Quantification of D-aspartate in normal and Alzheimer brains

Using a new procedure to hydrolyze proteins without provoking racemization of the amino acids and using enzymatic methods to determine D- and L-aspartate (Asp), we have quantified the content of protein-bound D-aspartate (both D-aspartic acid and D-asparagine) of human brain white and gray matter proteins from normal and Alzheimer subjects. The D-enantiomer is present in brain proteins at mean concentrations between 0.48 and 0.90 mumol/g of wet tissue, corresponding to concentrations 34-82 times lower than that of L-aspartate. The highest levels of D-aspartate were found in Alzheimer gray matter (0.60-0.90, mean 0.69 mumol/g of wet tissue). When expressed as the percentage of total (i.e. D- plus L-) aspartate, %D = [D/(D + L)] x 100, the Alzheimer brains show a significantly higher content of D-aspartate in both gray matter (2.08%) and white matter (1.80%) than in the corresponding tissues of normal brains (1.65% in gray, 1.58% in white).