Table 1: Fatty Acid and Triglyceride Metabolism
| Vitamin | Impaired Reaction | Enzyme Affected | Consequence |
| Riboflavin (B2) | β-oxidation of fatty acids | Acyl-CoA dehydrogenase | Reduced ATP production from fats |
| Niacin (B3) | β-oxidation of fatty acids | Hydroxyacyl-CoA dehydrogenase | Energy generation from fats reduced |
| Triglyceride synthesis | Glycerol-3-phosphate dehydrogenase | Impaired triglyceride formation | |
| Biotin | Fatty acid synthesis | Acetyl-CoA carboxylase | Disrupted synthesis of fatty acids |
| Odd-chain fatty acid metabolism | Propionyl-CoA carboxylase | Accumulation of toxic intermediates | |
| Vitamin B12 | Odd-chain fatty acid metabolism | Methylmalonyl-CoA mutase | Impaired odd-chain fatty acid breakdown |
| Vitamin B6 (PLP) | Essential fatty acid metabolism | Δ6-Desaturase | Reduced production of essential fatty acids |
Key Reactions Explained:
- β-Oxidation (Riboflavin, Niacin):
- Acyl-CoA dehydrogenase: FAD-dependent step in β-oxidation of fatty acids.
- Hydroxyacyl-CoA dehydrogenase: NAD-dependent step in the oxidation of fatty acids.
- Fatty Acid Synthesis (Biotin):
- Acetyl-CoA carboxylase: Initiates fatty acid synthesis by forming malonyl-CoA
- Triglyceride Synthesis (Niacin):
- Glycerol-3-phosphate dehydrogenase: Converts DHAP to glycerol-3-phosphate for triglyceride assembly.
- Odd-Chain Fatty Acid Metabolism (Biotin, Vitamin B12):
- Biotin-dependent Propionyl-CoA carboxylase produces methylmalonyl-CoA.
- Vitamin B12-dependent methylmalonyl-CoA mutase converts methylmalonyl-CoA to succinyl-CoA for TCA cycle entry.
Table 2: Vitamin Deficiencies and Impairments in Nucleotide Metabolism
| Vitamin | Impaired Reaction | Enzyme Affected | Consequence |
| Folate (B9) | Synthesis of thymidylate (dTMP) from dUMP | Thymidylate synthase (via 5,10-Methylene-THF) | Impaired DNA synthesis, megaloblastic anemia |
| Purine synthesis | Formyltransferases | Reduced nucleotide production | |
| Vitamin B12 | Conversion of homocysteine to methionine | Methionine synthase | Disrupted folate recycling, impaired DNA synthesis |
| Riboflavin (B2) | Regeneration of thioredoxin for ribonucleotide reduction | Thioredoxin reductase (FAD-dependent) | Indirectly impaired DNA replication and repair due to lack of deoxyribonucleotide production |
| Thiamine (B1) | Pentose phosphate pathway for ribose-5-phosphate synthesis | Transketolase | Reduced availability of ribose for nucleotide synthesis |
| Pyridoxine (B6) | Synthesis of purines from glycine and formate | Enzymes involved in one-carbon metabolism | Disrupted purine synthesis |
Key Reactions Explained:
- Folate (B9):
- Thymidylate synthesis: Converts dUMP to dTMP for DNA synthesis.
- Purine synthesis: Provides carbon units required for nucleotide bases (adenine, guanine).
- Vitamin B12:
- Supports folate recycling, essential for one-carbon transfers in nucleotide biosynthesis.
- Riboflavin (B2):
- Required for ribonucleotide reductase activity, converting ribonucleotides to deoxyribonucleotides.
- Thiamine (B1):
- Participates in the pentose phosphate pathway to generate ribose-5-phosphate, a precursor for nucleotide synthesis.
- Vitamin B6:
- Facilitates reactions in amino acid and one-carbon metabolism critical for purine ring assembly.
