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The modulation of the oxidative phase of the pentose phosphate pathway in mouse liver
P Velasco1, A M Sieiro, I Ibarguren
1Departamento de Bioquímica y Biología Molecular, Universidad de Santiago de Compostela, Facultad de Veterinaria, Lugo, Spain.
Abstract:
The glucose-6-phosphate dehydrogenase from mouse liver is fully inhibited in vitro by physiological concentrations of NADPH. This suggests that the oxidative phase of the pentose phosphate pathway requires some deinhibitory system. In order to investigate regulation of the pentose phosphate pathway, various parameters (intermediate concentrations, mass-action ratios of reactions, etc.) were measured in liver from control mice and from meal-fed mice. Assays were also carried out to detect any molecules causing the reverse of glucose-6-phosphate dehydrogenase inhibition by NADPH. The liver of meal-fed mice show greater glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities. They also had greater concentrations of several metabolic intermediates and triglycerides than the control animals (P < 0.001). These results prove that the diet increases the flow of the pentose phosphate pathway in a lipogenic sense. The glutathione reductase does not change with the diet, suggesting that this enzyme does not participate in the modulating process. Unlike rat liver, no molecules causing the reverse of glucose-6-phosphate dehydrogenase inhibition by NADPH were detected. These data suggest that the increase of flow of the pentose phosphate pathway during lipogenesis is obtained by an increase in enzyme synthesis.
Insights
Meal-fed mice show increased pentose phosphate pathway activity, particularly in lipogenesis. This enhanced flux is likely due to increased enzyme synthesis, not regulatory molecules, in mouse liver.
Area of Science:
- Biochemistry
- Metabolic Regulation
- Molecular Biology
Background:
- Glucose-6-phosphate dehydrogenase (G6PD) in mouse liver is inhibited by NADPH.
- This inhibition suggests a need for a deinhibitory system to regulate the pentose phosphate pathway (PPP).
Purpose of the Study:
- To investigate the regulation of the pentose phosphate pathway in mouse liver.
- To identify potential molecules that reverse NADPH inhibition of G6PD.
- To understand how diet influences PPP flux and lipogenesis.
Main Methods:
- Measurement of metabolic intermediates and enzyme activities (G6PD, 6-phosphogluconate dehydrogenase, glutathione reductase) in control and meal-fed mice.
- Assays for molecules reversing NADPH inhibition of G6PD.
- Analysis of mass-action ratios of PPP reactions.
Main Results:
- Meal-fed mice exhibited higher G6PD and 6-phosphogluconate dehydrogenase activities.
- Increased concentrations of metabolic intermediates and triglycerides were observed in meal-fed mice.
- No molecules reversing NADPH inhibition of G6PD were detected in mouse liver, unlike in rat liver.
Conclusions:
- Diet significantly increases pentose phosphate pathway flux towards lipogenesis in mouse liver.
- The observed increase in PPP flux is primarily mediated by enhanced enzyme synthesis.
- Glutathione reductase does not appear to be involved in the dietary modulation of the PPP.