CONFORMATIONAL CONTRACTION AND HYDROLYSIS OF HYALURONATE IN SODIUM-HYDROXIDE SOLUTIONS

The effects of NaOH on the conformations, interactions, diffusion, and hydrolysis rates of hyaluronate (HA) were characterized in detail using static light scattering (i) in the traditional ''batch'' mode (for conformations and interactions), (ii) in a time-dependent, simultaneous multiangle mode (for the hydrolysis rates), and (iii) coupled to HPLC for preliminary characterization of distributions of hydrolysis fragments. Strikingly, the conformations, interactions, and hydrolysis rates all seem to be controlled by the titration of the HA hydroxyl groups by NaOH to yield -O-, which (i) destroys single strand hydrogen bonds, leading to the very rapid destiffening and contraction of the HA coil and to a large decrease in intermolecular interactions, and (ii) leads to the slow intramolecular cleavage (hydrolysis) of glycosidic bonds. Remarkably, the root mean square radius of gyration R(g), the second virial coefficient A2, and hydrolysis rates all appear as mutually superposing titration curves which yield a pK of around 13. Interestingly, in contrast to classical ''non-draining'' coil molecules, the hydrodynamic radius of HA, as measured by dynamic light scattering, is independent of [NaOH] and the contraction of R(g).