Complex formation between protein and poly vinyl sulfonate as a strategy of proteins isolation

The complex formation between the basic protein trypsin and the strong anionic polyelectrolyte poly vinyl sulfonic acid was studied by using turbidimetric and isothermal calorimetric titrations. The trypsin–polymer complex was insoluble at pH lower than 5, with a stoichiometric ratio polymer mol per protein mol of 1:136. NaCl, 0.5 M inhibited the complex precipitation in agreement with the proposed coulombic mechanism of complex formation. The protein structure and its thermodynamic stability were not significantly affected by the presence of the polyelectrolyte. The enzymatic activity of trypsin increases throughout time, even in the presence of the polymer.