C1 Transfer + Methionine + Trans-Sulfuration Cycle (Simple Recall Diagram)
SERINE
│
(SHMT + Vitamin B6/PLP)
│
▼
THF ───► METHYLENE-THF
│
┌───────────┴───────────┐
│ │
│ │
▼ ▼
DNA SYNTHESIS METHYL-THF
dUMP → dTMP │
│
(Methionine Synthase
+ Vitamin B12)
│
▼
HOMOCYSTEINE
│
▼
METHIONINE
│
(+ ATP)
▼
SAM
(Universal methyl donor)
│
methylation reactions
│
▼
SAH
│
▼
HOMOCYSTEINE
│
┌──────────────────┴──────────────────┐
│ │
│ │
▼ ▼
Back to Methionine TRANS-SULFURATION
(B12 + methyl-THF) │
│
(CBS + Vitamin B6)
│
▼
CYSTATHIONINE
│
(Cystathionase + B6)
│
▼
CYSTEINE + α-KETOBUTYRATE
│
▼
Propionyl-CoA
│
▼
TCA cycle
Vitamins to Remember
Vitamin | Main Role |
|---|---|
B9 (Folate) | THF/C1 carrier |
B12 | Homocysteine → Methionine |
B6 (PLP) | SHMT + trans-sulfuration |
B2 (FAD) | MTHFR cofactor |
High-Yield Clinical Associations
Problem | Cause |
|---|---|
Megaloblastic anemia | Folate or B12 deficiency |
Methyl-folate trap | B12 deficiency |
↑ Homocysteine | B6, B9, B12 deficiency |
Homocystinuria | CBS deficiency |
Neural tube defects | Folate deficiency |
Neurologic defects | B12 deficiency |