A PPP enzyme refers to an enzyme involved in the Pentose Phosphate Pathway (PPP), a metabolic pathway parallel to glycolysis. This pathway's primary purpose is not to produce energy but to generate reducing equivalents in the form of NADPH, as well as the precursor metabolite, ribose-5-phosphate.
Key PPP Enzyme
The reference highlights the first enzyme in this crucial pathway:
- Glucose-6-phosphate dehydrogenase (G6PDH): This is the starting enzyme in the PPP. It catalyzes the conversion of glucose-6-phosphate to 6-phosphoglucono-δ-lactone, producing NADPH in the process.
Importance of PPP Enzymes
These enzymes play vital roles by:
- Generating NADPH: This is critical for various cellular processes:
- Lipogenesis: NADPH is essential for the synthesis of fatty acids.
- Glutathione Regeneration: NADPH is required by glutathione reductase to maintain reduced glutathione, which protects against oxidative damage.
- Producing Ribose-5-Phosphate: This sugar is a building block for nucleotides and nucleic acids, crucial for cell growth and DNA synthesis.
Table of Core Enzymes in the Pentose Phosphate Pathway
| Enzyme Name | Reaction Catalyzed | Primary Product |
|---|---|---|
| Glucose-6-phosphate dehydrogenase (G6PDH) | Glucose-6-phosphate to 6-phosphoglucono-δ-lactone | NADPH |
| 6-phosphogluconolactonase | 6-phosphoglucono-δ-lactone to 6-phosphogluconate | N/A |
| 6-phosphogluconate dehydrogenase | 6-phosphogluconate to Ribulose-5-phosphate | NADPH |
| Ribulose-5-phosphate isomerase | Ribulose-5-phosphate to Ribose-5-phosphate | N/A |
| Transketolase | Transfer of two-carbon units | Various sugars |
| Transaldolase | Transfer of three-carbon units | Various sugars |
G6PDH Deficiency
- Deficiency in G6PDH can cause hemolytic anemia as the cells are less able to deal with oxidative stress, as mentioned in the reference.
In summary, PPP enzymes, particularly G6PDH, are critical for the production of NADPH and ribose-5-phosphate, essential for various cellular functions such as fatty acid synthesis, protection against oxidative damage and nucleotide synthesis.
