loop_
     _nef_covalent_links.chain_code_1
     _nef_covalent_links.sequence_code_1
     _nef_covalent_links.residue_name_1
     _nef_covalent_links.atom_name_1
     _nef_covalent_links.chain_code_2
     _nef_covalent_links.sequence_code_2
     _nef_covalent_links.residue_name_2
     _nef_covalent_links.atom_name_2
     B   3   CYS   SG   B   6   CYS   SG
     B   5   THR   OG1  B   9   GLN   C