Pentose phosphate pathway control

Johansson, B., Hahn-Gaegerdal, B. (2002). The non-oxidative pentose phosphate pathway controls the fermentation rate of xylulose, but not of xylose in Saccharomyces cerevisiae. FEMS Yeast Research, 2, 211 282. 

The transketolase and transaldolase reactions are reversible and so allow either the conversion of ribose 5-phosphate into glycolytic intermediates when it is not needed for other cellular reactions, or the generation of ribose 5-phosphate from glycolytic intermediates when more is required. The rate of the pentose phosphate pathway is controlled by NADP+ regulation of the first step, catalyzed by glucose 6-phosphate dehydrogenase. 

Berthon HA, Kuchel PW, and Nixon PE (1992) High control coefficient of transketolase in the nonoxidative pentose phosphate pathway ofhuman erythrocytes NMR, antibody, and computer simulation studies. Biochemistry 31,12792-8. 

The Rate of the Pentose Phosphate Pathway Is Controlled by the Level of NADP... 

Oxygen limitation had little effect on the activities of TAL and TKL. When OTR varied from 0 to 12.6 mmol/L-h, TAL and TKL aetivities always maintained at low levels (Fig. 4c). TAL and TKL activities always maintained at low levels, to show big control effects on xylose metabolism. Walfi idsson et al. [34] overexpressed TAL in XR- and XDH-expressing S. cerevisiae, whieh increased the cell growth but not ethanol production. Karhumaa et al. [30] found that increased XR and XDH activities redirected the production from xylitol to ethanol, whereas the rate of xylose consumption was governed by the overexpressed nonoxidative pentose phosphate pathway. 

The entry of glucose 6-phosphate into the pentose phosphate pathway is controlled by the cellular concentration of NADPH. NADPH is a strong product inhibitor of glucose 6-phosphate dehydrogenase, the first enzyme of the pathway. As NADPH is oxidized in other pathways, the product inhibition of glucose 6-phosphate dehydrogenase is relieved, and the rate of the enzyme is accelerated to produce more NADPH. 

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