Polyphosphates strongly inhibit the tRNA dependent synthesis of poly(A) catalyzed by poly(A) polymerase from Saccharomyces cerevisiae

Polyphosphates of different chain lengths (P 3, P 4, P 15, P 35), (1 μM) inhibited 10, 60, 90 and 100%, respectively, the primer (tRNA) dependent synthesis of poly(A) catalyzed poly(A) polymerase from Saccharomyces cerevisiae. The relative inhibition evoked by p 4A and P 4 (1 μM) was 40 and 60%, respectively, whereas 1 μM Ap 4A was not inhibitory. P 4 and P 15 were assayed as inhibitors of the enzyme in the presence of (a) saturating tRNA and variable concentrations of ATP and (b) saturating ATP and variable concentrations of tRNA. In (a), P 4 and P 15 behaved as competitive inhibitors, with K i values of 0.5 μM and 0.2 μM, respectively. In addition, P 4 (at 1 μM) and P 15 (at 0.3 μM) changed the Hill coefficient ( n H) from 1 (control) to about 1.3 and 1.6, respectively. In (b), the inhibition by P 4 and P 15 decreased V and modified only slightly the K m values of the enzyme towards tRNA.