Degradation to sulphate of S-methyl-L-cysteine sulphoxide and S-carboxymethyl-L-cysteine sulphoxide in man

A nearly complete recovery of radioactivity was achieved over 14 days following the oral administration of [³⁵S]-S-methyl-L-cysteine sulphoxide and [³⁵S]-S-carboxymethyl-L-cysteine sulphoxide to four healthy male volunteers. The urine was the major pathway of excretion of radioactivity (c. 96% in 0-14 days; c. 59% in 0-24 hours), with the faecal route being relatively unimportant (c. 1.7% in 0-3 days). Inorganic sulphate was an important degradation product, incorporating a substantial proportion of radioactive sulphur derived from these molecules (c. 40% in 0-14 days; c. 20% in 0-24 hours). Subtle differences were noted in the pattern of radioactive sulphate excretion following administration of the two cysteine-sulphoxide compounds, suggesting that their sulphur-containing moieties may enter different catabolic routes.