fumarate + L-cysteine => S-[(2R)-succino]-L-cysteine
fumarate + l-cysteine => s-[(2r)-succino]-l-cysteine
fumarate + L-cysteine => S-[(2R)-succino]-L-cysteine
fumarate + l-cysteine => s-[(2r)-succino]-l-cysteine