Productive and unproductive lysozyme-chitosaccharide complexes. Equilibrium measurements.

A method to determine both productive and unproductive lysozyme-chitosaccharide complexes has previously not been available. The method described in this paper uses a dye, Biebrich Scarlet, which forms a 1:1 complex with only part of the substrate binding site. Complex formation perturbs the spectrum of the compound and thus its dissociation constant can be determined (K-D equals 0.13 mM). The dissociation constants for three major enzyme-chitooligosaccharide complexes have also been determined: (1) chitooligosaccharides that bind only to sites A-C of lysozyme perturb the spectrum of the Biebrich Scarlet-lysozyme complex, without affecting the dissociation constant of the dye (K-u equals 0.01 mM); (2) chitooligosaccharides that interact with sites D-F displace the dye (K-S' equals 5-15 mM); (3) chitohexose forms a complex which involves the whole binding site and, therefore, also displaces Biebrich Scarlet. This complex, with a dissociation constant K-S equals 0.03 mM, is considered to be the productive one. The binding mechanism proposed on the basis of the results in this paper differs significantly from those considered previously.