The Chemistry of the Nucleic Acids and Nucleoproteins

Isolation of nucleoproteins.-Many methods for isolating nucleoproteins involve a stage, either during the extraction or more generally in the precipitation process, which is relatively drastic and may produce an alteration in the chemical and physical properties of the nucleoprotein ; thus the majority of preparations involve precipitation of the extracted material with hydrochloric or acetic acids. The extraction processes vary considerably and employ water (1 to 13), dilute alkaline solution (14 to 17), sodium chloride solution (18, 19, ZO), or buffer solutions of pH values ranging from 4 to 11 (21 to 26), followed in each case by precipitation with acid. It has been suggested (27) that nucleoproteins prepared thus are of variable composition, the precipitated nucleic acid carrying with it varying quantities of loosely bound protein, and these methods are now considered unsatisfactory (28) in view of the possible rupture of the nucleic acid-protein bond during the acid precipitation. A more controlled extraction of liver nucleoprotein is that in which the tissue was treated with a solution containing 0.03M sodium bicarbonate and 0.5M potassium chloride (29, 30) and the nucleoprotein precipitated by adjusting the solution to pH 4.2. Even these conditions may, however, be too drastic, and more recently attention has been concentrated on modifications of the original mild methods (1 to 11, 15), coupled with precipitation of the nucleoprotein with saturated ammonium sulphate (12, 31) or calcium chloride (6, 7, 32) solutions. Thus an early method (32) has been modified (33) whereby fresh pulped calf thymus is extracted with water at 5” C. for twenty-four to thirty-six hours, and after clarification of the extract the nucleoprotein is pre-