216 HYDROGEN ION CONCENTRATION AND PEPSIN DIGESTION 



and also that the curves for the digestion and conductivity of the 

 hemoglobin fall further to the left {i.e. to the alkaline side) than do 

 the curves for the egg albumin. 



The experiments cannot be considered as showing quantitative agreement be- 

 tween the rate of digestion and the conductivity of the solution since the digestion 

 curve is given as the amount of protein decomposed in a certain time — a quantity 

 which is not connected in any simple way with the rate of digestion. They 

 are further complicated by the fact that the digestion in the region of the opti- 

 mum acidity represents approximately 50 per cent of the complete digestion of 

 the protein and therefore probably includes the secondary splitting of some of the 

 primary products of the hydrolysis, and not purely the action on the protein 

 itself. The conductivity on the other hand was measured on the protein solution 

 itself. It is not possible to carry the digestion curve much beyond pH 5.0 owing 

 to the rapid destruction of the enzyme. 



EXPERIMENTAL. 



Egg Albumin. — The egg albumin was crystallized three times as described by 

 Hopkins and Pinkus"^ and then dialyzed under pressure of about 150 cm. of 

 water at pH 4.8 until the specific conductivity of the solution was less than 

 1 X 10"'' reciprocal ohms. The solution was then diluted to 2 per cent with 

 water. Increasing amounts of HCl were added to a series of 50 cc. portions of 

 this solution and the total volume made up to 100 cc. 1 cc. of 2 per cent pepsin 

 was then added to 25 cc. of these solutions and placed at 25°C. 1 cc. of the solu- 

 tion was analyzed by the Van Slyke"^ method for amino nitrogen after 0, 8, 24, 

 and 36 hours. The curve given is the increase in cubic centimeters of amino nitro- 

 gen per cubic centimeter of solution after 24 hours. The 8 and 36 hour curves 

 were similar. 



Conductivity. — 1 cc. of inactivated pepsin was added to another 25 cc. portion 

 of the above solutions and the conductivity and pH of the solution were measured 

 at 25°C. The conductivity of the egg albumin salt was determined from the con- 

 ductivity of the solution by subtracting from the observed conductivity the 

 conductivity of HCI of the same pH (Northrop^^). 



Oxyhemoglobin. — Erythrocytes from fresh defibrinated ox blood were washed 

 with 7.8 per cent glucose solution until the conductivity of the suspension was 

 less than 1 X 10"'* reciprocal ohms. The cells were then laked with ether, sepa- 

 rated from the excess ether, and the ether in the solution removed in vacuo. The 

 solution was then diluted to contain about 1 cc. of amino nitrogen per cubic 

 centimeter as determined by the Van Slyke method. The conductivity of this 



21 Hopkins, F. G., and Pinkus, S. N., /. Physiol, 1898-99, xxiii, 130. 



22 Van Slyke, D. D., /. Biol. Chem., 1913-14, xvi, 121. 



