PREPARATION PRESERVATION AND PROPERTIES OF HIGH MOLECULAR WEIGHT POLYADENYLIC ACID

Polyadenylic acid of a high degree of polymerization (S20,w = 20 S) was synthesized by use of polynucleotide phosphorylase from Micrococcus lysodeikticus. A simple “falling-object” viscometer was developed for assaying the polymerization reaction at low shear stress with adequate accuracy. During purification of the polymer it was noticed that extensive dialysis against glass-distilled water caused degradation of the polymer. We demonstrated that the polymer is not degraded if dialysis is carried out against a neutral electrolyte solution or against a 0.1 m buffer solution of pH 4.0, approximately the pH established inside the membrane when the polymer is dialyzed against water. In agreement with the sedimentation data of Fresco and Doty (Fresco, J. R., and Doty, P. (1957), J. Am. Chem. Soc. 79, 3928), spectral measurements indicate that polyadenylic acid is in the protonated helical form following water dialysis. We tentatively conclude that the electrostatic interactions are sufficiently large in the absence of salt to promote dramatically the chemical hydrolysis of the backbone chain. Melting curves were measured for the helix-coil transition of the protonated double-helical form present at acid pH. It was found that the transition curve for the high molecular weight sample (S20,w = 20 S) is considerably sharper than that for a commercial sample with S20,w = 8.2 S. This latter sample is therefore of a size range where equilibrium melting properties are not yet independent of molecular length. © 1969, American Chemical Society. All rights reserved.