Studies on 3′-Nucleotidase-nuclease from Potato Tubers

Hydrolysis of 2′(3′)-AMP and 2′(3′), 5′-ADP by potato 3′-nucleotidase-nuclease was studied in detail and the specific attack on nucleoside 3′-phosphates was confirmed. 2. Poly A was degraded principally to 5′-AMP by this enzyme. 3. A time course study of hydrolysis of RNA indicated the endonucleolytic nature of the nuclease. 4. Adenosine 3′-benzylphosphate was hydrolyzed to adenosine and benzylphosphate by this enzyme, while adenosine 5′-benzylphosphate was not a substrate. 5. It is concluded from those findings that the enzyme can recognize nucleoside 3′-phosphate moiety (monoester and diester) as the substrate and cleaves the 3′ O-P bond. 6. The kinetic parameters, Km and Vmax, of 3′-nucleotidase-nuclease for 3′-ribonucleotides were determined. Ribonucleosides and 5′-ribonucleotides were competitive inhibitors of this enzyme and their K1 values were determined. RNA and also poly A were potent competitive inhibitors of this enzyme. 7. On the basis of these data, it seemed reasonable to assume that the potato 3′-nucleotidase-nuclease has an active site which includes a nucleoside-binding site and two phosphate-binding sites.