preferred_name: an L-alpha-amino acid + L-proline => Xaa-L-Pro dipeptide + H2O
preferred_name_lc: an l-alpha-amino acid + l-proline => xaa-l-pro dipeptide + h2o
label: an L-alpha-amino acid + L-proline => Xaa-L-Pro dipeptide + H2O
label_lc: an l-alpha-amino acid + l-proline => xaa-l-pro dipeptide + h2o