POLYNUCLEOTIDE PHOSPHORYLASE - ANOMALOUS VISCOSITY CHANGES OBSERVED DURING POLYMERIZATION OF NUCLEOSIDE DIPHOSPHATES

Reaction mixtures containing buffer, nucleoside diphosphate, magnesium ion and polynucleotide phosphorylase of Escherichia coli exhibit a high, transient viscosity during polymer synthesis. The magnitude of this viscosity depends on the reaction conditions, particularly on the concentration of enzyme, the level of Mg++, and the presence or absence of oligonucleotides with free 3′‐hydroxyl groups. The viscosity observed during polymer formation is markedly dependent on concentration, a property not shared by solutions of isolated poly U. The number average molecular weight of poly U synthesized by polynucleotide phosphorylase changes only from approximately 58,000 to 70,000 during a time interval where there is a ten‐fold change in reduced viscosity. Binding studies using Millipore filters suggest the formation of an enzyme‐polynucleotide complex. The observed transient viscosity is considered to result from either (a) the enzymic redistribution of nucleotides from extremely long polymer chains formed initially in the reaction medium, or (b) from the formation of a slowly dissociating enzyme‐multiple polynucleotide complex. Copyright © 1969, Wiley Blackwell. All rights reserved