Methylcrotonyl-CoA carboxylase

Methylcrotonyl-CoA carboxylase
methylcrotonoyl-Coenzyme A carboxylase 1 (alpha)
Symbol MCCC1
Entrez 56922
HUGO 6936
OMIM 609010
RefSeq NM_020166
UniProt Q96RQ3
Other data
EC number
Locus Chr. 3 q27.1
methylcrotonoyl-Coenzyme A carboxylase 2 (beta)
Symbol MCCC2
Entrez 64087
HUGO 6937
OMIM 609014
RefSeq NM_022132
UniProt Q9HCC0
Other data
EC number
Locus Chr. 5 q12-q13

Methylcrotonyl CoA carboxylase (MCC) (3-Methylcrotonyl CoA carboxylase, methylcrotonoyl-CoA carboxylase) is a biotin-requiring enzyme located in the mitochondria. MCC uses bicarbonate as a carboxyl group source to catalyze the carboxylation of a carbon adjacent to a carbonyl group performing the 4th step in processing leucine, an essential amino acid.[1]



During branched-chain amino acid degradation, MCC performs a single step in the breakdown of leucine to eventually yield acetyl CoA and acetoacetate.[2] MCC catalyzes the carboxylation of 3-methylcrotonyl CoA to 3-methylglutaconyl CoA. 3-Methylglutaconyl CoA is then hydrated to produce 3-hydroxy-3-methylglutaryl CoA. 3-Hydroxy-3-methylglutaryl CoA is cleaved into two molecules, acetoacetate and acetyl CoA.

Point mutations and deletion events in the genes coding for MCC can lead to MCC deficiency, an inborn error of metabolism which usually presents with vomiting, metabolic acidosis, very low plasma glucose concentration, and very low levels of carnitine in plasma.[3]


Bicarbonate is activated by the addition of ATP, increasing the reactivity of bicarbonate. Once bicarbonate is activated, the biotin portion of MCC performs nucleophilic attack on the activated bicarbonate to form enzyme-bound carboxybiotin. The carboxybiotin portion of MCC can then undergo nucleophilic attack transferring the carboxyl group to the substrate, 3-methylcrotonyl CoA, to form 3-methylglutaconyl CoA.[4]


MCC is not regulated by small molecules or dietary or hormonal factors.[5]


  1. ^ Bruice, Paula Y. Organic Chemistry. New Jersey: Prentice Hall, 2001. 1010-1011.
  2. ^ Berg, Jeremy M., John L. Tymoczko, Lubert Stryer. Biochemistry. New York: Freeman, 2002. 652-653.
  3. ^ Stipanuk, Martha H. Biochemical and Physiological Aspects of Human Nutrition. New York: Saunders, 2000. 535-536.
  4. ^ Berg, Jeremy M., John L. Tymoczko, Lubert Stryer. Biochemistry. New York: Freeman, 2002. 652-653.
  5. ^ Stipanuk, Martha H. Biochemical and Physiological Aspects of Human Nutrition. New York: Saunders, 2000. 535-536.

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