Electron staining of reducing ends evidences a parallel-chain structure in Valonia cellulose
✍ Scribed by Kaoru Hieta; Shigenori Kuga; Makoto Usuda
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1984
- Tongue
- English
- Weight
- 1012 KB
- Volume
- 23
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
A major unsolved problem in cellulose structure is the polarity of adjacent chains of cellulose in the microfibrils, namely, the "parallel or antiparallel" problem. This issue is closely related to the possibility of a folded-chain structure and to the mechanism of cellulose biosynthesis. The prevailing view, based on x-ray (and electron) diffraction,I4 is that native celluloses (Cellulose I) are arranged in parallel and that regenerated celluloses (Cellulose 11) are antiparallel. However, the limited size of single cellulose crystals hinders obtaining convincing results, and conflicting views are not yet ruled out? In this study, we attempted to obtain direct evidence of the molecular arrangement of cellulose in microfibrils, using a novel method with electron microscopy. When properly prepared fragments of microfibrils are selectively stained with a heavy metal at the reducing end groups, either of the two modes of staining could be observed, according to the molecular arrangement, as in Figure 1.
The cell wall of Vulonia (a kind of green algae) is a convenient material for structural studies of cellulose because of its high crystallinity and exceptional microfibril width. However, it is not degraded to microcrystallites merely by heating with acids, because of its defect-free structure, so the microcrystallites were prepared as follows. Vesicles of Vulonia macrophysa purified by successive alkali and acid treatments2 were disintegrated to microfibrils by a laboratory homogenizer; at the same time the microfibrils were damaged, showing