Organismal adaptation to extreme temperatures yields enzymes with distinct configurational stabilities, including thermophilic and psychrophilic enzymes, which are adapted to high and low temperatures, respectively. These enzymes are widely assumed to also have unique rate-temperature dependencies. Thermophilic enzymes, for example, are considered optimal at high temperatures and effectively inactive at low temperatures due to excess rigidity. Surveying published data, we find that thermophilic, mesophilic, and psychrophilic enzymes exhibit indistinguishable rate-temperature dependencies. Furthermore, given the nonenzymatic rate-temperature dependency, all enzymes, regardless of their operation temperatures, become >10-fold less powerful catalysts per 25°C temperature increase. Among other factors, this loss of rate acceleration may be ascribed to thermally induced vibrations compromising the active-site catalytic configuration, suggesting that many enzymes are in fact insufficiently rigid.
Bibliographical noteFunding Information:
This work was inspired by review comments to  and illuminating discussions with Brian Shoichet. We are also grateful to Ron Milo, Arren Bar-Even, James Fraser, Nobuhiko Tokuriki, and Arieh Warshel for inspiring discussions and valuable comments. Financial support by the Israel Science Foundation is gratefully acknowledged.
Copyright 2014 Elsevier B.V., All rights reserved.
- Active-site preorganization
- Enzyme dynamics
- Rate temperature-dependency
- Thermal vibrations
- Thermophilic enzymes