The isolation of some hitherto undescribed products of hydrolysis of proteins. — Part IV

In the course of certain researches on the chemistry of gelatin carried out in this laboratory, it was found that the Hausmann numbers obtained for a given sample of gelatin showed considerable variations, depending upon the preliminary treatment of the sample. In particular, the diamino-nitrogen (i. e ., the nitrogen precipitated by phosphotungstic acid) was found to vary from about 20 per cent, to as much as 30 per cent, of the total nitrogen. It was found that if the gelatin were hydrolysed directly with boiling acid, a constant value for the diamino-nitrogen, of the order of approximately 20 per cent, of the total nitrogen, was obtained ; if, however, the gelatin were allowed to stand with acid in the cold, prior to hydrolysis, the value for the diamino-nitrogen rose considerably, in some cases by as much as 9 per cent. It has therefore been the practice in this laboratory, in hydrolysing a protein, to add the protein to the boiling acid, thus minimising any effect produced by standing with acid prior to hydrolysis ; by this method, consistent results are obtained. Further, it was suggested by Knaggs (loc. cit .) that the increased nitrogen found in the diamino-fraction was due to the formation of peptides, which were resistant to hydrolysis, and were precipitated by phosphotungstic acid. The present research had for its object the investigation, qualitatively and quantitatively, of the substances (peptides or other) causing this increase in diamino-nitrogen. In the course of the work, no peptides were isolated, and no indication of their presence was discovered; the whole of the increased diamino-nitrogen could be accounted for by (a ), increases in two of the bases (lysine and arginine) known to be present, and (b ) the presence of a base (dl -lysine) which has not previously been recognised as a normal hydrolysis product of the proteins, but which has been prepared by other means. The properties of this base are therefore well known. It does not apparently arise by mere racemisation of the lysine already known to be present in the protein, as ordinary active lysine was also obtained, in quantity rather more than normal. The origin of this base is still unknown. It is probably derived from some other unknown constituent of the protein, from which it is set free by the action of acids acting only in the cold.