Psychrophilic enzymes: revisiting the thermodynamic parameters of activation may explain local flexibility.
Basic theoretical and practical aspects of activation parameters are briefly reviewed in the context of cold-adaptation. In order to reduce the error impact inherent to the transition state theory on the absolute values of the free energy (DeltaG(#)), enthalpy (DeltaH(#)) and entropy (DeltaS(#)) of activation, it is proposed to compare the variation of these parameters between psychrophilic and mesophilic enzymes, namely Delta(DeltaG(#))(p-m), Delta(DeltaH(#))(p-m) and Delta(DeltaS(#))(p-m). Calculation of these parameters from the available literature shows that the main adaptation of psychrophilic enzymes lies in a significant decrease of DeltaH(#), therefore leading to a higher k(cat), especially at low temperatures. Moreover, in all cases including cold-blooded animals, DeltaS(#) exerts an opposite and negative effect on the gain in k(cat). It is argued that the magnitude of this counter-effect of DeltaS(#) can be reduced by keeping some stable domains, while increasing the flexibility of the structures required to improve catalysis at low temperature, as demonstrated in several cold-active enzymes. This enthalpic-entropic balance provides a new approach explaining the two types of conformational stability detected by recent microcalorimetric experiments on psychrophilic enzymes.
Lonhienne
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T
Laboratory of Biochemistry, Institute of Chemistry B6, University of Liège, B-4000, Liège, Belgium.
Gerday
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C
Feller
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G
D000064:Acclimatization; D000818:Animals; D000864:Antarctic Regions; D001407:Bacillus; D003080:Cold Temperature; D004789:Enzyme Activation; D004795:Enzyme Stability; D004798:Enzymes / Q000737:chemistry*; D005399:Fishes; D010735:Phosphoglycerate Kinase / Q000737:chemistry; D011487:Protein Conformation; D017510:Protein Folding; D011549:Pseudomonas; D013816:Thermodynamics; D000516:alpha-Amylases / Q000737:chemistry
D004798:Enzymes; D010735:Phosphoglycerate Kinase; D000516:alpha-Amylases