Studies on nucleoproteins. III. Deoxyribonucleic acid complexes with basic polyelectrolytes and their fractional extraction.

The fractionation of deoxypentose nucleic acids, recently reported from this laboratory (1, 2), is essentially based on the fractional extraction of nucleohistone or artificial histone nucleates with salt solutions of increasing concentration in the presence of a chloroform phase. In this manner, a series of fractions of regularly graded composition (falling proportions of guanine and cytosine, rising proportions of adenine and thymine) is obtained. The fact that fractionation can be effected has been confirmed by others, eit,her through the use of gradient elution from a histone-kieselguhr column (3) or in an arrangement in which the time of contact with the salt solution was varied rather than the concentration of the latter (4). The unity relationships ‘previously stressed (5) and recently reviewed (6) were preserved in all fractions isolated in this laboratory. In regard to its electrostatic properties, a deoxyribonucleic acid may be viewed, around pH 7, as a negatively charged polyelectrolyte, similar to a polyphosphoric acid, and histone as a basic polyelectrolyte not unlike a polyamine. In the instances cited above the fractionation of the nucleic acid was achieved by means of its reversible interaction with histone or globin. It appeared of interest to determine whether the electrostatic properties of the reacting compounds were the principal bases of the fractionation process or whether some structural peculiarities of the protein were also responsible. For this reason, the reaction of sodium deoxyribonucleate preparations from calf thymus with strongly electropositive synthetic polyelectrolytes was studied. One of the compounds, polylysine, is a macromolecular basic polypeptide and, on this account, not dissimilar to a basic protein, such as histone. Polyvinylamine, on the other hand, differs greatly from a protein, as it consists of a hydrocarbon chain to which amino groups are attached directly.