The Composition of the Desoxypentose Nucleic Acids of Thymus and Spleen*

While the early workers in this field, such as Miescher and Hopne-Seyler, appear t,o have conjectured the macromolecular and complex chaaacter of the nucleic acids that they were the first to isolate, this view soon was abandoned in favor of the chemically more attractive tetranucleotide hypothesis, and those students of nucleic acid chemistry (e.g. (1, 2)) who still felt that much remained to be discovered worked against the current of their time. In the more recent past, the development of methods for the study and the characterization of high polymers has brought about a revival of interest in the chemistry of macro molecules occurring in nature. As regards the desoxyribonucleic acid of calf thymus, the high molecular character of this extremely asymmetric compoun’d has been demonstrated repeatedly (3-6). That this nucleic acid was considered as the prototype of all desoxypentose nucleic acids is understandable, since it is the only compound of its kind readily available for a detailed chemical investigation, but the implicit assumption on the part of many workers that desoxypentose nucleic acid is a single chemical individual, regardless of the source from which it is obtained, is incorrect. A comparison of the results contained in thk present communication with those submitted in an accompanying paper (7) will be of interest in this connection. A recent study from this laboratory (8), as well as a review article (9), has provided a fuller discussion of the pertinent literature. The problem of nucleic acid specificity also has been considered repeatedly (10, 11). The great part in the activities of the living cell, ascribed at present to the desoxypentose nucleic acids, makes it imperative to perfect a foundation that will make possible the direct consideration of problems of structure, composition, and specificity. Whatever chemical changes are produced in nucleic acids in the course of cellular development or by radiations or mutagens, such as the compounds of the mustard series, will hardly be of the kind that can be revealed by the mere inspection of optical or other physical characteristics.