Interactions of polynucleotides and their components. II. Interaction of uracil derivatives with alkali- and alkali earth chlorides.

During spectrophotometric titrations of uracil in different alkalior alkali earth chlorides, specific changes in the U.V. absorption of uracil at PH 12.0 have been observed. The spectra of 4-methyl and 5-methyl uracil change in the same way whereas 1-methyl and 3-methyl uracil are not influenced even by strong divalent cations. From spectrophotometric and Potentiometrie titrations I I it could be concluded that the changes are not due to the dissociation of the — HN(i) — C(6) = 0 groups. From the probable site of interaction it seems impossible that uridine or uridylic acid may be involved in such interactions. From optical density measurements the Ks value has been determined.