PYRRALINE ETHER CROSS-LINKS AS A BASIS FOR PROTEIN CROSS-LINKING BY THE ADVANCED MAILLARD REACTION IN AGING AND DIABETES

Pyrraline (formyl-5-hydroxymethyl-pyrrol-1-yl)-L-norleucine) is an adv anced Maillard reaction product derived from the reaction of glucose w ith lysine amino group on proteins, Its presence in plasma and tissue proteins has been established by immunological and chromatographic met hods, The purified preparation of pyrraline obtained from the reaction of glucose with lysine when stored at room temperature or at refriger ation turned pink in color, suggesting spontaneous formation of degrad ation products, These products were analyzed by high-performance liqui d chromatography and one of the products was isolated to purity, The s tructure of the compound was established to be a dipyrraline formed by an ether bond between two pyrraline molecules, This finding led us to investigate the reactivity of pyrraline with thiol and hydroxy amino acids, The hydroxy amino acids were in general nonreactive, except hyd roxy lysine and hydroxy proline which formed minor condensation produc ts. While the reaction of cysteine resulted in the formation of two di stinct thioethers, the reaction of glutathione resulted in the formati on of two major unidentified compounds which gradually degraded upon i ncubation, These data suggest that pyrraline formed in vivo can furthe r react with other amino acids on proteins to form crosslinks, which m ay explain in part increased protein crosslinking associated with agin g and diabetes. (C) 1996 Academic Press, Inc.