title: Manganese, calcium, and saccharide binding to concanavalin A, as studied by ultrafiltration.
abstract: The binding of the ligands Mn2+, Ca2+, and methyl alpha-D-glucopyranoside to concanavalin A, purified as described (A.J. Sophianopoulos and J.A. Sophianopoulos (1981) Prep. Biochem. 11, 413-435), was studied by ultrafiltration in 0.2 M NaCl, pH 5.2 and pH 6.5 to 7, and at 23 to 25 degrees C. The association constant (Ka) of methyl alpha-D-glucopyranoside to concanavalin A was (2 +/- 0.2) X 10(3) M-1, both at pH 5.2 and 7. At pH 5.2 and in the absence of Ca2+, the Ka of Mn2+ to concanavalin A was (5 +/- 1) X 10(3) M-1, and in the presence of 1 mM Ca2+, the Ka was (9.1 +/- 2.1) X 10(5) M-1. At pH 6.5 Mn2+ bound to concanavalin A with a Ka of (7.3 +/- 1.8) X 10(5) M-1, and the binding affinity was virtually independent of the presence of Ca2+. Experiments of binding of 4-methylumbelliferyl alpha-D-mannopyranoside to concanavalin A indicated that at pH 5.2, binding of a single Mn2+ per concanavalin A monomer was sufficient to induce a fully active saccharide binding site. Ca2+ is not necessary for such activation, but rather it increases the affinity of concanavalin A for binding Mn2+.
mesh_terms: D002118:Calcium / Q000378:metabolism*; D003208:Concanavalin A / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006923:Hymecromone / Q000031:analogs & derivatives / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D014462:Ultrafiltration; D014468:Umbelliferones / Q000378:metabolism*
chemical_list: D014468:Umbelliferones; D003208:Concanavalin A; C008512:methylumbelliferyl-alpha-D-mannopyranoside; D006923:Hymecromone; D008345:Manganese; D002118:Calcium