Vitamin Deficiencies and Impairments in Carbohydrate Metabolism

  • 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

  1. Thiamine (B1):
    • Impairs pyruvate to acetyl-CoA conversion, disrupting the TCA cycle.
    • Enzyme: Pyruvate dehydrogenase.
  2. Riboflavin (B2):
    • Affects succinate oxidation in the ETC (Complex II).
    • Enzyme: Succinate dehydrogenase.
  3. Niacin (B3):
    • Impairs glycolysis, gluconeogenesis, and TCA cycle processes.
    • Enzymes: Glyceraldehyde-3-phosphate dehydrogenase, Isocitrate dehydrogenase, Malate dehydrogenase.
  4. Biotin:
    • Essential for gluconeogenesis and odd-chain fatty acid metabolism.
    • Enzymes: Pyruvate carboxylase, Propionyl-CoA carboxylase.
  5. Vitamin B12:
    • Critical for odd-chain fatty acid and amino acid catabolism.
    • Enzyme: Methylmalonyl-CoA mutase.
  6. Vitamin B6 (PLP):
    • Affects glycogen breakdown (glycogenolysis).
    • Enzyme: Glycogen phosphorylase.

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