Conformational changes of bovine β-trypsin and trypsinogen induced by divalent ions: An energy-dispersive X-ray diffraction and functional study

The radius of gyration ( R g) of bovine trypsinogen and β-trypsin was measured by an energy-dispersive X-ray technique as a function of Ca 2+ or SO 4 2− concentration; these results have been supplemented with measurements of association equilibrium constants of Ca 2+ to its binding site(s) on both serine proteases and some of their adducts (with an effector and/or an inhibitor). As a whole, all information reported in the present work demonstrates that: (i) the strains exerted by different ions on these proteases produce diverse structural modifications; and (ii) at least in the case of Ca 2+, the changes in R g can be ascribed to the direct interaction of the binding site(s) on the protein matrix with the cation.