041113
Subject(s) - torpedo , differential scanning calorimetry , chemistry , activation energy , denaturation (fissile materials) , kinetics , acetylcholinesterase , reagent , crystallography , kinetic energy , enzyme , thermodynamics , organic chemistry , biochemistry , nuclear chemistry , physics , receptor , acetylcholine receptor , quantum mechanics
Thermal denaturation of Torpedo californica acetylcholinesterase, a disulfide‐linked homodimer with 537 amino acids in each subunit, was studied by differential scanning calorimetry. It displays a single calorimetric peak that is completely irreversible, the shape and temperature maximum depending on the scan rate. Thus, thermal denaturation of acetylcholinesterase is an irreversible process, under kinetic control, which is described well by the two‐state kinetic scheme N → D, with activation energy 131 ± 8 kcal/mol. Analysis of the kinetics of denaturation in the thermal transition temperature range, by monitoring loss of enzymic activity, yields activation energy of 121 ± 20 kcal/mol, similar to the value obtained by differential scanning calorimetry. Thermally denatured acetylcholinesterase displays spectroscopic characteristics typical of a molten globule state, similar to those of partially unfolded enzyme obtained by modification with thiol‐specific reagents. Evidence is presented that the partially unfolded states produced by the two different treatments are thermodynamically favored relative to the native state.