MEASUREMENT OF EXCITATORY SULFUR AMINO-ACIDS, CYSTEINE SULFINIC ACID,CYSTEIC ACID, HOMOCYSTEINE SULFINIC ACID, AND HOMOCYSTEIC ACID IN SERUM BY STABLE-ISOTOPE DILUTION GAS-CHROMATOGRAPHY MASS-SPECTROMETRY ANDSELECTED-ION MONITORING

Oxidized sulfur-containing amino acids are recognized as agonists of e xcitatory amino acid receptors in the mammalian nervous system. Homolo gues of glutamic acid (homocysteine sulfinic acid and homocysteic acid ) and aspartic acid (cysteine sulfinic acid and cysteic acid) have bee n shown to be agonistic to N-methyl-D-aspartate receptors in animal br ain and have been demonstrated in brain tissue. Considerable evidence exists for the role of homocysteic acid and cysteine sulfinic acid as endogenous ligands for excitatory amino acid receptors. We report, for the first time, the quantitation of these compounds in normal human s erum, by a newly developed gas chromatography-mass spectrometry method that employs stable isotope-dilution selected ion monitoring using in ternal standards prepared in our laboratory. We also report new method s of synthesis of stable isotope-labeled internal standards used in me asuring cysteine sulfinic acid, cysteic acid, homocysteine sulfinic ac id, and homocysteic acid. (C) 1994 Academic Press, Inc.