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