JBC, Vol. 253, Issue 23, 8538-8544, Dec, 1978
Biphasic association of p-nitrophenyl 2-O-alpha-D-mannopyranosyl-alpha-D-mannopyranoside and concanavalin A as detected by stopped flow spectroscopy
T. J. Williams, J. A. Shafer, I. J. Goldstein and T. Adamson
Kinetics of binding of p-nitrophenyl
2-O-alpha-D-mannopyranosyl-alpha-D-mannopyranoside (M2) to concanaviln A
(con A) were examined. The time course of formation of a M2 . con A complex
is clearly biphasic, whereas the association with con A of p-nitrophenyl
2-O-methyl-alpha-D-mannopyranoside and other monosaccharides is a
monophasic process. The biphasic time course of the binding of M2 to conA
is most simply explained in terms of a model wherein the disaccharide can
bind to con A two different ways. In the initial rapid phase of the
biphasic reaction, both complexes form in amounts determined by the
relative values of the rate constants for association. In the subsequent
slow phase, the complexes equilibriate according to the relative values of
the initial constants for formation of each complex. The enthalpy of
activation for formation of the initial complexes with M2 is about 4
kcal/mol less favorable than for monosaccharides, whereas the entropy of
activations about 14 e.u. more favorable for binding of the disaccharide.
These differences in the activation parameters for binding M2 and
monosaccharides suggest that con A interacts simultaneously with groups on
both mannopyranosyl residues.
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