Article,
Sequence specificities for lysozyme depolymerization of partially N-acetylated chitosans
Canadian Journal of Chemistry-Revue Canadienne de Chimie, 73 (11): 1972 -- 1981 (November 1995)
Abstract
The influence of sugar residue sequence in partially N-acetylated
chitosans on relative hydrolysis rate catalyzed by lysozyme was studied.
The relative rates were modelled assuming an Arrhenius-type relation
for the relative rate constants. The apparent activation energy was
assumed to consist of additive contributions from GlcN or GlcNAc
residues within the polymer chain interacting with sites A-F of the
active cleft of lysozyme. This model accounted well for the relative
hydrolysis rates reported for well-defined oligomers. Calculated
and experimental data for the dependence of the initial relative
hydrolysis rates on fraction of acetylated units, F-A, showed an
F-A(3,6) dependence. A fully water-soluble highly N-acetylated chitosan
with F-A = 0.68 was depolymerized using lysozyme for further testing
of the model. Analyses of the C-13 nuclear magnetic resonance spectra
of the diad sequences at the new reducing and nonreducing ends formed
by lysozyme showed that this enzymatic depolymerization was dominated
by chitosan sequences presenting GlcNAc residues to sites C, D, and
E of the active cleft. In contrast, there was no selectivity between
GlcNAc and GlcN residues interacting with site E These selectivities
were confirmed by the calculated contributions to the apparent activation
energy of these sites. The experimentally determined depletion in
the diad and triad frequencies of GlcNAc during the course of lysozyme
hydrolysis was in good agreement with the model calculations.
Tags
- ;
- ;;
- c-13-nmr
- chitin;
- chitins
- chitosan;
- chitosans;
- deacetylated
- degradation;
- field
- h-1-nmr;
- lysozyme;
- model
- nmr-spectroscopy;
- sequence
- specificity;
- subsite
- [isi:]
