Purification of Pepsin

Since 1836, when Theodor Schwann signalized the presence in gastric juice of the proteolytic ferment which he was the first to designate as pepsin, a large number of attempts have been made to isolate it in a pure form to determine its chemical nature and its ultimate physiological properties. In a large majority of these, and, especially, all those made before 1895, except that of Brticke (I), who was the first to use adsorption, the methods used would not now be regarded as adequate for the purpose, and the results they gave are, accordingly, now only of historic interest in relation to the subject. In consequence a detailed reference to them will be omitted here and only such citations of the later publications to which we owe what at present we know about pepsin will be made in this contribution on the subject.* Pekelharing (2), by dialyzing, at low temperature, against distilled water, gastric juice from a dog with a Pavlov fistula, till the concentration of hydrochloric acid in the juice was decreased to about 0.02 per cent, precipitated the pepsin therein as a finely divided suspension. This suspension he separated by centrifuging and, after washing the sediment with distilled water, dried it in a desiccator. From the clear fluid left after centrifuging he precipitated, by half saturation with ammonium sulfate, more pepsin which was then freed from this salt by dialysis and, after the addition of hydrochloric acid to the extent of 0.2 per cent, was subjected to dialysis against distilled water, thus furnishing an additional quantity of pure pepsin. The average composition of the pepsin so prepared was C 51.99, H 7.07, N 14.44, S 1.63, Cl 0.49, P 0.01 per cent. The phosphorus found in pepsin Pekelharing regarded as due to traces of an impurity resulting from the digestion of a phosphorus-containing protein. The chlorine, on the other hand, he found to be constant, even in preparations obtained by dialysis with oxalic acid. He obtained a coagulated product of an acid character on heating either gastric juice or purified pepsin in acid solution, to which he gave the name