Inhibition and Activation of Polynucleotide Phosphorylase by A&dine Orange ++

Preliminary studies by Beers et a2. (1) have shown that the zinc salt of acridine orange can either inhibit or accelerate the rate of polymerization of polynucleotides by polynucleotide phosphorylase of Micrococcus lysodeileticus, depending upon the experimental conditions. We have now confirmed these findings with the zinc-free dye. Some evidence for a reversal of inhibition with degraded ribonucleic acid by a&dine orange has also been obtained (2). Acridine orange forms two classes of complexes with polyribonucleotides. The first complex (Complex I) occurs with the nucleotides along the chain of the polymer and presumably involves both the phosphate and base of each nucleotide unit (3, 4). The second complex (Complex II) apparently involves only the terminal phosphate group of the polymer (1, 5). The binding of the dye by the two kinds of sites of the polymer is influenced by such factors as Mg, ionic strength, and pH (5), all of which also influence the polymerization reaction of catalyzed polynucleotide phosphorylase. In view of the specific nature of these reactions of acridine orange a more detailed study of the effects of the dye on polymerization of polyadenylic acid has been undertaken. It was hoped that a correlation of the effects of Mg, KCl, and polymer on the action of the dye in the enzyme system and on the dye binding properties of polyadenylic acid would give some indication of the site or sites of action of the dye. To a limited extent this objective has been accomplished.