Chemical composition of O-(carboxymethyl)-chitins in relation to lysozyme degradation rates

O-Carboxymethyl chitin (CM-chitin) is a water-soluble derivative of chitin, be carboxymethylated in 3- and 6-positions to varying extents. CM-chitins with a total fraction of O-substitution from 0.65 to 1.5 were prepared, and characterised by high-field proton n.m.r. spectroscopy, allowing the determination of the fraction of O-substitution in positions 3 and 6, together with the fraction of N-acetylated units (F-A) The carboxymethylation in position 6 was found to be larger than in position 3 in all fractions, confirming that the reactivity at OH-6 is larger than at OH-3 in the carboxymethylation process. F-A of the CM-chitins varied from 0.85 to 0.95, showing no systematic variation with the total degree of carboxymethylation. These well-characterised CM-chitins were degraded with hen egg white lysozyme. Initial degradation rates, r: were determined from plots of the viscosity decrease (Delta 1/[eta]) against time of degradation at pH 5.3 and ionic strength 0.1 (M). It was found that the CM-chitin-lysozyme system obeyed a Michaelis-Menten type of kinetics. The time course of degradation of CM-chitin with lysozyme was non-linear, suggesting different degradation rates of different sequences in CM-chitin. All r-values of CM-chitins were higher than the highest rate determined for a partially N-acetylated chitosan with F-A Of 0.6. The r-values were found to increase with increasing F-A Of the CM-chitins, while r-values decreased with increasing fraction of carboxymethylation. Furthermore, the results suggest that carboxymethylation in position 3 has a larger effect on reducing the rate than carboxymethylation in position 6. (C) 1997 Published by Elsevier Science Ltd.