Sunlight induces N-epsilon(carboxymethyl) lysine formation from glycated polylysine-iron(III) complex

Sunlight was found to strongly induce the formation of N-epsilon-(carboxyme thyl)lysine (CML) from glycated polylysine in the presence of Fe(III) ion. The initial step of this Fe(Ill)-catalyzed CML formation was noted to be si milar to that of blueprint photography as was confirmed by the production o f Turnbull's blue in sunlight-exposed glycated human serum albumin ferricya nide solution in the presence of Fe(III). Based on this, photoinduced oxida tive C-C bond cleavage of the Amadori compound was assumed to be initiated by photochemical single electron transfer from ligand to Fe(III) in the Fe( III)-Amadori compound complex affording the Fe(II)-Amadori compound radical intermediate, which eventually yields either CML or active oxygen species. CML is thus a useful oxidative stress marker. The mechanism proposed here would explain the high accumulation of CML in lens protein and skin actinic elastosis.