Abstract
There are many cold places around the Earth. From the psychrophiles isolated from those environments, cold-adapted enzymes have been isolated. Cold-adapted enzymes have sufficient activity and sufficient substrate-affinity to support the growth, and show low thermo-stability. Artificially cold-adapted enzymes have been obtained by evolutionary engineering from thermophile enzymes. The analysis revealed one of the cold-adaptation mechanisms: the cold-adapted enzymes showed lower enthalpy of substrate-binding thus providing lower activation enthalpy for high activity at low temperature. Some of the cold-adapted enzymes retained high thermal stability of the original thermophile enzyme. The results suggest that it is possible to reconcile high stability with high activity at low temperature. However, the issue needs further investigation. It has been elucidated that life evolved from the hyperthermophilic common ancestor (Commonote). Accordingly, the in vitro evolution experiments for obtaining cold-adapted enzymes from thermophile enzyme are, in a sense, reproducing the evolution of life.
