MORPHOLOGY OF NATIVE CELLULOSE RELATED TO THE BIOLOGICAL SYNTHESIS

In the 1930's, the chemical structure of cellulose chains was resolved and models of the crystal lattice of native (Cellulose I) and merceri zed cellulose (Cellulose II) were presented. Optical microscopy in the 1800's had shown a fibrillar morphology of mu m dimension for native cellulose. Electron microscopy with metal shadow casting, applied abou t 1950, revealed a microfibrillar morphology of 5 to 10 mn dimension f or native cellulose of plant, bacterial and animal origin. In the auth ors' work (1952), the microfibrills with Cellulose I lattice were cons idered to be formed by a biological (enzymatic) process. Based on enth alpy data for the mercerization of native cellulose, the Cellulose I l attice was found to be in a thermodynamically metastable state in rela tion to Cellulose II. The cell walls of the primitive marine algae Hal icystis were an exception. They showed an irregular membrane morpholog y, containing Cellulose II, as expected for the crystallization of the free chains. Later work by the author in the 1960's, using deuterium and tritium exchange of never-dried native bacterial and wood cellulos e, revealed that cellulose is formed and directly deposited as crystal line microfibrils with the Cellulose I lattice. Recent work on the bio genesis of cellulose microfibrils by R. M. Brown ef nl. in Austin, Tex as supports these concepts. Elementary fibrils of about 3 nm width and Cellulose I Lattice are shown to be extruded through the bacterial ce ll wall of Acetobacter, as a product of a series of active enzymes, cl oned to identified genes. Certain strains of Acetobacter and Halicysti s algae form Cellulose II with folded chains, because they do not have the complete enzyme system for elementary fibril formation. Kobayashi et nl. in Sendai Japan, cooperating with Brown's group, have synthesi zed cellulose chains in vitro using purified cellulose enzymes and flu orinated cellobiose as monomer. Even elementary cellulose microfibrils with Cellulose I lattice are formed in this in vitro system. The rese arch work by Brown and Kobayashi on cellulose biogenesis has given a d eep insight into the life process in an important area.