Fermentation phosphogluconate pathway

The study of these metabolic steps is quite active at the present time. As noted above, Dickens found that ribose-5-phosphate was fermented anaerobically to ethanol, a 2-carbon compound, inorganic phosphate, and CO2. Racker observed that extracts of E. colt converted ribose-5-phosphate to a triose phosphate, which could be analyzed in the presence of triose phosphate isomerase as dihydroxyacetone phosphate.Therefore, the products of the oxidative pathway eventually join the Embden-Meyerhof scheme at the triose phosphate stage, the major difference being the formation of 2 moles of triose phosphate in the latter pathway and only 1 mole via the phosphogluconate pathway. 

Thus we find an organism, Leuconostoc mesenteroides, which can only ferment glucose by the way of phosphogluconate because of the presence of only the enzymes of the phosphogluconate pathway. Conversely, it has already been noted that muscle is low in the dehydrogenases of this system, and it might be anticipated that this tissue would reveal the use of glucose predominantly by the Embden-Meyerhof scheme. 

Many LAB are able to ferment pentoses. They can only ferment heterofermen-tatively by entering the phosphogluconate pathway as either ribulose-5 phosphate or xylulose-5 phosphate (Kandler 1983) (Fig. 4). Pentoses (such as arabinose, ribose, xylose) are converted into lactate and acetate CO2 is not produced. The sum of the equation is... 

Obligately heterofermentative Ferment both hexoses and pentoses by the 6-PG/PK (6-phosphogluconate/phosphoketolase pathway) and produce lactic acid, ethanol/acetic acid, and CO2 (this latter only from hexoses) in the ratio 1 1 1... 

Dickens also observed the oxidation and fermentation by yeast systems of n-ribose-5-phosphate, but not of the expected degradation product of 6-phosphogluconate, n-arabinose-5-phosphate. He proposed that ribose arose in some manner from phosphogluconate degradation and formulated the reaction scheme of the oxidative pathway of glucose-6-phosphate shown in Fig. 12. 

Heterolactic fermentation pathway of glucose (6-phosphogluconate/phosphoketolase pathway]... 

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