In enzymology, a cyanocobalamin reductase (cyanide-eliminating) () is an enzyme that catalyzes the chemical reaction
The 3 substrates of this enzyme are cob(I)alamin, cyanide, and NADP<sup>+</sup>, whereas its 3 products are cyanocob(III)alamin, NADPH, and H<sup>+</sup>.
This enzyme belongs to the family of oxidoreductases, specifically those that oxidize metal ions and use NAD+ or NADP+ as an electron acceptor (for that oxidization reaction). The systematic name of this enzyme class is cob(I)alamin, cyanide:NADP+ oxidoreductase. Other names in common use include cyanocobalamin reductase, cyanocobalamin reductase (NADPH, cyanide-eliminating), cyanocobalamin reductase (NADPH, CN-eliminating), and NADPH:cyanocob(III)alamin oxidoreductase (cyanide-eliminating). This enzyme participates in porphyrin and chlorophyll metabolism. It uses one cofactor, FAD.
Humans have one gene producing a protein with this enzymatic activity, MMACHC. This enzyme also has alkylcobalamin reductase activity.