title: Influence of calcium binding on the thermal stability of 'thermitase', a serine protease from Thermoactinomyces vulgaris.
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.
mesh_terms: D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D004355:Drug Stability; D010450:Endopeptidases / Q000378:metabolism*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008848:Micromonosporaceae / Q000201:enzymology*; D011485:Protein Binding; D011489:Protein Denaturation; D012697:Serine Endopeptidases; D013050:Spectrometry, Fluorescence
chemical_list: D010450:Endopeptidases; D012697:Serine Endopeptidases; C022728:thermitase; D002118:Calcium