The Structure and Function of Ribonuclease T1

Abstract

Ribonuclease T₁ [EC 3.1.4.8] was coupled to a water-insoluble cross-linked polyacrylamide (Enzacryl AH) by the acid azide method. The immobilized enzyme exhibited about 45% and 77% of the original activity toward yeast RNA and 2′, 3-cyclic GMP, respectively, as substrates. Although the specific activity was lowered by the coupling, the immobilized enzyme was found to be far more stable to heat and extremes of pH than the native enzyme. The immobilized enzyme was active toward RNA even above pH 9 (at 37^˚C) or above 60^˚C (at pH 7.5), where the native enzyme was inactive. The immobilized enzyme retained much of its activity as assayed at 37^˚C after incubation in the range of pH 1 to 10 at 37^˚C, or after heating at 100^˚C (at pH 7.5) under conditions where the native enzyme was inactivated to a considerable extent. The enzyme derivative could be repeatedly recovered and reused without much loss of activity. The active site glutamic acid-58 in the immobilized enzyme appeared to be nearly as reactive with iodoacetate as that in the native enzyme.