Abstract
One purpose of protein engineering is obviously the molecular design of proteins being stable against heat. Thermostability of globular proteins is generally discussed in two different terms; one is the thermodynamic stability and the other is the stability as evaluated from kinetic behaviors of inactivation process. The strict characterization of thermodynamic stability can be made only when the protein denatures reversibly. In contrast the irreversible denaturation of proteins is quantitatively studied in most cases by measuring the rate of thermally induced activity loss at set temperatures. Although these two terms involve the quite different nature, they are sometimes mixed up with each other so that all the discussions are in vain. In this article the protein stability as derived from these two different aspects is compared and the suggestion is made that for further advancement in protein engineering it is essentially important to clarify the reactivity of unfolded proteins yielding aggregation.
