Metalloprotease from Bacillus thuringiensis

摘要

Bacillus thuringiensis var. kurstaki was shown to produce an extracellular, metal chelator-sensitive protease during the early stages of sporulation. Protease production in nutrient broth was dependent upon supplementation with Mn2+ or Ca2+. The addition of Ca2+ was required for enzyme stabilization. Protease production occurred in nutrient broth supplemented with 7 × 10-3 M Ca2+, 5 × 10-4 M Mn2+, and 10-3 M Mg2+. The protease had optimum activity in the pH range 6.5 to 7.5. It was inhibited by chelating agents but not by a serine protease inhibitor. The culture supernatant and the partially purified protease lacked esterase activity. Partial purification of the enzyme (92.3 ×) by (NH4)2SO4 fractionation and starch adsorption yielded an enzyme whose molecular weight was estimated to be 37,500 by acrylamide gel-sodium dodecyl sulfate electrophoresis or 40,800 by sucrose density gradient centrifugation. In the presence of Ca2+, the partially purified enzyme retained 78% of its activity after heating at 70 C for 10 min but only 8% of its activity after heating at 80 C for 10 min.