Biological Inactivation of Proteins by the Maillard Reaction. Effect of Mild Heat on the Tertiary Structure of Insulin

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An average of 3.7 hexose residues bound the reactive amino groups of insulin during 120 days of storage with d-[U-14C]glucose at 37 °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 tenfold at 15 days, suggesting dissociation of the hexamer into dimers, there was little or no change in its structural conformation as attested to by two 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 °C in which a large number of sugar residues have been demonstrated to bind the protein molecule during 1 month of storage. © 1976, American Chemical Society. All rights reserved.

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Journal of Agricultural and Food Chemistry