Biosynthesis of Ethanol

Fig. 8.4 The glycolysis pathway in Saccharo-myces and the biosynthesis of ethanol and glycerol. Compounds DHAP, dihydroxyl-acetone monophosphate Fru6P, D-fructose-6-phosphate Frul,6P2, D-fructose-1,6-bisphosphate GA3P, D-glyceraldehyde-3-phosphate GL3P, sn-glycerol-3-phosphate GLAP2, phosphoglycerate-3-phosphate ...

Biosynthesis of ethanol renewable feedstock and enzyme catalysis (p. 11)... 

Enzymes are remarkably efficient catalysts, but they are also labile (sensitive) to such factors as heat and cold, changes in pH, and various specific inhibitors. In the first experiment of this chapter you will have an opportunity to observe the biosynthesis of ethanol and to test the effects of various agents on the enzyme system. 

Phosphatidylethanolamine synthesis begins with phosphorylation of ethanol-amine to form phosphoethanolamine (Figure 25.19). The next reaction involves transfer of a cytidylyl group from CTP to form CDP-ethanolamine and pyrophosphate. As always, PP, hydrolysis drives this reaction forward. A specific phosphoethanolamine transferase then links phosphoethanolamine to the diacylglycerol backbone. Biosynthesis of phosphatidylcholine is entirely analogous because animals synthesize it directly. All of the choline utilized in this pathway must be acquired from the diet. Yeast, certain bacteria, and animal livers, however, can convert phosphatidylethanolamine to phosphatidylcholine by methylation reactions involving S-adenosylmethionine (see Chapter 26). 

Many drugs interact with folate to affect its absorption, antagonize its biochemical activity, or increase its loss from the body. These drugs include ethanol, phenytoin, and oral contraceptives. Salicylates can compete with foUc acid for plasma protein binding. Methotrexate, a cytotoxic agent, is a folate antagonist that inhibits the biosynthesis of this coenzyme. 

Nonphysiological compounds have also been described as influencing the overall metabolism of sialic acid. Administration of ethanol (2 g/kg) to rats significantly decreases the sialic acid content of brain tissue.246 Convulsions induced by pentylenetetrazole (6,7,8,9-tetrahy-dro-5/f-tetrazoloazepine) are accompanied by a diminution in the rate of biosynthesis of polysialogangliosicles GT, and GQn, in rat brain.227 Such ManNAc analogs as 2-acetamido-l,3,4,6-tetra-0-acetyl-2-deoxy-D-mannopyranose or the 2-(trifluoroacetamido) derivative lead to a marked lowering of the incorporation of radioactivity from labelled ManNAc into glycoconjugate sialic acids of murine, erythroleukemia (Friend) cells.247... 

The biosynthesis of fatty acids occurs extramitochondrially and by a set of enzymes that are different from those of fatty acid degradation. Nevertheless, both processes may involve the same, although not exchangeable, intermediates. Acetyl-CoA forms the building blocks of the newly synthesized fatty acid. It may be derived from glucose, amino acids, or ethanol. 

The biosynthesis of optically active TIQs, exemplified by the presence of ( )-salsolinol in human fluids (189b), requires some comment. This is particularly warranted since many investigators have concluded that the conversion of dopamine to TIQ 64b is the result of condensation of the amine with acetaldehyde originating directly from ethanol. As shown in Fig. 32, this reaction, when carried out in vitro, affords racemic salsolinol (64) (5a,10). Formation of optically active TIQ 64b from dopamine and acetaldehyde would require that the Pictet-Spengler reaction be enzymatically controlled, as observed in the condensation of dopamine with 4-hydroxyphenylacetaldehyde in benzylisoquinoline-producing plants (209). The enzyme required to perform this reaction in mammalian systems has not yet been found. There are several observations which dispute such a reaction taking place in mammals the finding of 1-carboxy-TIQ 91 and DIQ 69 as major metabolites (189) and the very low levels of acetaldehyde detected in the brains of animals after alcohol consumption (215,216). This makes the acetaldehyde route to optically active 1-methyl-substituted TIQ suspect. 

Lycopene synthesis in the rin mutant was enhanced by high 02 in the presence of 10 ppm ethylene (Frenkel and Garrison, 1976). On the other hand, ethanol inhibits ripening and the synthesis of tomato lycopene (Saltveit and Mencarelli, 1988). In addition, Sheehy et al. (1988) found that a reduction in polygalacturonase did not affect biosynthesis of lycopene. Lampe and Watada (1971) and Mohr (1979) pointed out that the lycopene content in tomato fruits may be increased by improving the practices at times of selection of varieties, fertilization and harvest. 

After biosynthesis of the polyester and separation of the bacterial biomass from the supernatant, the required recovery process (typically a solid-liquid extractiOTi procedure) can constitute another not negligible cost factor, especially in large-scale production. Here extraction solvents that can easily be recycled will be of interest [53]. In order not to leave the patterns of sustainability in biopolymer production, it will be indispensable to concentrate the development of new extraction processes on such recyclable solvents that are also of environmentally sound nature [54], Typical harmful chlorinated solvents like chloroform must be avoided. A PHB production process embedded in an ethanol production plant has the advantage to utilise the medium chain length alcohol fraction (fusel alcohols) from the distillery step, consisting mainly of iso-pentanol. The application of the fusel alcohols as extracting solvents unites two important points On the one hand, this liquid normally constitutes a surplus product that has little market value. When used as an extraction solvent the costs for alternative solvents are saved. Furthermore, this extraction solvent is less harmful to handle than the classical extraction solvent chloroform [27],... 

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