Bacteria monomeric mechanism

Electron-microscope investigation of cultures of bacteria has shown that the cellulose elements are not a physical appendage of the cell, but occur free and are scattered within the medium.This discovery has raised questions as to the processes or steps involved in the formation of the microfibrils and the extent to which they are influenced by cell organelles or carried out by exogenous chemical interactions and mechanical forces. Ohad and coworkers considered that the steps involved may be resolved into (a) polymerization of the activated, monomeric precursor to form cellulose molecules of high molecular weight, (b) transport of the molecule from the site of synthesis to that of crystallization, (c) crystallization or fibril formation, and (d) orientation of fibrils during deposition. 

A central role in the biosynthesis of isoprenoids is filled by the isopentenyl diphosphate-dimethylallyl diphosphate isomerase (IDl) that catalyzes the interconversion of IPP and DMAPP. The necessity for such an enzyme was suggested in the 1950s when only IPP was known as a monomeric isoprenoid precursor, but an allylic diphosphate such as DMAPP was assumed to have the higher intrinsic reactivity for polyisoprenoid synthesis [22, 88, 89]. The first enzymatic isomerization of IPP to DMAPP was observed in 1959 from a cell-free extract of baker s yeast [90, 91]. Two types of IDI with essentially no amino acid sequence or structural similarities are able to catalyze this interconversion by completely different enzyme mechanisms. The well-known IDI-I have been identified in animals, plants, fungi, and bacteria, whereas the IDI-II can be found mainly in archaea but also in some bacteria [92, 93]. 

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