INTERACTION OF AMINO-ACIDS AND GELATIN WITH UREA

The pH titration of nine amino acids (glycine, proline, valine, serine , glutamine, tryptophan, arginine, histidine and aspartic acid) in pre sence of urea in the concentration range 1-8 mole dm-3 has been perfor med. The results support suppression of the first dissociation constan t (K1) of the amino acids and acceptance of H+ ions by the amide formi ng uronium ion (UH+). The second dissociation constant (K2) of the ami no acids is affected relatively weakly by urea. Quantitative evaluatio n of different species existing in solution and the degree of dissocia tion of the acids as well as the degree of binding of H+ ion to the am ide have been made. It has been found that the polarity of the aqueous -urea medium does not straight forwardly correlate with the altered pK 1 of the amino acids. Urea can also affect the pH-titration behaviour of gelatin with an increase of the intrinsic pK of the acidic groups o f the protein by 0.45 unit.