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Vitamin Deficiencies and Impairments in Carbohydrate Metabolism
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- Explore how vitamin deficiencies, including Thiamine (B1), Riboflavin (B2), and Niacin (B3), disrupt carbohydrate metabolism.
- Learn about impaired reactions, enzymes, and metabolic consequences in pathways like glycolysis and the TCA cycle.
| Vitamin | Impaired Reaction | Enzyme Affected | Reaction Catalyzed | Pathway/Consequence |
| Thiamine (B1) | Conversion of pyruvate to acetyl-CoA | Pyruvate dehydrogenase (E1 component) | Pyruvate + CoA + NAD⁺ → Acetyl-CoA + NADH + CO₂ | Impaired entry of pyruvate into the TCA cycle, lactic acid buildup |
| Conversion of α-ketoglutarate to succinyl-CoA | α-Ketoglutarate dehydrogenase | α-Ketoglutarate + NAD⁺ + CoA → Succinyl-CoA + NADH + CO₂ | Reduced TCA cycle flux, energy deficit | |
| Non-oxidative phase of the pentose phosphate pathway | Transketolase | Xylulose-5-phosphate + Ribose-5-phosphate ↔ Glyceraldehyde-3-phosphate + Sedoheptulose-7-phosphate | Impaired nucleotide synthesis, disrupted PPP flux | |
| Riboflavin (B2) | Oxidation of succinate to fumarate | Succinate dehydrogenase | Succinate + FAD → Fumarate + FADH₂ | Decreased ATP synthesis (ETC complex II) |
| Niacin (B3) | Oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate | Glyceraldehyde-3-phosphate dehydrogenase | G3P + NAD⁺ → 1,3-Bisphosphoglycerate + NADH | Impaired glycolysis |
| Oxidative decarboxylation of isocitrate to α-ketoglutarate | Isocitrate dehydrogenase (NAD-dependent) | Isocitrate + NAD⁺ → α-Ketoglutarate + NADH + CO₂ | Impaired TCA cycle progression | |
| Conversion of malate to oxaloacetate | Malate dehydrogenase | Malate + NAD⁺ → Oxaloacetate + NADH | Impaired gluconeogenesis | |
| Oxidation in the pentose phosphate pathway | Glucose-6-phosphate dehydrogenase (G6PD) | Glucose-6-phosphate + NADP⁺ → 6-Phosphogluconolactone + NADPH | Impaired NADPH production for antioxidant defense | |
| Pantothenic Acid | Formation of acetyl-CoA from pyruvate | Pyruvate dehydrogenase complex (via Coenzyme A) | Pyruvate + CoA + NAD⁺ → Acetyl-CoA + NADH + CO₂ | Impaired carbohydrate oxidation |
| Biotin | Conversion of pyruvate to oxaloacetate | Pyruvate carboxylase | Pyruvate + CO₂ + ATP → Oxaloacetate + ADP + Pi | Impaired gluconeogenesis |
| Conversion of propionyl-CoA to methylmalonyl-CoA | Propionyl-CoA carboxylase | Propionyl-CoA + CO₂ + ATP → Methylmalonyl-CoA + ADP + Pi | Impaired odd-chain fatty acid catabolism, catabolism of Isoleucine, Valine, Methionine, and Threonine | |
| Vitamin B12 | Conversion of methylmalonyl-CoA to succinyl-CoA | Methylmalonyl-CoA mutase | Methylmalonyl-CoA → Succinyl-CoA | Impaired entry of odd-chain fatty acids into the TCA cycle and other AAs listed above |
| Vitamin B6 (PLP) | Glycogen breakdown (glycogenolysis) | Glycogen phosphorylase | Glycogen + Pi → Glucose-1-phosphate | Impaired mobilization of glucose from glycogen |
Structured Highlights
- Thiamine (B1):
- Impairs pyruvate to acetyl-CoA conversion, disrupting the TCA cycle.
- Enzyme: Pyruvate dehydrogenase.
- Riboflavin (B2):
- Affects succinate oxidation in the ETC (Complex II).
- Enzyme: Succinate dehydrogenase.
- Niacin (B3):
- Impairs glycolysis, gluconeogenesis, and TCA cycle processes.
- Enzymes: Glyceraldehyde-3-phosphate dehydrogenase, Isocitrate dehydrogenase, Malate dehydrogenase.
- Biotin:
- Essential for gluconeogenesis and odd-chain fatty acid metabolism.
- Enzymes: Pyruvate carboxylase, Propionyl-CoA carboxylase.
- Vitamin B12:
- Critical for odd-chain fatty acid and amino acid catabolism.
- Enzyme: Methylmalonyl-CoA mutase.
- Vitamin B6 (PLP):
- Affects glycogen breakdown (glycogenolysis).
- Enzyme: Glycogen phosphorylase.
