STUDIES ON THE SULPHUR METABOLISM OF TISSUES CULTIVATED IN VITRO: III. INTERRELATIONSHIPS BETWEEN CYSTEINE, METHIONINE, CYSTEAMINE, AND CYSTAMINE

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Abstract
Previous studies on the sulphur amino acid requirement of freshly-explanted chick embryonic heart tissues cultivated in vitro in completely synthetic media have been extended. The essential requirement for L-cystine has been found to be replaceable by L- but not by D-cysteine. In the presence of L-cysteine, the supplementary methionine requirement was found to be satisfied equally by the L- or D-isomer. Of eight derivatives and metabolites of cysteine studied only cysteamine showed any significant ability to replace cysteine or cystine. The activity of cysteamine was exhibited only in the presence of methionine. High levels of cysteamine were found to be strongly toxic and the toxicity could be reversed specifically bv L-cvsteine. Significantly less reversal of the cysteamine toxicity was effected by L-cystine, while other sulphydryl and disulphide compounds were ineffective. Cystamine was also found to be toxic to the tissue cultures and its toxicity could be reversed completely by L-cysteine and incompletely by L-cystine.