(AdoCbl) is required by methylmalonyl-CoA mutase, which catalyzes the conversion of L- methylmalonyl-CoA to succinyl-CoA.
The generation of methionine from homocysteine requires cytoplasmic methylcobalamin and the conversion of methyl-malonyl-coenzyme A to succinyl-coenzyme A requires mitochondrial 5-deoxyadenosylcobalamin
The biologically active coenzyme forms of vitamin B12 that play a role in human metabolism are methylcobalamin and 5-deoxyadenosylcobalamin
(commonly known as adenosylcobalamin).
The basis of an elevated MMA concentration as a sensitive functional indicator of vitamin [B.sub.12] deficiency is that 5-deoxyadenosylcobalamin
is an essential cofactor for the conversion of methylmalonyl-CoA to succinyl-CoA.
MMA is caused by a defect in the conversion of L-methylmalonyl-CoA to succinyl-CoA, catalyzed by the enzyme methylmalonylCoA (MMCoA) mutase (EC.220.127.116.11), which requires 5-deoxyadenosylcobalamin
(AdoCbl) as a cofactor.