The Spreading of Pepsin and of Trypsin

The pepsin was obtained in the form of a 5 per cent solution in glycerol (1 cc. containing 50 rag. of pepsin). I t was diluted tenfold before use with 0.01 s hydrochloric acid (pH 2). 5 ram. 8 were blown out of a calibrated micropipette on the surface of the water in a Langmuir tray according to the method which we have used for several years. Effect of pH.--The effect of pH on the amount of the spreading has been studied. For this purpose dilute hydrochloric acid solutions between pH 1 and 3, a 1/300 molar sodium acetate-acetic acid solution between pH 3.6 and 5.6 (or 1/350 molar veronal acetate buffer solutions according to Michaelis), and mixtures of HCI 1/300 s and Na~CO8 1/300 N were used. I t was possible to show that, as a rule, the influence of pH is the same as that observed with other proteins. The maximum was again a