## Thiamine and Transketolase **Key Point:** Thiamine (vitamin B₁) is converted to its active form, thiamine pyrophosphate (TPP), which is an essential coenzyme for transketolase — a critical enzyme in the pentose phosphate pathway. ## Role of TPP in Carbohydrate Metabolism Transketolase catalyzes the transfer of two-carbon ketol groups from ketose phosphates to aldose phosphates. This reaction is fundamental to: - The non-oxidative phase of the pentose phosphate pathway - Generation of NADPH (reducing power for biosynthesis) - Production of ribose-5-phosphate (nucleotide synthesis) ## B Vitamin Coenzyme Functions — Comparison Table | Vitamin | Active Form | Primary Enzyme/Pathway | Key Function | | --- | --- | --- | --- | | Thiamine (B₁) | TPP | Transketolase, pyruvate dehydrogenase | 1-carbon & ketol transfer | | Riboflavin (B₂) | FAD/FADH₂ | Electron transport chain, oxidative enzymes | Redox reactions | | Niacin (B₃) | NAD⁺/NADH | Glycolysis, TCA cycle, dehydrogenases | Hydride transfer | | Pyridoxine (B₆) | PLP | Transamination, decarboxylation | Amino acid metabolism | **High-Yield:** TPP deficiency causes Wernicke–Korsakoff syndrome (acute neurological emergency in alcoholics) and beriberi (peripheral neuropathy and cardiac dysfunction). **Clinical Pearl:** Transketolase activity is used as a functional marker of thiamine status — decreased activity in red blood cells indicates deficiency.
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