Protein-Carbohydrate interaction

Abstract

Concanavalin A yielded a monodiperse pattern in the analytical ultracentrifuge in the pH range 2-5. The sedimentation coefficient, sOZ~,~ in pH 5 acetate buffer containing 0.1 M NaCl (total I'/2 = 0.20) was 4s. At pH 7 and above, a two-peak schlieren pattern was observed, the faster component (about 7s) probably representing a dimer. On the basis of an s~o.~ of 3.9s; a D 20.~ of 5.43 X 10-T cm2/second, and a P of 0.73 ml/gm, a molecular weight of 68,000 was calculated (0.10 M acetate, NaCl, I?/2 = 0.45) for the homogeneous component at pH 5. From free-boundary electrophoresis data the isoelectric point of concanavalin A was determined to be 7.1 f 0.1. Starch gel electrophoresis patterns of concanavalin A in borate buffer (pH 8.6) were characterized by an anodically migrating streak. Incorporation of n-glucose into the gel gave a single sharp band which migrated slowly toward the cathode, the glucose probably inhibiting protein-starch interaction. Gel filtration experiments with Biogel P-100 suggested that at pH 5 the molecular weight of concanavalin A is in the vicinity of 50,000; at pH 7.5 concanavalin A is completely excluded, an indication that a high molecular weight species probably is formed by the association of subunits. Concanavalin A has an extinction coefficient, E&, of 11.4 f 0.1, the molar ratio Mtyrasine/

Unusual Fragments in the Subunit Structure of Concanavalin A

“…We have isolated from this mixture a polypeptide chain that has a molecular weight of 27,000 by equilibrium sedimentation in guanidine HCl. Previous data on the molecular weight of Con A in nondissociating solvents gave values of about 55,000 at pH 5.0 (25,26) and of about 100,000 at higher pH (25,27 In addition, recent crystallographic evidence has shown that the molecule exists as a dimer located on a two-fold axis (30). The pairing of two subunits, each of molecular weight 27,000, on a two-fold axis in our model is consistent with this data, although the possibility of higher molecular symmetry cannot be excluded.…”

Spectral changes accompanying the interaction between metal ligands and concanavalin A

“…Metal-free con A contained 0.012 moles Mn2+ and 0.16 moles Ca2+, respectively, per mole con A subunit. Con A concentrations were determined spectrophotometrically, assuming that 1 .O mg/ml gives an absorbance of 1.14 at 280 nm with a 1 cm pathlength [8].…”

The Biochemistry of Plant Lectins (Phytohemagglutinins)

“…First, lectins may appear in multiple forms that possess similar biological activities and that differ only slightly in their chemical properties (19,20,22,(36)(37)(38)(39)(40). Second, many lectins are comprised of subunits and undergo complex association-dissociation reactions, giving rise to multiple forms of the same lectin that differ in molecular size (41,42).…”