Pentose phosphate pathway
Template:Infobox metabolic pathway
The pentose phosphate pathway (PPP), also known as the phosphogluconate pathway and the hexose monophosphate shunt, is a metabolic pathway parallel to glycolysis. It generates NADPH and pentoses (5-carbon sugars) as well as ribose 5-phosphate, a precursor for the synthesis of nucleotides. While it does not produce ATP, it is crucial for anabolic reactions and antioxidant defense.
Overview[edit]
The pentose phosphate pathway consists of two distinct phases: the oxidative phase and the non-oxidative phase.
Oxidative Phase[edit]
In the oxidative phase, glucose-6-phosphate is oxidized to produce NADPH and ribulose 5-phosphate. The key enzyme in this phase is glucose-6-phosphate dehydrogenase (G6PD), which catalyzes the first step and is a major control point of the pathway.
Non-Oxidative Phase[edit]
The non-oxidative phase involves the interconversion of sugars. Ribulose 5-phosphate is converted into ribose 5-phosphate and other sugars such as xylulose 5-phosphate. These sugars can then enter glycolysis or be used in the synthesis of nucleotides and nucleic acids.
Functions[edit]
The pentose phosphate pathway serves several critical functions:
- **NADPH Production**: NADPH is essential for biosynthetic reactions, including fatty acid synthesis and cholesterol synthesis, and for maintaining the reduced glutathione pool in cells.
- **Ribose 5-Phosphate Production**: This sugar is a precursor for the synthesis of nucleotides and nucleic acids.
- **Metabolic Flexibility**: The pathway provides a means to metabolize pentoses and to interconvert sugars for various biosynthetic needs.
Regulation[edit]
The pentose phosphate pathway is primarily regulated at the level of glucose-6-phosphate dehydrogenase. The activity of G6PD is influenced by the cellular levels of NADP+ and NADPH. High levels of NADPH inhibit the enzyme, while high levels of NADP+ activate it.
Clinical Significance[edit]
Deficiencies in glucose-6-phosphate dehydrogenase can lead to G6PD deficiency, a genetic disorder that affects red blood cells and can result in hemolytic anemia. This condition is often triggered by certain foods, infections, or medications.
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