Studies on the determination of total nucleic acids by ultraviolet absorption methods.

Ultraviolet absorption methods for the study of nucleic acids have become increasingly useful since the quantitative relationships between nucleic acids and their absorption of ultraviolet light have been shown by Caspersson (1). For example, ultraviolet measurements provide a rapid and simple means of determining the total nucleic acid (TNA) value which may be used to verify the TNA value arrived at by summing the results of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) analyses found by calorimetric methods. Acid hydrolysis depolymerizes nucleic acids extensively and results in an increased ultraviolet absorption, the value for which is quite reproducible for the same material. The acid hydrolysis also releases purine-bound sugars for their reaction with various chromogenic reagents. Hence the calorimetric assays and determination of TNA by ultraviolet absorption may be performed on the same acid hydrolysate. Trichloroacetic acid (TCA) is commonly employed as the hydrolytic agent because it is also an excellent protein precipitant. Recent investigations of the application of ultraviolet absorption methods to measurement of TNA in TCA hydrolysates of mammalian tissues have been reported by Tsuboi (2) and Logan et al. (3). As shown by Logan et I& TCA absorbs strongly in the region of nucleic acid absorption (255 to 265 mp) and in a range whereby its absorbancy is changing rapidly with wave length over a small wave length interval. Moreover, during the heating to accomplish the hydrolysis, TCA is partially lost, probably through decomposition. The studies to be reported here are concerned with further investigations of ultraviolet absorption methods as applied to TCA hydrolysates of biological materials.