Studies on the inactivation of whale pancreatic ribonuclease W 1 with iodoacetate

Abstract

The influence of iodoacetate on the whale pancreatic ribonuclease (ribonuclease W 1) (EC 2.7.7.16) was studied. The inactivation of ribonuclease W 1 by action of iodoacetate occurred most rapidly at pH 5.0–5.7. The presence of 3 molar equivalents of uridine 2′(3′)-phosphate and cytidine 2′(3′)-phosphate to ribonuclease W 1, largely inhibited the inactivation, but the inhibition was very slight when purine nucleoside 2′(3′)-phosphates instead of pyrimidine nucleoside 2′(3′)-phosphate were present. The products of the reaction of iodoacetate with ribonuclease W 1 at pH 5.0 were separated by column chromatography using SE-Sephadex. The main product seemed to be a modified ribonuclease W 1, which was produced by introduction of one mole of carboxymethyl group per one mole of the protein. The products obtained by the similar reaction performed at pH 8.5 were separated into at least nine peaks of the fractions, among which only one peak had no enzymatic activity.