Brett C T
Plant Molecular Science Group, Institute of Biomedical and Life Sciences, University of Glasgow, United Kingdom.
Int Rev Cytol. 2000;199:161-99. doi: 10.1016/s0074-7696(00)99004-1.
Cellulose occurs in all higher plants and some algae, fungi, bacteria, and animals. It forms microfibrils containing the crystalline allomorphs, cellulose I alpha and I beta. Cellulose molecules are 500-15,000 glucose units long. What controls molecular size is unknown. Microfibrils are elongated by particle rosettes in the plasma membrane (cellulose synthase complexes). The precursor, UDP-glucose, may be generated from sucrose at the site of synthesis. The biosynthetic mechanism may involve lipid-linked intermediates. Cellulose synthase has been purified from bacteria, but not from plants. In plants, disrupted cellulose synthase may form callose. Cellulose synthase genes have been isolated from bacteria and plants. Cellulose-deficient mutants have been characterised. The deduced amino acid sequence suggests possible catalytic mechanisms. It is not known whether synthesis occurs at the reducing or nonreducing end. Endoglucanase may play a role in synthesis. Nascent cellulose molecules associate by Van der Waals and hydrogen bonds to form microfibrils. Cortical microtubules control microfibril orientation, thus determining the direction of cell growth. Self-assembly mechanisms may operate. Microfibril integration into the wall occurs by interactions with matrix polymers during microfibril formation.
纤维素存在于所有高等植物以及一些藻类、真菌、细菌和动物中。它形成含有结晶变体纤维素Iα和Iβ的微纤丝。纤维素分子长度为500 - 15,000个葡萄糖单位。控制分子大小的因素尚不清楚。微纤丝由质膜中的颗粒状玫瑰花结（纤维素合酶复合体）拉长。前体尿苷二磷酸葡萄糖可能在合成位点由蔗糖生成。生物合成机制可能涉及脂质连接的中间体。纤维素合酶已从细菌中纯化出来，但尚未从植物中纯化出来。在植物中，被破坏的纤维素合酶可能形成胼胝质。纤维素合酶基因已从细菌和植物中分离出来。纤维素缺陷型突变体已得到表征。推导的氨基酸序列提示了可能的催化机制。尚不清楚合成是在还原端还是非还原端发生。内切葡聚糖酶可能在合成中起作用。新生的纤维素分子通过范德华力和氢键结合形成微纤丝。皮层微管控制微纤丝的取向，从而决定细胞生长的方向。可能存在自组装机制。微纤丝在形成过程中通过与基质聚合物相互作用整合到细胞壁中。
