A STUDY BY ANALYTICAL ULTRACENTRIFUGATION ON THE INTERACTION BETWEEN LYSOZYME AND EXTENSIVELY DEACETYLATED CHITIN (CHITOSAN)

Analytical ultracentrifugation (sedimentation velocity and sedimentati on equilibrium) has been used for the first time to study the extent o f complex formation between lysozyme and a chitosan extensively deacet ylated to two levels (''C99'', 99% deacetylated and ''C99.9'', 99.9% d eacetylated) at pH=4.5 and ionic strength, I=0.17 M. Sedimentation vel ocity experiments on mixtures of the two reactants (1 mg/ml chitosan a nd 0.1-0.6 mg/ml lysozyme) give clear evidence of an interaction betwe en chitosan C99 and lysozyme and an indication of an interaction betwe en lysozyme and chitosan C99.9. Sedimentation equilibrium molar mass a nalyses using the 'M function' (Creeth & Harding, 1982) confirmed a c lear interaction for C99:lysozyme and a weaker interaction between C99 .9 and lysozyme. Further analyses by means of the 'omega function' (Ni chol et al., 1976) to determine the fraction of free lysozyme in mixtu res with defined total concentration indicated that essentially no fre e lysozyme(weight fraction <0.05) is present in the mixtures, irrespec tive of whether the concentration is monitored refractometrically or w hether only the lysozyme constituent is monitored by means of the abso rption optics. Copyright (C) 1996 Elsevier Science Ltd