While enzyme assays show that levels of glucose-1-P adenelylytransferase and CFTRinh-172 glycogen synthase increase with decreasing growth rate during transition to stationary phase in most organisms [71], catalytic activities of these enzymes, SC79 as well as α-glucan phosphorylase activity, increased with higher growth rates

in C. cellulolyticum[73]. Furthermore, in contrast to many bacterial species, which produce glycogen during the onset of stationary phase, glycogen synthesis reached a maximum in exponential phase and was utilized during transition to stationary phase in batch C. cellulolyticum cultures [73]. Interestingly, expression of α-glucan phosphorylase also increased 2.5-fold, which may help the cell utilize glycogen in the absence of an external carbon source. Pentose phosphate SBI-0206965 order pathway The oxidative branch of the pentose phosphate pathway (PPP) generates reducing equivalents (NADPH) for biosynthesis, whereas the non-oxidative branch produces key intermediates, namely ribose-5-P and erythrose-4-P,

required for the synthesis of nucleotides and aromatic amino acids, respectively. The absence of genes encoding glucose-6-P dehydrogenase, gluconolactonase, and 6-P-gluconate dehydrogenase of the oxidative PPP branch suggests that an alternative NADPH generation system must exist and that glycolytic intermediates (glyceraldehydes-3-phosphate and fructose-6-phosphate) must feed the non-oxidative branch of the PPP (Figure  2c. Additional file 4). Furthermore, homology-based annotation suggests that

the non-oxidative branch of the PPP is incomplete. While C. thermocellum encodes ribulose-5-P isomerase, ribulose-5-P epimerase, and two transketolases (Cthe_2443-2444 and Cthe_2704-2705), no gene encoding a transaldolase has been identified. 2D-HPLC-MS/MS expression profiles reveal that transketolase Cthe_2704-2705 is highly expressed throughout fermentation (RAI ~ 0.7), while Cthe_2443 is not detected and Cthe_2444 is found only in low amounts (RAI = 0.09). While ribose-5-P isomerase was detected (RAI = 0.37), ribose-5-P epimerase was not. Given the absence of transaldolase, 17-DMAG (Alvespimycin) HCl ribose-5-phosphate must be synthesized using an alternative pathway. A novel mechanism of non-oxidative hexose-to-pentose conversion that does not require transaldolase has been demonstrated in Entamoeba histolytica and other parasitic protists [75–77]. This system employs transketolase, aldolase, and PPi-dependent 6-phosphofructokinase (Figure  2c). Susskind et al. have shown that fructose-1,6-bisphosphate aldolase, which typically converts glyceraldehyde-3-P and dihydroxyacetone-P into fructose-1,6-bisphosphate, is capable of converting dihydroxyacetone-P and erythrose-4-P into sedoheptulose-1,7-bisphosphate [77].