The cellular uptake and conversion of exogenous B12 (cyanocobalamin) to biologically active cofactors (adenosylcobalamin and methylcobalamin) in mammalian cells requires the enzymatic activity of CblC, also known as MMACHC (for methylmalonic aciduria (cobalamin deficiency) cblC type, with homocystinuria) [51]. Here, CBLC is linked to homocystinuria.