Why Are Thermophilic Enzymes Poorly Active at Low Temperature

A second factor to consider is the intrinsic increase in reaction rates caused by increasing temperature. An enzyme maintaining a rapid rate at low temperatures will exhibit extremely rapid reaction rates at elevated temperatures. Enzymes must function within the context of cellular metabolism, and such ultrafast enzymes may be disadvantageous. 

To date, only a small number of directed evolution studies of temperature adaptation have been carried out. From this small data set we can nonetheless draw several interesting conclusions. 

Directed evolution as a tool to probe the basis of protein structure, stability, and function is in its infancy, and many fruitful avenues of research remain to be explored. Studies so far have focused on proteins that unfold irreversibly, making detailed thermodynamic analysis impossible. The application of these methods to reversibly folding proteins could provide a wealth of information on the thermodynamic basis of high temperature stability. A small number of studies on natural thermophilic proteins have identified various thermodynamic strategies for stabilization. Laboratory evolution makes it possible to ask, for example, whether proteins have adopted these different strategies by chance, or whether certain protein architectures favor specific thermodynamic mechanisms. It will also be possible to determine how other selective pressures, such as the requirement for efficient low temperature activity, influence stabilization mechanisms. The combination of directed evolu- 

Arnold, F. H., and Wintrode, P. L. (1999). In Encyclopedia of Bioprocess Technology Fermentation, Biocatalysis, and Bioseperation (Flickinger, M. C., and Drew, S. W. eds.), pp. 971-987. John Wiley Sons, New York. 

Auerbach, G., Huber, R., Grattinger, M., Zaiss, K., Schurig, H., andjaenicke, R. (1997a). Structure 5, 1475—1483. 

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