The isolation and identification of 2-methyl-2,4-thiazolidine dicarboxylate as a by-product in the conversion of cysteine to glucose in the perfused rat liver.

Cysteine is one of the more toxic amino acids, however the toxic agent associated with cysteine toxicity has not been identified. Recently it was shown that 2-methyl-2,4-thiazolidine dicarboxylate (MTD) was formed fromcy steine by rat liver and would be toxic to the rat. This suggested that MTD formed by the rat liver can be produced both enzymatically and by chemical interaction between cysteine and another compound, possibly pyruvate. When MTD (1 mmol/rat) was injected into 6 rats, two of them died. Only 70-80% of the MTD was excreted within 24 h, suggesting an accumulation of MTD. It is possible the MTD could accumulate in the tissues until it reached a toxic concentration. Whether this could account for the death associated with cysteine toxicity is unknown.