Competitive binding of highly de-N-acetylated chitosans and N,N′-diacetylchitobiose to lysozyme from chicken egg white studied by 1H NMR spectroscopy
✍ Scribed by Are Kristiansen; Kjell M. Vårum; Hans Grasdalen
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 401 KB
- Volume
- 289
- Category
- Article
- ISSN
- 0008-6215
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✦ Synopsis
Chitosan is a linear polysaccharide which contains 2-acetamido-2-deoxy-/3-o-glucose (GlcNAc; A-unit) and 2-amino-2-deoxy-/3-D-glucose (GIcN; D-unit) residues linked through (1 ~ 4) glycosidic linkages. It has previously been shown that A-units and D-units are randomly distributed along the polymer chain in water-soluble, partially N-acetylated chitosans prepared by homogeneous or heterogeneous deacetylation of chitin [1,2]. Thus, the neighbourhood of units (e.g. the fractions of diads and triads) in the polymer is determined only by the fraction of acetylated units, F A (FAA = F~: FAD ~ FDA = FA * FD; FDD = FD 2; FAAA = ~2 etc.).
Lysozyme hydrolyses /3-(1 ~ 4) linkages in chitin. Berger and Weiser [3] showed that fully de-N-acetylated chitosan (F A = 0) is not degraded by lysozyme. Nordtveit et al. [4] reported that the initial degradation rate (by lysozyme from chicken egg white) of partially N-acetylated chitosans increases in proportion to F A to the power of 3.6, and that the degradation rate is negligible at low fractions of acetylated units (F A < 0.04). Lysozyme contains six binding subsites normally designated by the letters A-F, with cleavage occurring between sugar residues bound to subsites D and E. It has been suggested that subsites C, D, and E preferentially are occupied by A-units in productive enzyme-substrate complexes [5][6][7]. Accordingly, the chemical composition of the *