Conformational changes of bovine beta-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 beta-trypsin was measured by an energy-dispersive X-ray technique as a function of Ca2+ or SO42- concentration; these results have been supplemented with measurements of association equilibrium constants of Ca2+ 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 Ca2+, the changes in R-g can be ascribed to the direct interaction of the binding site(s) on the protein matrix with the cation. (c) 2006 Elsevier Inc. All rights reserved.