Cellulose from the cell wall of the green alga Microdictyon tenuius was studied by electron diffraction. The diffractograms disclose two distinct crystalline phases. The major phase has a one-chain, triclinic (PI) structure with unit cell parameters of a = 0.674 nm, b = 0.593 nm, c (chain axis) = 1.036 nm, a = 117°, 0 = 113°, and y = 81°. The crystal unit cell of the minor component has two chains and is monoclinic (P2i), with a -0.801 nm, b = 0.817 nm, c (chain axis) = 1.036 nm, and y the monoclinic angle = 97.3°. The triclinic phase is metastable, and annealing it in dilute alkali at 260 °C converts it into the monoclinic form. The presence of two phases in Microdictyon can be extended to other algal celluloses and is consistent with the biphasic character deduced from 13C CP/MAS NMR spectroscopy. The triclinic and the monoclinic structures correspond to the la and Id spectra, respectively.
A microfocus synchrotron wide-angle diffraction mapping experiment was used to analyze
the crystalline microstructure and the polymorphism of a series of C-starch granules from smooth pea.
In these specimens that globally contained 60% of A-phase and 40% of the B-allomorph, it was found
that the two phases were present in each granule. The A-allomorph was located essentially in the outer
part of the granules whereas the B-phase was found mostly at their center. In the A-component, the
diffraction diagrams were always poorly oriented fiber patterns with the fiber axis systematically oriented
toward the center of the granule. On the other hand, in the B-center, only powder diagrams could be
observed whereas in middle zones of the granules, the B-component was much better oriented than the
A-component.
The 1,4-@D-glucan cellobiohydrolase I (CBHI) from Trichoderma reesei was labelled with 4-6 nm gold particles. This CBHI-gold complex still retains 60% of the original CBHI activity and allows good visualization of the enzyme adsorbed at the surface of cellulose mirofibrils or microcrystals. The main features of the adsorption are: rapid and irreversible binding; preference of the crystal edges instead of the crystal surface for the binding; the absence of specificity for the crystal tips where the cellulose chain ends are supposedly located.
Colloidal gold Enzyme labelling Adsorption
1,4-P-D-Glucan cellobiohydrolase CelluloseElectron microscopy (Trichoderma reesei)
Mannan-rich plant cell walls were mechanically disintegrated and chemically extracted in order to ascertain their morphology and structure by electron microscopy and electron diffraction. For Acetabularia crenulata and Codium fragile, the cell-wall fragments were found to consist of alkali-resistant fibrillar mannan II encrusted with alkali-soluble granular mannan I. In the case of ivory nuts (Phytelephas macrocarpa) there is, in addition, a microfibrillar cellulose component which was also identified. The mannan I-mannan II polymorphism was also obtained when various mannan fractions were recrystallized from solution. In these recrystallizations, the occurrence of one or the other polymorph was found to depend on several parameters: the molecular weight of the mannan, the temperature of crystallization and the polarity of the crystallization medium.
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