THE INTERACTION OF IONS AND DESOXYPENTOSE NUCLEIC ACID OF CALF THYMUS

Abstract

Analysis of the changes of optical density and of electrical conductivity that occur on addition of various salts to solns. of the nucleate were carried out. The salts used in the spectral studies included NaCl, KC1, Na2SO4, sodium citrate, MgCl2, BaCl2, CaCl2, SrCl2, MgSO4, and phosphate buffers. The addn. of any of the salts causes a max. lowering of about 15 to 18% in the value of the optical density at 260 m[mu]. The curves relating the extent of the lowering of absorption to the quantity of added salt are nearly the same for the salts of univalent cations, on the one hand, and those of bivalent cations, on the other. Far less of the salts of the bivalent cations is required, however, to produce the same degree of change. With bivalent cations the extent of lowering is detd. by the ratio of added cation to nucleate, and the lowering is essentially complete when approx. 0.8 equivalent of cation per atom of DNA P has been added. These results were interpreted to indicate a tight binding of bivalent cations by the nucleate. A comparison was made of the increases of conductivity that occur when successive increments of various salts are added to water or to solns. of the nucleate. Such studies were carried out with NaCl, Na2SO4, MgCl2, MgSO4, CaCl2, and BaCl2. The results were interpreted to indicate a tight binding of approx. 0.82 equivalent of bivalent cation per atom of DNA phosphorus. Similar expts. with alkali-treated nucleate are also presented.