BIOLOGICAL INACTIVATION OF PROTEINS BY MAILLARD REACTION - EFFECT OF MILD HEAT ON TERTIARY STRUCTURE OF INSULIN

An average of 3.7 hexose residues bound the reaction amino groups of insulin [bovine pancreas] during 120 days of storage with D-[U-14C]glucose at 37.degree. C and 70% relative humidity. Dimethylaminonaphthalenesulfonylation of insulin reacted for 15 days corroborated the preferential binding at the N-terminal residues (A1-Gly and B1-Phe). While the acid solubility increased 10-fold at 15 days, suggesting dissociation of the hexamer into dimers, there was little or no change in its structural conformation as attested to by 2 biological functions. The 15-day Maillard insulin retained 78.2% of the ability to depress the level of blood glucose in rabbits, and 100% of its capacity to raise blood tryptophan in young rats. These results contrast with those for the reaction at 55.degree. C in which a larger number of sugar residues were demonstrated to bind the protein molecule during 1 mo. of storage. [Irreversible loss of nutritive value could occur in food proteins prior to the observation of extensive physicochemical changes.].