HIGHLY STABLE CA2-DEPENDENT DNASE FROM CRAB HEPATOPANCREAS(,MG2+)

The stability of Ca2+,Mg2+-dependent DNase from the hepatopancreas of the king crab Paralithodes camtschatica to various denaturing factors has been studied. The DNase is thermostable, its inactivation half-tim e at 100 degrees C being 10 min and its temperature optimum 70 degrees C. The enzyme is stable in neutral and alkaline media but is inactiva ted at pH < 6.0. The enzyme is resistant to some denaturing reagents. The DNase activity decreases twofold in the presence of 1 M urea, 30% ethanol, 0.5% sodium deoxycholate or Triton X-100, or 0.1% sodium dode cyl sulfate. Dithiothreitol and 2-mercaptoethanol at 0.8% do not marke dly influence its activity. The protein contains 36 half-cystine resid ues by Ellman's method. The absence of free sulfhydryl groups indicate s that there are 18 disulfide bonds in the native enzyme. The amino ac id composition of the enzyme was determined.