Irreversible thermal denaturation of Torpedo californica acetylcholinesterase

• Published in: Protein science Vol. 4; no. 11; pp. 2349 - 2357
• Main Authors: Kreimer, David I., Shnyrov, Valery L., Villar, Enrique, Silman, Israel, Weiner, Lev
• Format: Journal Article
• Language: English
• Published: Bristol Cold Spring Harbor Laboratory Press 01.11.1995
• Subjects: acetylcholinesterase; Acetylcholinesterase - chemistry; Animals; Calorimetry, Differential Scanning; differential scanning calorimetry; Disulfides - chemistry; Electrophoresis, Polyacrylamide Gel; Guanidine; Guanidines; Hot Temperature; irreversible denaturation; Kinetics; molten globule; Protein Denaturation; Spectrometry, Fluorescence; Sulfhydryl Compounds - chemistry; Thermodynamics; thiol‐disulfide exchange; Torpedo; two‐state kinetic model
• ISSN: 0961-8368; 1469-896X
• DOI: 10.1002/pro.5560041113

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.