Methylmalonic aciduria and homocystinuria type C protein (MMACHC) is a protein that in humans is encoded by the MMACHC gene. 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 uptake. The MMACHC gene product catalyzes the decyanation of cyanocobalamin as well as the dealkylation of alkylcobalamins including methylcobalamin and adenosylcobalamin. This function has also been attributed to cobalamin reductases. The MMACHC gene product and cobalamin reductases enable the interconversion of cyano- and alkylcobalamins. Clinical significance Mutations are associated with methylmalonic acidemia. References Further reading External links GeneReviews/NCBI/NIH/UW entry on Disorders of Intracellular Cobalamin Metabolism