Tiie Joijrnal of Bioloqical Ciiem~~ry

The observation of Boman and Kaletta (I, 2) that venom phosphodiesterase is capable of hydrolyzing the so called native thymus deoxyribonucleic acid has been confirmed in several laboratories (3-5). Boman (6) noticed that under appropriate conditions the reaction may be carried almost to completion. All these experiments were performed with comparatively crude preparations of phosphodiesterase. In the present paper the progress of degradation of deoxyribonucleic acid by highly purified phosphodiesterase has been followed by three independent methods: pH-stat titration, viscosimetry, and spectrophotometry. Similar measurements were made with pancreatic deoxyribonuclease I (a typical endonuclease) and with micrococcal deoxyribonuclease. The results were compared, and they led to the conclusion that phosphodiesterase degrades deoxyribonucleic acid to completion, essentially by exonucleolytic action (7).