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  • Title: Influence of calcium binding on the thermal stability of 'thermitase', a serine protease from Thermoactinomyces vulgaris.
    Author: Frömmel C, Höhne WE.
    Journal: Biochim Biophys Acta; 1981 Aug 28; 670(1):25-31. PubMed ID: 7023547.
    Abstract:
    'Thermitase' (EC 3.4.21.14), a thermostable extracellular serine protease from Thermoactinomyces vulgaris, binds one calcium ion with a dissociation constant of about 10-4M at 25 degrees C and pH 7.5 to 3.5. In addition, two calcium ions are bound more tightly to the enzyme, as shown by experiments with a calcium-selective electrode. The single most weakly bound calcium ion causes a slight quenching of the protein fluorescence emission, accompanied by a stabilization against thermal denaturation or autolysis and an increase of esterolytic activity of approx. 10%. The tightly bound calcium ions have only a slight influence on activity or on thermal denaturation or autolytic degradation. The activation parameters of thermal denaturation indicate that 'thermitase' belongs to the class of thermostable enzymes with a high intrinsic stability.
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