Vitamin B12 deficiency - biochemical consequences (elevated MMA, homocysteine; subacute combined degeneration)
Core concept
- B12 (cobalamin) is a cofactor for two enzymes -- deficiency biochemistry follows directly from their blockade
- Methylmalonyl-CoA mutase (methylmalonic acid -> succinyl-CoA): blocked -> inc methylmalonic acid (MMA)
- Methionine synthase (homocysteine -> methionine, using methylfolate as cofactor): blocked -> inc homocysteine AND traps folate as methyl-THF ("methylfolate trap") -> functional intracellular folate deficiency
3 more sections, plus exam facts
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