Deoxyadenosine Diphosphate as a Substrate and Inhibitor of Polynucleotide Phosphorylase of Micrococcus luteus: I. DEOXYADENOSINE DIPHOSPHATE AS A SUBSTRATE FOR POLYMERIZATION AND THE EXCHANGE REACTION WITH INORGANIC 32P

Abstract

Abstract Polynucleotide phosphorylase of Micrococcus luteus catalyzes the addition of a single dAMP moiety from dADP onto an oligoribonucleotide. Further addition of either dAMP or AMP residues to the resulting (Ap)ndA is very difficult. The chain elongation reaction proceeds faster in the presence of Mn2+ than in the presence of Mg2+. The enzyme also catalyzes an exchange between the β-phosphate of dADP and 32Pi, but only in the presence of either an oligoribonucleotide bearing an unesterified C-3'-hydroxyl group or of ADP. Similar results are obtained with Form I (primer-independent) and Form T (primer-dependent) enzyme. It appears that 32Pi-dADP exchange occurs by the addition of a dAMP residue to the end of a polyribonucleotide (or oligoribonucleotide) chain and the subsequent phosphorolysis of the internucleotide bond. Furthermore, no evidence for the formation of a dAMP-enzyme complex could be obtained. Incubation of the enzyme with dADP as the sole substrate results, rather, in the formation of a limited amount of (dA)n. This reaction also proceeds more readily in the presence of Mn2+ than in Mg2+.