A study by analytical ultracentrifugation on the interaction between lysozyme and extensively deacetylated chitin (chitosan)

Analytical ultracentrifugation (sedimentation velocity and sedimentation equilibrium) has been used for the first time to study the extent of complex formation between lysozyme and a chitosan extensively deacetylated to two levels (''C99'', 99% deacetylated and ''C99.9'', 99.9% deacetylated) at pH=4.5 and ionic strength, I=0.17 M. Sedimentation velocity experiments on mixtures of the two reactants (1 mg/ml chitosan and 0.1-0.6 mg/ml lysozyme) give clear evidence of an interaction between chitosan C99 and lysozyme and an indication of an interaction between lysozyme and chitosan C99.9. Sedimentation equilibrium molar mass analyses using the 'M* function' (Creeth & Harding, 1982) confirmed a clear interaction for C99:lysozyme and a weaker interaction between C99.9 and lysozyme. Further analyses by means of the 'omega function' (Nichol et al., 1976) to determine the fraction of free lysozyme in mixtures with defined total concentration indicated that essentially no free lysozyme(weight fraction <0.05) is present in the mixtures, irrespective of whether the concentration is monitored refractometrically or whether only the lysozyme constituent is monitored by means of the absorption optics. Copyright (C) 1996 Elsevier Science Ltd