43Ca and 67Zn NMR spectra of Ca2+, Zn2+-concanavalin A solutions

The half-band width of 43Ca NMR of free aqueous Ca2+ was scarcely increased by adding more than equal molar apo-concanavalin A(apo-Con A), suggesting that slow chemical exchange, koff less than 10 s-1, occurs for the Ca2+ ion from Con A. In contrast with the 43Ca NMR findings, the half-band width of 67Zn NMR of free aqueous Zn2+ was markedly increased by adding apo-Con A. The 67Zn NMR half-band width of Zn2+ in the presence of apo-Con A was decreased by adding excess Ca2+, but was increased by adding excess D-mannose. These changes of the half-band width were influenced mutually by D-mannose or Ca2+, respectively. The broadened half-band widths of Zn2+ in the presence of Con A were decreased by adding Mn2+, suggesting that Mn2+ was substituted for Zn2+ at a metal binding site of Con A.