The Conditions for Complete Hydrolysis of Proteins

Henriques and Gjaldbaek,l in an article devoted chiefly to a study of the above subject with the form01 titration, find that, when proteins are hydrolyzed with acid, both amino nitrogen and ammonia increase up to a certain point, at which the amino nitrogen attains its maximum. When hydrolysis is continued beyond this point, a transformation of amino nitrogen into ammonia follows, indicating a deaminization of some amino-acid or acids. The point at, which the amino nitrogen reaches a maximum, with the least possible formation of ammonia, they define as the end point of the hydrolysis. From the results of acid hydrolyses performed under various conditions Henriques and Gjaldbaek conclude that the most certain method for obtaining the above end point is treatment with 3~ hydrochloric acid in an autoclave at 150” for one and one-half hours. With casein, Witte peptone and calves’ flesh, complete hydrolysis could also be obtained by boiling with 20 per cent hydrochloric acid for twelve hours. With egg albumin, however, the results were different. The amount of amino nitrogen present after six hours’ boiling with 20 per cent acid was only 89 per cent of that obtained by autoclave hydrolysis, and continuation of the boiling for six hours more resulted in no increase. From this it appeared that, in egg albumin at least, some peptid linkings exist in such an unusually stable condition that they can be split only by the autoclave hydrolysis. Both Osborne and Guest2 and the writer3 have based protein analyses on the assumption that hydrolysis is complete when the