Cellulose pathways

The cellulose pathway branches at G6P where it is metabolized to UGP-glucose (UDPG), the direct precursor of cellulose. The biosynthesis of UDPG from glucose is a two-step enzymatic process involving phosphoglucomutase and UDPG-pyrophosphorylase. 

A comment on the properties of the base employed in reactions that involve the formation of the Vilsmeier-Haack adduct is in order, because several derivatives of cellulose are obtained by this route. Preparation of Cell-Tos has been attempted in LiCl/DMAc, by reacting the polymer with TosCl/base. Whereas the desired product was obtained by employing triethy-lamine, use of pyridine (Py) resulted in the formation of chlorodeoxycellu-lose. In order to explain these results, the following reaction pathways have been suggested [147] ... 

Fig. 11 Important synthetic pathways to regioselectivity in cellulose derivatives (R is H or sulfuric half ester), from [23]...

Sternberg, L.O., DeNiro, M.J. and Johnson, H.B. 1984 Isotope ratios of cellulose from plants having different photosynthetic pathways. Plant Physiology 74 557-561. 

Celluloses (native or microcrystalline) are organic sorbents. They have a low specific surface area and are applied mainly in partition chromatography, especially for the separation of relatively polar compounds. Works on the topic include those by Whitton and coworkers [8], who examined biosynthetic pathways for the formation of taurine in vertebrates. Taurine and its precursor amino acids were extracted from tissues, and the purified supernatant was spotted onto cellulose plates. The... 

Ghosh [548] used cellulose nitrate microporous filters (500 pm thick) as scaffold material to deposit octanol into the pores and then under controlled pressure conditions, displace some of the oil in the pores with water, creating a membrane with parallel oil and water pathways. This was thought to serve as a possible model for some of the properties of the outermost layer of skin, the stratum comeum. The relative proportions of the two types of channel could be controlled, and the properties of 5-10% water pore content were studied. Ibuprofen (lipophilic) and antipyr-ine (hydrophilic) were model drugs used. When the filter was filled entirely with water, the measured permeability of antipyrine was 69 (in 10 6 cm/s) when 90% of the pores were filled with octanol, the permeability decreased to 33 95% octanol content further decreased permeability to 23, and fully octanol-filled filters indicated 0.9 as the permeability. 

The series of degradation steps comprising mineralization is similar, whether the carbon source is a simple sugar (e.g., glucose), a plant polymer (e.g., cellulose), or a pollutant molecule [49,50,62 - 64,72,73]. Each degradation step in the pathway is facilitated by a specific catalyst (i. e., an enzyme) made by the degrading cell. Enzymes are found mostly within a cell (i. e., internal enzymes),... 

Figure 5.2 Probable thermal degradation pathways for cellulose, according to Fengel and Wegener...

Several products were also detected in base-degraded D-fructose solution acetoin (3-hydroxy-2-butanone 62), l-hydroxy-2-butanone, and 4-hydroxy-2-butanone. Three benzoquinones were found in the product mixture after sucrose had been heated at 110° in 5% NaOH these were 2-methylbenzoquinone, 2,3,5-trimethylbenzoquinone, and 2,5-dimethyl-benzoquinone (2,5-dimethyl-2,5-cyclohexadiene-l,4-dione 61). Compound 62 is of considerable interest, as 62 and butanedione (biacetyl 60) are involved in the formation of 61 and 2,5-dimethyl-l,4-benzenediol (63) by a reduction-oxidation pathway. This mechanism, shown in Scheme 10, will be discussed in a following section, as it has been proposed from results obtained from cellulose. 

Pyrolysis of biomass is defined as the chemical degradation of the biopolymers (cellulose, lignin and hemicellulose) constituting the wood fuel which initially requires heat. As can be seen in Figure 51, all reaction pathways making up the pyrolysis are not endothermic, which implies that some of the pyrolysis reactions generate heat. However, overall the pyrolysis process is endothermic. 

When ions permeate through cellulose acetate their transport pathways will tend to follow the regions where water is most concentrated. Thus they will meet and interact with the dissociated, fixed carboxylate ions. The concentrations of ions absorbed from salt solutions by swollen cellulose acetate are small for reasons connected with the low dielectric constant of the latter (2). The electro-chemical potentials of ions undergoing transport may therefore be influenced significantly by the presence of the fixed charges. Such influences are familiar with normal ion-exchange membranes. 

Some clues may be available from studies of the decomposition of lignin. Lignin constitutes the second most abundant carbon polymer on earth after cellulose (46). The understanding of biodegradative pathways of lignin and lignin-cellulosic polymers may elucidate the problems of reduced plant productivity associated with surface residues in conservation production systems. 

Succinic acid is commonly produced in microbes because it exists as a part of the TCA cycle, one of the ordinary metabolic pathways for production of energy. Several groups in the world are developing this production system to produce cheaper succinic acid from renewable resources like starch, glucose, cellulose and so on. If succinic acid could be produced from cheap carbon sources and the price were competitive with the petroleum-base product, many C4 chemicals could be expected as derivatives. 1,4-Butanediol is the typical one, which has a huge market. 

Plant cell walls are complex, heterogeneous structures composed mainly of polymers, such as cellulose, hemicelluloses, and lignins. In spite of several decades of research, cell wall assembly and the biosynthesis and ultimate biodegradative pathways of individual polymers are still far from being fully understood. One simple example will suffice Even today, no enzyme capable of catalyzing cellulose formation in vitro has been obtained. 

Cellulose, hemicelluloses, and lignin are the main components of cell walls in woody plants. For a long time, these plant polymers have stimulated the interest of many plant botanists and biochemists in terms of their biosynthetic pathways, functional interrelationships, and anatomical distribution. 

Though cellulose is one of the most important biopolymers, it has not yet been possible to completely elucidate its biosynthetic pathway, or establish exactly the cell organellae involved in its synthesis. However, during the last decade, the freeze fracture technique has been applied to investigate cell wall formation, and this has produced much information on the site where cellulose synthesis occurs. It is now generally accepted that both terminal and rosette complexes are responsible for cellulose synthesis (21). Our results (19,22) support that view. In a TEM-autoradiographic investiga-... 

Trichoderma species have a powerful set of well-characterized exoenzymes involved in the cellulolytic pathway exo-/ -l,4-glucanase which hydrolyzes amorphous and microcrystalline cellulose endo-/ -l,4-glucanase... 

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