A procedure for the simultaneous preparation of S-sulfo-L-cysteine and L-alanine 3-sulfinic acid is described. The method is based on the quantitative reaction between sulfite and S-(2amino-2-carboxyethylsulfonyl~L-cysteine.
The yield was 95% for S-sulfo-Lcysteine and 9 1% for L-alanine 3-sullinic acid. The reaction was also applied to the quantitative determination of sulfite in biological materials. In this procedure, sulfite reacts with S-(2-amino-2-carboxyethylsulfonyl)-L-cysteine. Separation of the reaction product, S-sulfo-L-cysteine, is done by ionexchange fractionation, and it is determined with acid ninhydrin reagent 2 (M. K. Gaitonde, 1967, Biochem. J. 104, 627-663).
The recovery was 96.8 -+ 0.3%.
Sulfite is an intermediate formed in the oxidation of cysteine sulfur in mammals ( 1,2). In the course of our studies on urinary disulfides and metabolism of cysteine and cystine (3-lo), we found that S-(Zamino-2carboxyethylsulfonyl)+cysteine (ACESC)4 reacts quantitatively with sulfite to form Ssulfa-L-cysteine and L-alanine 3-sulfinic acid (11). The reaction scheme is shown in Fig. 1. S-Sulfo-L-cysteine is also formed from ACESC in the presence of aspartate aminotransferase and 2-oxoglutarate ( 12). The fact that Ssulfo-L-cysteine and L-alanine 3-sulfinic acid can be easily separated by cationexchange chromatography (11) prompted us to develop a method for the simultaneous preparation of S-sulfo+cysteine and L-alanine 3-sulfinic acid.
' Formerly the trivial name L-cystine disulfoxide was used. But its structure is not disulfoxide, but thiosulfonate (see Refs. (11,12)).
* 2-Amino-2-carboxyethyl sulfosulfane or L-alanine sulfosulfane.
3 L-Cysteine-sulfinic acid. 4 Abbreviation used ACESC, S-(2-amino-2-carboxyethylsulfonyl)-L-cysteine.