Fructose bacteria

When sorbitol is administered intravenously, it is converted to fructose rather than to glucose. It is poorly absorbed in the small intestine, and much is fermented by colonic bacteria to short-chain fatty acids, CO2, and Hj, leading to abdominal pain and diarrhea (sorbitol intolerance). 

In an fermentation process of a solution containing sucrose, the enzyme in-vertase, present in yeast, acts as a catalyst to convert sucrose into a 1 1 mixture of glucose and fructose. Thus, sucrose is a disaccharide that hydrolyzes in the presence of certain bacteria to yield glucose and fructose. The ether linkage in sucrose is broken to yield two alcohols ... 

In view of its importance, reductive dissolution of Fe oxides has been widely studied. Reductants investigated include dithionite, thioglycolic acid, thiocyanate, hydrazine, ascorbic acid, hydroquinone, H2S, H2, Fe ", tris (picolinato) V", fulvic acid, fructose, sucrose and biomass/bacteria (Tab. 12.3). Under the appropriate conditions, reductive dissolution may also be effected photochemically. As with protonation, the extent of reduction may be strongly influenced by ligand and proton adsorption on the oxide surface. 

From the many enzymes that are known to make and break C-C bonds, we first chose the two transferases, transketolase (TKT) and transaldolase (TAL), both from the Gram-negative bacterium Escherichia coli. While project B21 evolved, we learned that this microorganism holds other and so far unknown enzymes which are of interest for asymmetric syntheses. One transketolase-like enzyme, 1-deoxy-D-xylulose 5-phosphate synthase (DXS), turned out to be the first enzyme of a novel biosynthetic pathway leading to isoprenoids in bacteria, algae, and plants. The other, fructose 6-phosphate aldolase (ESA) - while similar to transaldolase - allows the direct use of the inexpensive dihydroxyacetone in aldol condensations. 

The metabolism of anaerobic chytrids has not been studied in great detail, but it is known that most anaerobic chytrids studied so far produce formate, acetate, succinate, lactate and ethanol besides hydrogen and carbon dioxide when growing on cellulose, glucose or fructose as a carbon source (Julliand et al. 1998). Such a mixed acid fermentation is very similar to bacterial mixed acid fermentations that are, for example, well known for facultative anaerobic enteric bacteria, such as Escherichia coli. 

Some bacteria and protists and perhaps all plants have a phosphofructokinase that uses pyrophosphate (PPi), not ATP, as the phosphoryl group donor in the synthesis of fructose 1,6-bisphosphate ... 

These enzymes have been found in all plant and animal tissues examined and are absent only from a few specialized bacteria. Three closely related isoenzymes are found in vertebrates.185 186 The much studied rabbit muscle aldolase A is a 158-kDa protein tetramer of identical peptide chains.186 187 Aldolase B, which is lacking in hereditary fructose intolerance, predominates in liver and isoenzyme C in brain.185... 

Some lactic acid bacteria of the genus Lactobacillus, as well as Leuconostoc mesenteroides and Zymomonas mobilis, carry out the heterolactic fermentation (Eq. 17-33) which is based on the reactions of the pentose phosphate pathway. These organisms lack aldolase, the key enzyme necessary for cleavage of fructose 1,6-bisphosphate to the triose phosphates. Glucose is converted to ribulose 5-P using the oxidative reactions of the pentose phosphate pathway. The ribulose-phosphate is cleaved by phosphoketolase (Eq. 14-23) to acetyl-phosphate and glyceraldehyde 3-phosphate, which are converted to ethanol and lactate, respectively. The overall yield is only one ATP per glucose fermented. 

In bacteria, which lack formate dehydrogenase, formaldehyde can be oxidized to C02 to provide energy beginning with the reactions of Eq. 17-51. The resulting fructose 6-P is isomerized to glucose 6-P, which is then dehydrogenated via Eq. 17-12 to form C02 and the regenerating substrate ribulose 5-phosphate. 

In bacteria this enzyme is usually inhibited by AMP and ADP and activated by glycolytic intermediates such as fructose 1,6-P2, fructose 6-P, or pyruvate. In higher plants, green algae, and cyanobacteria the enzyme is usually activated by 3-phosphoglycerate, a product of photosynthetic C02 fixation, and is inhibited by inorganic phosphate (Pj).106 108. 

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