New pyrimidine (uridine) specific cyclizing 2'-ribonucleotidyltransferase and nonspecific decyclizing 2',3'-phosphodiesterase

Abstract

Chromatography of an aqueous extract of rape seedlings on modified Cellex P, followed by chromatography on two types of modified Sepharose 4B, afforded two nucleolytic activities which split ribonucleoside 2',3'-cyclic phosphates. The first enzyme (C1) affording 2'-nucleotides on splitting, was characterized as a decyclizing 2',3'-phosphodiesterase, nonspecific towards the nature of the heterocyclic base. The second enzyme (D2) splits uridine 2',3'-cyclic phosphate and cytidine 2',3'-cyclic phosphate with high preference for the uridine derivative, its specificity towards the heterocyclic base and the sugar moiety resembling that of pancreatic ribonuclease. The products are in both cases 3'-ribonucleotides. The enzyme splits also alkyl esters of uridine 3'-phosphate with the intermediary formation of uridine 2',3'-cyclic phosphate. The splitting rate decreases with growing alkyl moiety. This enzyme is classified as a new pyrimidine specific cyclizing 2-ribonucleotidyltransferase (EC 2.7.7). Both enzymes were isolated free of other nucleolytic activities. In the native state they are stabilized by an acidic protein.