A reaction of glucose with peptides.

Valylhistidine (Val-His) reacts with glucose (Glc) in a mixture of pyridine and acetic acid to form glucosylvalylhistidine (Glc-Val-His). The pK of the alpha-amino group is thereby lowered to about 5.6 as judged by electrophoretic mobility. The reaction: [Formula: see text] also occurs in an aqueous solution of pyridine and acetic acid of pH6.2 at 50 degrees C, in which it exhibits a half-time of about 30h and a dissociation constant of about 0.3m. Isoleucyltyrosine and glucose react similarly in aqueous solution. The Glc-Val-His has the chromatographic, electrophoretic and chemical properties reported by Holmquist & Schroeder (1966a) for the substance released by proteolysis from the N-terminus of the beta-chains of haemoglobin A(Ic); the value of the dissociation constant means that the concentration of haemoglobin A(Ic) found naturally could be explained by reaction of haemoglobin A with the blood glucose.