pH effects on the hyaluronan hydrolysis catalysed by hyaluronidase in the presence of proteins: Part II. The electrostatic hyaluronan – Protein complexes

Hyaluronan (HA) hydrolysis catalysed by hyaluronidase (HAase) is enhanced when bovine serum albumin (BSA) is present and competes with HAase to form electrostatic complexes with HA. At 1 g L−1 HA and BSA concentrations, BSA is able to form three types of complexes with HA depending on pH ranging from 2.5 to 6: insoluble neutral complexes at low pH values, sedimentable slightly charged complexes at pH near 4 and soluble highly charged complexes at pH near 5. The BSA content, charge and solubility of the HA–BSA complexes increase when pH is increased up to the pI of BSA. The normalised charge excess does not exceed 20% for the sedimentable complexes and 40% for the soluble complexes. It has been shown that the sedimentable slightly charged HA–BSA complexes are the most efficient to compete with HAase and release it. All the HA–BSA complexes are hydrolysable by HAase. The HA–BSA binding site shows that one BSA molecule is associated with 85–170 HA carboxyl groups, depending on pH. Similar results have been obtained for lysozyme over an extended pH domain, including the neutrality.