FREE LYSINE, GLYCINE, ALANINE, GLUTAMIC-ACID AND ASPARTIC-ACID REDUCETHE GLYCATION OF HUMAN LENS PROTEINS BY GALACTOSE

The amino acids lysine, glycine, alanine, glutamate and aspartate form ed adducts with galactose at physiological pH and temperature as shown by incorporation of U[C-14] galactose, The percentage of galactose re acting with lysine, glycine, alanine, glutamate and aspartate was 4.5 to 7.8, 7.9 to 10.8, 3.2 to 4.6, 2.8 to 4.8 and. 3 to 5.2, respectivel y. Studies with lysine showed that the extent of glycation of the free amino acid increased with time, Incubation of lens homogenate with ga lactose, effected glycation of proteins. Addition of lysine in concent rations of 5 and 10 mM to equimolar concentrations of galactose decrea sed the glycation of lens proteins by 64% to 71%; glycine, alanine, gl utamate and aspartate decreased glycation by 23 to 68%, 32 to 61%, 35 to 56% and 26 to 61% respectively. Under similar conditions, glycine r eacts to a greater extent than lysine, alanine, glutamic and aspartic acids. However, lysine was more effective than glycine, alanine, aspar tic and glutamic acids in decreasing glycation of lens proteins by gal actose. The decrease of glycation with added lysine increased with tim e. In general increase of amino acid concentration rather than that of sugar augmented the decrease of glycation of lens proteins.