Thus, by measuring the diffusion properties of the conjugated protein, it is possible to distinguish between the two proposed models. NMR spectroscopy can be used to quantify the diffusion properties of conjugates by measuring the rotational correlation time (τc) of the conjugated protein. We determined τc values by measuring the N longitudinal (T1) and transverse (T2) relaxation times of the backbone. This approach has been used to quantitatively determine rotational correlation times for globular proteins up to ~25 kDa .