Small‐Angle X‐Ray Scattering Study of the Interaction between Human α2‐Macroglobulin and Trypsin

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Abstract
The interaction between human .alpha.2-macroglobulin and [bovine pancreas] trypsin yields a complex of 2-trypsin molecules and one .alpha.2-macroglobulin molecule as the main product. This is indicated from small-angle X-ray titration measurements in 0.02 M Tris/HCl buffer of pH 7.40 containing 0.2 M NaCl and 5 mM EDTA. The radius of gyration for the complex was determined to be 7.1 nm. The complex formation coincides with a decrease in the 1st side maximum of the scattering curve for .alpha.2-macroglobulin. A comparison of the experimental data with those calculated from various models indicates that the data are consistent with the scattering from a hollow cylinder containing 2 sites, each of which is partly filled with 1 trypsin molecule.