Detection of aspartic acid enantiomers by chiral capillary gas chromatography. Determination of in vivo racemization and reduction of metal-induced background.

Racemization of aspartyl residues in proteins is a post-translational process, related to ageing. A method is presented for the detection of aspartic acid enantiomers in protein hydrolysates, based on chiral capillary gas chromatography. It is fast, easy and preferable to the usual diastereomeric dipeptide technique. We present evidence that traces of metals that are extracted from the glassware during acidic hydrolysis are the main cause for high background racemization, which often troubles accurate measurements. Effective ways to reduce this background and its standard deviation to acceptable levels are discussed, and a mathematical approach to correct for background racemization is given. Hydrolysates of aged human eye lens proteins were used to demonstrate the enantiomeric separation.