A fluorimetric study of the lanthanides binding to Concanavalin A

Abstract

1. 1. The bincling of Tb 3+ and other lanthanides to Con A has been studied by sensitized Tb 3+ luminescence, by quenching of intrinsic fluorescence and by activity measurements. 2. 2. In all the experimental conditions tested, it was found that holo and apo Con A bind lanthanide ions at a site different from the bincling sites of the constitutive metals, Mn 2+ and Ca 2+. 3. 3. The bound lanthanide did not affect the saccharide bincling ability and the hemoagglutinating ability of Con A. 4. 4. The intrinsic fluorescence of Con A is quenched by the bincling of Tb 3+ and Gd 3+. The same quenching is obtained by shifting the pH of Con A from pH 6.5 to 4.5. 5. 5.It is proposed that H + and Ln 3+ completely quench a tryptophan, perhaps the residue 88 or 182.