Several types of measurements have been used to investigate cooperativity in homodimeric enzymes: (i) detection of occupancy status of ligands in the active sites: the presence of both subunits in apo or holo form hints to PC, while presence of a ligand (substrate or inhibitor) only in one binding site suggests NC; (ii) the ligand input-output response measure: if a low ligand concentration leads to basically no output whilst a larger ligand content leads to almost maximal output, PC may be operative. However, if ligand depletion is considered, such response can also be characteristic of NC (especially when the ligand is appreciably depleted due to very high binding affinity) . The situation is further complicated by the fact that NC cannot be distinguished from independent binding at multiple sites by equilibrium measurements . These two situations are not identical over the complete time courses of the binding reaction; but so far, the proposed approaches in pre-equilibrium conditions to distinguish between a NC model and a model where independent binding to multiple binding sites occurs, can only evaluate how well the models fit the data, but not infer on the model itself . (iii) The value of the Hill Coefficient (HC), detected by input/output curves' slopes: HC greater than 1 suggests PC, whereas lower than 1 hints to NC . However, this criterion has been criticized because (1) it assumes that ligands bind to enzyme simultaneously , although ligand binding can alter the subunit-dimer equilibrium becoming not simultaneous; (2) it does not consider the possibility that HC can be greater than 1 for covalent ligands, irrespectively of the nature of cooperativity . (iv) The symmetric nature of the homodimer structure: fully symmetric subunits may be characteristic of PC while asymmetric ones (both in the apo form and in the doubly occupied form) may be specific for NC .