(sis'tēn, sis'tin),
An isomer of cystine in which the configuration about one of the α-carbons is d, about the other, l, so that the molecule as a whole possesses a plane of symmetry and is optically inactive. Note that meso-cystine is not dl-cystine. dl-cystine is a racemic mixture of dd-cystine and ll-cystine.
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