Identification of New Cystathionine Mono-Oxo Acids, S-(3-Oxo-3-carboxy-n-propyl) Cysteine and S-(2-Oxo-2-carboxyethyl) Homocysteine, in the Urine of a Patient with Cystathioninuria

Novel cystathionine mono-oxo acids, S-(3-oxo-3-carboxy-n-propyl) cysteine and S-(2-oxo-2-carboxyethyl) homocysteine, and cyclic amino acid, cystathionine ketimine, have been detected in the urine of a patient with cystathioninuria using liquid chromatography-mass spectrometry with an atmospheric pressure ionization interface system and an amino acid analyzer. To determine these cystathionine mono-oxo acids and cystathionine ketimine we took advantage of the selective absorbance at 380 nm of the phenylisothiocyanate-ketimine interaction product. The total concentrations of these compounds found in the urine samples of a cystathioninuric patient and six healthy subjects were respectively 3611.3 and 148.4 μg ± 35.9/g of creatinine. The cystathioninuric patient excreted 20 times more cystathionine mono-oxo acids in the urine than healthy subjects.