The change of ultraviolet absorption of thymo-nucleoprotein and thymo-nucleic acid with pH

Thymo-nucleoprotein prepared according to Mirsky and Pollister and nucleic acid prepared therefrom, following the method of Gulland et al., show a sharp increase in ultraviolet absorption at pH 11.0–11.3 by a factor of 1.32–1.33 times their absorption in neutral solution. The change in the wavelength of the maxima is very small. The absorption at pH values lower than 11 can be calculated by simple addition of the absorption of the four purines and pyrimidines in the nucleic acid. At a pH higher than 11 the special characteristics of the purines and pyrimidines in situ are supposed to give the increase in maxima absorption.