9 - Pancreatic Ribonucleases

Abstract

This chapter reviews recent data on several aspects of the catalytic mechanism of pancreatic RNases as well as some molecular properties such as carbohydrate content and folding and unfolding pathways. This chapter begins with a discussion on reaction catalyzed by pancreatic ribonucleases. The depolymerization of RNA by RNase is described as taking place in two steps: in the first step there is a transphosphorylation reaction from the 5′ position of one nucleotide to the 2′ position of the adjacent nucleotide with the formation of a 2′,3′-cyclic phosphodiester. In the second step, the 2′,3′-cyclic phosphodiester is hydrolyzed to a 3′ nucleotide. The description of this reaction has been a source of ambiguity with respect to the mechanism, especially as to the role of the 2′,3′-cyclic phosphodiesters. This chapter explains concepts related to the specificity of reaction and catalytic mechanism. It also describes structure and functions of substrate-binding subsites. An overview of structure and function of carbohydrate moiety is presented. The chapter concludes with a discussion on folding/unfolding studies of reduced/native RNase A.