Ethanol biosynthesis

The reaction has been shown to be carried out by a pyravate decarboxylase and involves thiamine pyrophosphate in the formation of activated acetaldehyde from pyravate, which then condenses with benzaldehyde. Evidently, pyravate decarboxylase, a crucial enzyme for ethanol biosynthesis, is nsed in an urmatural way... 

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). 

Class 1 or 2, depending on the substrate used. We can see from Table 2, for example, that sucdnoglycan biosynthesis leads to a net production of ATP (Class 2) with ethanol as substrate, but the biosynthesis is energy requiring (Class 1) with glucose as substrate. 

The above observations suggested that hexoses arise in Nature by reaction of glycerose with dihydroxyacetone. A vast amount of practical information has been derived from investigation of plant- and muscle-extracts, two dissimilar systems that show many similarities in their biosynthetic manipulations. There is a close parallelism in the sequence of intermediates involved in the processes wherein D-glucose is converted to ethanol and carbon dioxide by yeasts, and to lactic acid by muscle during contraction. The importance of these schemes lies in their reversibility, which provides a means of biosynthesis from small molecules. 

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... 

Several of the B vitamins function as coenzymes or as precursors of coenzymes some of these have been mentioned previously. Nicotinamide adenine dinucleotide (NAD) which, in conjunction with the enzyme alcohol dehydrogenase, oxidizes ethanol to ethanal (Section 15-6C), also is the oxidant in the citric acid cycle (Section 20-10B). The precursor to NAD is the B vitamin, niacin or nicotinic acid (Section 23-2). Riboflavin (vitamin B2) is a precursor of flavin adenine nucleotide FAD, a coenzyme in redox processes rather like NAD (Section 15-6C). Another example of a coenzyme is pyri-doxal (vitamin B6), mentioned in connection with the deamination and decarboxylation of amino acids (Section 25-5C). Yet another is coenzyme A (CoASH), which is essential for metabolism and biosynthesis (Sections 18-8F, 20-10B, and 30-5A). 

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. 

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)... 

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