Protein folding denaturant half-concentration

Enzymes typically function at normal body temperature, 37°C. Their activities at higher temperatures are desirable for rate acceleration, but free enzymes denature at elevated temperatures. Upon intercalation in a-ZrRP (R = OH), both HRP and Hb showed peroxidase activities at over 85°C, observed for the first time, (258) while the free enzyme/protein deactivated rapidly at these temperatures with no activity. The maximum rate of the reaction (Vmax) increased 3.6-fold, while the concentration needed to achieve half the maximum rate (K ) decreased by 20% at these higher temperatures. Such high-temperature activities of enzymes/ proteins are unusual, and they indicate the promise of a-ZrRPs for enzyme stabilization in high-temperature applications. This strategy of enzyme stabilization in a-ZrRP may provide alternatives to thermophilic enzymes obtained from thermo-philes, and these may supplement thermostable enzymes obtained by protein engineering. 

Folded proteins can be caused to spontaneously unfold upon being exposed to chaotropic agents, such as urea or guanidine hydrochloride (Gdn), or to elevated temperature (thermal denaturation). As solution conditions are changed by addition of denaturant, the mole fraction of denatured protein increases from a minimum of zero to a maximum of 1.0 in a characteristic unfolding isotherm (Fig. 7a). From a plot such as Figure 7a one can determine the concentration of denaturant, or the temperature in the case of thermal denaturation, required to achieve half maximal unfolding, ie, where... 

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