Conformational equilibrium of demetalized Concanavalin A: A reexamination of the kinetics of its interaction with Ca²⁺-ions and fluorescent saccharide

Two conformations of Concanavalin A have been reported by Brown et, al. [Biochemistry 16, 3883 (1977)]; one, named "locked," has a significantly greater affinity for both metal ions and certain saccharides than the other, the "unlocked" conformation. These authors recently reported a value of 0.14±0.01 for [PL] [P], the equilibrium ratio at 25°C, pH 6.4, of the concentrations of the locked to unlocked conformers of demetalized Concanavalin A [Brown et al., Biochemistry 21, 465 (1982)]. In a recent report, Strazza and Sherry [Biochem. Biophys. Res. Comm. 106, 1291 (1982)] concluded that "Concanavalin A will not assume the locked conformation in the complete absence of metals and that only trace amounts of Ca2+ can catalytically convert a significant amount of the protein into the locked conformation." These conclusions are incorrect, as shown here by a reexamination of their original kinetic data that underlie these published conclusions. The present analysis gives particular attention to the mathematical form that the data must satisfy throughout its range. The result is a value for [PL] [P] of 0.15 ± 0.02, in complete agreement with the earlier results of Brown et al. (1982). © 1982.