Methylmalonic aciduria and homocystinuria type C protein (MMACHC) is a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
that in humans is encoded by the ''MMACHC''
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
.
Function
The C-terminal region of the product of the MMACHC gene is similar to TonB, a bacterial protein involved in energy transduction for
cobalamin
Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. It is one of eight B vitamins. It is required by animals, which use it as a cofactor in DNA synthesis, in both fatty acid and amino acid metabolism. It ...
uptake.
The MMACHC gene product catalyzes the
decyanation of
cyanocobalamin
Cyanocobalamin is a form of vitamin used to treat vitamin deficiency except in the presence of cyanide toxicity. The deficiency may occur in pernicious anemia, following surgical removal of the stomach, with fish tapeworm, or due to bowel ...
as well as the
dealkylation
Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effecting al ...
of alkylcobalamins including
methylcobalamin
Methylcobalamin (mecobalamin, MeCbl, or MeB) is a cobalamin, a form of vitamin B. It differs from cyanocobalamin in that the cyano group at the cobalt is replaced with a methyl group. Methylcobalamin features an octahedral cobalt(III) centre and c ...
and
adenosylcobalamin
Adenosylcobalamin (AdoCbl), also known as coenzyme B12, cobamamide, and dibencozide, is, along with methylcobalamin (MeCbl), one of the biologically active forms of vitamin B12.
Adenosylcobalamin participates as a cofactor in radical-mediated 1,2 ...
. This function has also been attributed to
cobalamin reductases. The MMACHC gene product and cobalamin reductases enable the interconversion of cyano- and alkylcobalamins.
[Quadros, EV]
"Advances in the Understanding of Cobalamin Assimilation and Metabolism"
''Br J Haematol''. 2010 Jan; 148(2): 195–204.
Clinical significance
Mutations are associated with
methylmalonic acidemia
Methylmalonic acidemia, also called methylmalonic aciduria, is an autosomal recessive metabolic disorder that disrupts normal amino acid metabolism. It is a classical type of organic acidemia. The result of this condition is the inability to proper ...
.
References
Further reading
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External links
GeneReviews/NCBI/NIH/UW entry on Disorders of Intracellular Cobalamin Metabolism
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