# HMP Shunt (Pentose Phosphate Pathway)

The **HMP Shunt**, also known as the **Pentose Phosphate Pathway** or the Phosphogluconate Pathway, is a biochemical pathway that serves as an alternative metabolic pathway for glucose.

The first phase is **oxidative** and **irreversible**. **Glucose-6-phosphate (G6P)** is converted via a series of steps into **Ribulose-5-phosphate**. The most important catalytic enzyme is **Glucose-6-phosphate Dehydrogenase (G6PD)**, which **produces NADPH** in the process. This is the major source of NADPH in the cell, and decreased NADPH can be seen in [**G6PD Deficiency**](/content/view/4868/index.html).

The second phase is non-oxidative and reversible, and involves **transketolase** as a major enzyme. **Ribulose-5-phosphate** is converted into **Ribose-5-phosphate**, which can undergo further reactions to produce Fructose-6-phosphate and Glyceraldehyde-3-phosphate. Ribose-5-phosphate is an important precursor to PRPP in the [**Purine**](/content/view/4386/index.html) and [**Pyrimidine Synthesis**](/content/view/4541/index.html) pathways. Of note, the action of transketolase requires [**Vitamin B1/Thiamine**](/content/view/3680/index.html) as a cofactor.