Methylamine-induced conformational change of alpha 2-macroglobulin and its zinc (II) binding capacity. An X-ray scattering study.
Methylamine induces a conformational change of alpha 2-macroglobulin which is very similar to that obtained by proteinase reaction and binding. This was shown by small-angle X-ray scattering at 21 degrees C in 0.03 M Hepes buffer of pH 8.0 containing 0.15 M NaCl and 0.3 mM EDTA. When alpha 2-macroglobulin reacts with methylamine the side maximum virtually disappears from the X-ray scattering curve and the radius of gyration decreases from 7.8 nm to 7.2 nm. The X-ray data of alpha 2-macroglobulin are consistent with an open shape model similar to that deduced via electron micrographs [Schramm, H. J. and Schramm, W. (1982) Hoppe-Seyler's Z. Physiol. Chem. 363, 803-812]; one projection of the model resembles the letter H; the four subunits are mainly represented as elliptical cylinders which are connected via a central, quite flat cylinder. Zinc(II) ions cause aggregation of alpha 2-macroglobulin even at such a low total zinc concentration as 12.5 microM; for 25 microM zinc(II) concentration, the average molecular mass indicates that the aggregation goes beyond the dimeric stage. Monomeric species of alpha 2-macroglobulin appear to have the capacity specifically to bind 8.0 zinc(II) ions per molecule, which corresponds to two zinc(II) ions per subunit.
D055598:Chemical Phenomena; D002621:Chemistry; D006801:Humans; D008744:Methylamines / Q000494:pharmacology*; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D012542:Scattering, Radiation; D014965:X-Rays; D015032:Zinc / Q000378:metabolism*; D000511:alpha-Macroglobulins / Q000378:metabolism*
D008744:Methylamines; D000511:alpha-Macroglobulins; C027451:methylamine; D015032:Zinc