FREE ALANINE, ASPARTIC-ACID, OR GLUTAMIC-ACID REDUCE THE GLYCATION OFHUMAN LENS PROTEINS

The amino acids lysine and glycine are reported to react with glucose at physiological pH and temperature and undergo non-enzymic glycation. Three other amino acids present in relatively larger amounts in the l ens i.e. alanine, aspartic acid and glutamic acid were also found to u ndergo non-enzymic glycation as found by incorporation of uniformly la belled (U-[C-14]) glucose into the amino acids. The glucose incorporat ion was 1.6 to 2.5% for alanine, 35 to 50% for aspartic acid and 2.3 t o 3.3% for glutamic acid. Each amino acid of varying concentrations lo wered the extent of in vitro glycation of lens proteins significantly in glucose-treated homogenates of normal lens from humans. The decreas e in glycation for alanine was between 32 and 69%, that for aspartate was between 18 and 74%, and for glutamate was between 52 to 74%. Decre ased glycation was greater for higher concentrations of glucose. Scave nging of intracellular glucose and decreasing the extent of glycation of lens proteins could be the mechanism of action by which the amino a cids alanine, aspartic acid and glutamic acid could exercise a benefic ial effect on cataract and diabetic retinopathy.