Dynamics of Lysozyme-Saccharide Interactions

The interaction of lysozyme with di- and with tri-N-acetylglucosamine has been studied by the temperature jump relaxation method at pH 6.0, approximately 28.7°, ionic strength = 0.1 m. A single relaxation process is observed in the time range of 10 µsec to 100 msec, in both di- and trisaccharide-lysozyme solutions. No relaxation process is observed in the same time range in lysozyme solutions not containing saccharides. The bimolecular rate constants (k1) and dissociation rate constants (k-1) have been obtained for the lysozyme-saccharide interactions from the concentration dependence of the relaxation times. The rate constants (k1) are virtually identical (4.5 x 106 m-1 sec-1) for both the di- and the trisaccharide-lysozyme interaction, but the dissociation rate constant (k-1) for the disaccharide is over 30 times larger than that for the trisaccharide. The ratio of rate constants k1/k-1 is in good agreement with apparent binding constants obtained independently by other methods. A molecular explanation of these results is given in terms of the recent crystallographic data on lysozyme-saccharide complexes.