Learning Objectives
Distinguish between NAD+ and NADP+ based on their metabolic roles. Identify the vitamin precursors for nicotinamide and flavin nucleotides. Categorize the major biochemical pathways utilizing NADPH.
1. Electron Carrier Precursors
Universal electron acceptors are coenzymes derived from B vitamins that facilitate the transfer of reducing equivalents (electrons and protons) in redox reactions.
- Nicotinamides (NAD+, NADP+): Derived from Vitamin B3 (Niacin).
- Flavins (FAD, FMN): Derived from Vitamin B2 (Riboflavin).
Biochemical Correlation: Catabolism vs. Anabolism
NAD+ is used primarily in catabolic processes (breakdown) to carry reducing equivalents away to the electron transport chain as NADH. Conversely, NADPH is used in anabolic processes (synthesis) as a source of reducing equivalents to build complex molecules.
2. The Multi-Faceted Roles of NADPH
Produced primarily via the HMP Shunt (Pentose Phosphate Pathway), NADPH is a critical cofactor for several protective and synthetic systems.
| System | Role of NADPH |
|---|---|
| Anabolic Synthesis | Provides power for steroid and fatty acid synthesis. |
| Respiratory Burst | Used by NADPH oxidase in phagocytes to kill bacteria. |
| P-450 System | Essential for the detoxification of drugs and toxins in the liver. |
| Glutathione Reductase | Maintains reduced glutathione to neutralize free radicals. |
Clinical Correlate: CGD
In Chronic Granulomatous Disease (CGD), a deficiency of NADPH oxidase prevents the respiratory burst. Patients experience recurrent infections with catalase-positive organisms (e.g., S. aureus, Aspergillus) because they cannot generate reactive oxygen species despite having NADPH.
Activity