The ultraviolet spectrum of deoxyribonucleic acids and their constituents.

The spectra of deoxyadenylic, deoxyguanylic, deoxycytidylic and thymidylic acids are given at pH 1, 2, 3, 5 and 7, from 220 to 310 mμ. The spectrum of thymus DNA denatured in 0·l N-acetic acid at pH3, at low concentration, is almost identical to the calculated spectrum of its constituent nucleotides. The ratio of the absorbancies of DNA at 260 and 280 mμ reaches a constant value near pH 3, characteristic of the molar proportions of the bases. This appears to form the basis of a rapid method for estimating base composition.