On the mode of union of certain proteins with acids and bases.

Abstract

Considerable experimental evidence has in recent years been brought forth which indicates that the union of proteins with acids and bases takes place by chemical combination.¹ It has been suggested by Robertson² that the −COHNgroups in the protein molecule are responsible for the acid and base-combining capacity but this hypothesis has been recently questioned by ourselves.³ Kossel and Cameron⁴ pointed out many years ago that the acid-combining capacity of salmin is equal to the combining capacity of the guanidine groups in the arginine, and Bracewell⁵ has carried this idea further by showing in a number of proteins a close agreement between the acid-combining capacity and the sum of the free amino nitrogen and the amino group of arginine which does not react with HNO₂. The recent work of Hitchcock⁶ in which he determined the acid-combining capacity of gelatin and of deaminized gelatin affords an opportunity for checking this hypothesis and our calculations which are given in Table I show an excellent agreement between the calculated and the experimental results.