Characterization of a Blue Fluorophore Isolated from in Vitro Reaction of N-α-Acetyllysine and 3-Deoxyglucosone

Abstract

With the objective to investigate 3-deoxyglucosone (3-DG) mediated lysine crosslinks in vivo, we have isolated a lysine-3-DG-lysine crosslink from in vitro reaction of 3-DG and N-α-acetyllysine (NAL). This crosslink, named as furopyrrolopyridine crosslink (FPPC), has intense blue fluorescence with absorption maxima at 235, 270 and 370 nm and emission maximum at 470 nm. The absorption and fluorescence spectra of FPPC were not altered in pHs ranging from 2–12, but the characteristic spectrum of FPPC (at pH 7.0) disappeared when it was reduced with sodium borohydride. FAB-MS showed that FPPC has a molecular mass of 611, equivalent to the reaction of two molecules each of NAL and 3-DG with the concomitant loss of 5 molecules of water. NMR data showed that FPPC has a pyridinium ring and four free hydroxy groups. Since acid hydrolyzed FPPC can be detected by amino acid analysis, we have determined its levels in the acid hydrolyzates of proteins glycated by 3-DG or in the acid hydrolyzates of normal aged, cataractous, diabetic and brunescent human lens proteins as well as in the acid hydrolyzed glycated hemoglobin, A0.