Loop F is covalently linked to Loop B of the same subunit, which in turn participates in the adjacent binding site acting as principal subunits and interacting with Loop E of the following complementary subunit. The movements of these structures are therefore linked and can be quantified by monitoring the distances involving representative residues. We are considering here three consecutive subunits: for clarity in the following the first is unlabelled, the second labelled with ′ and the third with ′′ . The selected residues (within the respective loops) include (+, Loop C)ASN219, (-, Loop F ′ )LYS189, (+, Loop B ′ )SER174 and (-, Loop E ′′ )SER145.