N~(alpha)-(1-Deoxy-D-fructos-1-yl)-L-histidine ('D-Fructose-L-histidine'):a Potent Copper Chelator from Tomato Powder

摘要

Dried fruits and vegetables are known for their high content of D-fructose-amino acids,or Amadori compounds,which appear at the initial step of the Maillard reaction and may participate in redox reactions mediated by trace metals.In this study,we investigated complexation between Cu(II)and N~(alpha)-(1-deoxy-D-fructos-1-yl)-L-histidine(D-fructose-L-histidine,FruHis).The content of FruHis in two types of commercial tomato powders was estimated by GLC-MS,using single ion monitoring of trimethylsilylated FruHis hydroxyoximate,as 40 mg/100 g,whereas the concentration of free histidine in the powder samples was about 53 mg/100 g.The Cu(II)-binding ability of FruHis was studied along with structurally related molecules L-histidine,dipeptide L-camosine,and N~(alpha)-O-deoxy-D-fructos-1-yl)-L-arginine(FruArg)at 25 °C using pH-potentiometric titrations.Analysis of the titration curves showed that formation of Cu(II)-FruHis complex species occurs at pH values as low as 2 and that the complexes were redox stable in the pH range 2-10.5,at least for the time of the experiment.At physiological pH,Cu(II)and FruHis form a dominant coordination species of composition MLH_(-1)(log beta = 5.67),with a presumably deprotonated anomeric hydroxyl group of the fructose portion.The apparent stability constant of 1:1 complexes formed by FruHis and Cu(II)in neutral aqueous solutions is about 10~4 times higher than similar values calculated for L-histidine,L-carnosine,and FruArg.FruHis nearly completely protected hydroxyl radical-mediated fragmentation of polymeric DNA in the presence of the Cu/H2O2/ascorbate system,whereas neither of the reference compounds could inhibit the DNA fragmentation as efficiently in similar conditions.These results warrant further investigation of FruHis as a potential food-related antioxidant.