Tre Dissociation Constants of Certain Amino Acids.*

Various attempts (14) have been made to correlate the acidand base-combining capacity of proteins with the content of certain of the amino acids. As better analytical data have become available, this correlation has become closer, but it is made somewhat uncertain by lack of accurate knowledge of the ability of certain amino acids to combine with acid and with base. Ultimately, this correlation must also take into consideration the stereochemical structure of the protein molecule. It has been previously pointed out (5) that values for the dissociation constants of oxyproline, &hydroxyglutamic acid, and serine are still lacking. To this list we can add isoleucine and norleucine. To make the list complete there should also be added several other recently discovered amino acids. Our knowledge of these is, at the present time, too fragmentary to warrant attempting work of the nature herein described. Moreover, the dissociation constants for glutamic acid were determined by somewhat inadequate methods (6). Harris (7) has published the dissociation constants for valine, but without titration curves, and with an omission in the tables, making it desirable to repeat the determination of the constants for this amino acid.’