Ribonuclease A has been used as a model protein for studying the specificity of glycation of amino groups in protein under physiological conditions (phosphate buffer, pH 7.4, 37 “C). Incubation of RNase with glucose led to an enhanced rate of inactivation of the enzyme relative to the rate of modification of lysine residues, suggesting preferential modification of active site lysine residues. Sites of glycation of RNase were identified by amino acid analysis of tryptic peptides isolated by reverse-phase high pressure liquid chromatography and phenylboronate affinity chromatography. Schiff base adducts were trapped with Na- BH&N and the a-amino group of Lys-1 was identified as the primary site (80-90%) of initial Schiff base formation on RNase. In contrast, Lys-41 and Lys-7 in the active sitaec counted for about 38 and 29%, respectively, of ketoamine adducts formed via the Amadori rearrangement. Other sites reactive in ketoamine formation included Ne-Lys-1 (15%), N-Lys-1 (9%), and Lys-37 (9%w) hich are adjacent to acidic amino acids. The remaining six lysine residues in RNase, which are located on the surface of the protein, were relatively inactive in forming either the Schiff base or Amadori adduct. Both the equilibrium Schiff base concentration and the rate of the Amadori rearrangement at each site were found to be important in determining the specificity of glycation of RNase.
Published in Journal of Biological Chemistry, Volume 260, Issue 19, 1985, pages 10629-10636.
This research was originally published in the Journal of Biological Chemistry. Watkins NG, Thorpe SR, Baynes JW. Glycation of Amino Groups in Protein. Journal of Biological Chemistry. 1985; 260:10629-10636. © the American Society for Biochemistry and Molecular Biology.