The Hexose Monophosphate (HMP) Shunt, also known as the Pentose Phosphate Pathway (PPP), is a crucial cytoplasmic pathway that supports cellular functions such as NADPH production and ribose-5-phosphate synthesis.
It is essential for biosynthetic processes and protection against oxidative stress.
HMP Shunt Pathway / Phases of the HMP Shunt
The pathway is bifurcated into two main phases: the oxidative phase, which generates NADPH, and the non-oxidative phase, which produces ribose-5-phosphate and allows for the interconversion of sugar phosphates.
1. Oxidative Phase
Glucose-6-phosphate Dehydrogenation: Converts glucose-6-phosphate to 6-phosphoglucono-δ-lactone, producing NADPH.
Lactonase Action: Converts 6-phosphoglucono-δ-lactone to 6-phosphogluconate.C.
Decarboxylation : 6-phosphogluconate is decarboxylated to ribulose-5-phosphate, generating more NADPH.
2. Non-Oxidative Phase
Interconversions: Converts ribose-5-phosphate, ribulose-5-phosphate, and xylulose-5-phosphate.
Formation of Glycolytic Intermediates: Transketolase and other enzymes convert sugar phosphates into glycolytic intermediates like fructose-6-phosphate and glyceraldehyde-3-phosphate.
Significance of the HMP Shunt
1. NADPH Production:
Supports anabolic processes like fatty acid and cholesterol synthesis.
Maintains reduced glutathione, protecting cells from oxidative stress.
2. Ribose-5-phosphate Production:
Essential for nucleotide and nucleic acid synthesis, critical for rapidly dividing cells (e.g., immune and bone marrow cells).
3. Metabolic Flexibility:
Allows cells to balance between energy production (via glycolysis) and the need for biosynthetic precursors, providing adaptability in response to metabolic demands.
This streamlined overview highlights the importance of the HMP shunt in cellular metabolism and defense against oxidative damage.