A Method for the Fractional Analysis of Incomplete Protein Hydrolysates

The constituents of an enzymatic hydrolysate of protein can be divided according to their complexit,y into six fractions; protein, metaprotein, proteose, peptone, subpeptones, and amino acids. A method for the quantitative estimation of these fractions was devised in order to secure more definite information regarding the changes occurring during hydrolysis than is obtained by the usual free amino nitrogen determinations. The method has stood the test of continued use by different workers for over a year, and has given consistently accurate results. Briefly, the method involves the precipitation of the protein by trichloroacetic acid, of the metaprotein by careful adjustment of the reaction, of the proteoses by NazSOl a6 33”C., of the peptones by tannic acid under definitely fixed conditions; and the determination of the residual amino acids and simple peptides by a slight modification of the alcohol precipitation methods of Folin and Denis (1) and Van Slyke and Meyer (2). No new principle is introduced, but quantitative results with these reagents were found to be obtainable only under rigidly fixed conditions. The metaprotein fraction is determined on a separate aliquot of the original solution. For the assay of the other five fractions 100 cc. are required, containing not less than 200 mg. of nitrogen. The amount of each fraction is estimated by the nitrogen content, obtained by difference before and after filtration.