Spectral changes accompanying the interaction between metal ligands and concanavalin A

Interaction of calcium and manganese ions with apoconcanavalin A and sugar binding

“…The Mn2+ and Ca2+ concentrations in protein samples were occasionally determined by atomic absorption analysis and corresponded well to those expected, in contrast to the experience of others (Brown et al, 1977). It has been emphasized that care should be taken in checking the metal content of native Con A (Uchida & Matsumoto, 1972;Doyle et al, 1975). Apo-Con A was prepared by acid treatment of the protein (Kalb & Levitzki, 1968;Brewer et al, 1974).…”

“…Previous investigators have stressed the need to leave Mn2+ in contact with apo-Con A for considerable times before reproducible behavior is observed (Alter et al, 1977;Brown et al, 1977). The speeding up to the final MUM form when a Ca2+/Mn2+ mixture, rather than either ion alone, is added to apo is undoubtedly related to the observation that Ca2+ increases the binding of the manganese (Sherry & Cottam, 1973;Alter et al, 1977;Brown et al, 1977), alters the ESR of the manganese (Nicolau et al, 1969) and accentuates UV differences (Doyle et al, 1975). In addition there is an attendant overall change in protein conformation (Barber and Carver, 1975;Grimaldi and Sykes, 1975;Richardson and Behnke, 1976;Alter et al, 1977;Brown et al, 1977).…”

“…We were unable to determine directly the changes in situ of the concentration of free metal ion or protein-bound metal ion. Attempts using metal indicators (murexide and metalphthalein), calcium-ion selective electrodes, direct UV spectral changes (Doyle et al, 1975) and pH changes (Gachelin et al, 1972) were unsuccessful. The changes were either too small in magnitude or the response of the electrodes too sluggish to function effectively.…”

Phytohemagglutinins (Phytolectins)

“…Furthermore, occupation of the MnH-binding or transition metal-binding site (SI) is necessary before the second metal-binding site (S 2 ) can bind CaH, and the occupation of both sites is necessary before saccharide-binding can occur (1 17). More recent evidence, based on studies involving electron spin resonance (3 1, 279), circular dichroism (165), spin-lattice relaxation (13), and spectral changes (55), supports the view that the bonding of CaH to the S 2 site causes an alteration in the environment of the SI site, which, in tum, is important for the creation of the saccharide-binding site. Other studies (118,(244)(245)(246) have revealed that a variety of metals, including rare earth metals, may substitute for Mn 2 + on the S. transition site, including cadmium (Cd 2 +), cobalt (COH), nickel (NiH), zinc (Zn 2 +), lead (PbH), godalinium (Gd3+), terbium (Tb3+), and lanthanum (La3+).…”