Concanavalin a will not assume the sugar binding conformation in the complete absence of metal ions

Concanavalin A (Con A) is known to exist in two conformations that differ in their capacity to bind metals and sugars. The conformation that binds metals tightly and has a high affinity for sugars is termed the "locked" form and the conformation with low affinity for sugars and binds metals weakly is termed the "unlocked" form. It has recently been reported [Brown, et al. Biochemistry 21, 465(1982)] that apo-Con A will form the locked conformation in the absence of metals to the extent of 12.5% when equilibrated at 25°C for one week. In this report we show that Con 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.