An isolated RBP with at least one of the following characteristics: a) a
molecular weight of approximately 65-70 kDa and more preferably 66-69
kDa; b) a pI of greater than 10 or less than 3; c) a dissociation
constant of approximately 1.5.times.10.sup.-6 when bound to the rhamnose
moiety of solamargine; d) adapted to bind to a rhamnose affinity column
prepared according to example 1 and under the conditions set out therein;
e) adapted to be eluted from the column in example 1 with a 100 mM
rhamnose solution; f) insoluble in aqueous solution; and g) soluble in
highly denaturing buffers containing greater that approximately 2%
surfactant.