The titration constants of some amides and dipeptides in relation to alcohol and formaldehyde titrations of amino-N.

MEASUREMENT of the titration constants of simple peptides is of biochemical interest for two reasons. Firstly, it provides information necessary for careful titrimetric estimation of amino-N in biological fluids or enzymic proteolysates [Richardson, 1934, 1, 2]. Secondly, it facilitates interpretation of protein titration curves by helping to define the change of titration constant which results from peptide formation [Cohn, 1931]. For gelatin hydrolysates and various synthetic dipeptides, suitable data are already available [Cannan and Muntwyler, 1930; Greenstein, 1933; and others]. There is therefore no difficulty in deducing the extent of error due to these substances in alkalimetric formaldehyde or alcohol titrations ofamino-N [Richardson, 1934, 2]. Yet there exists an important group of substances containing amino-N about which there has been insufficient information hitherto. These, the aminoacid amides, may be quite plentiful in certain plant extracts and probably of enzymic proteolysates [cf. Melville, 1935]. Titration constants for certain typical derivatives have therefore been examined, together with data for some peptides of possibly distinctive behaviour. In addition, the usefulness of isoglutamine as a readily synthesised buffer of value in peptidase experiments is described. EXPERIMENTAL.