What Is 3-methylcrotonyl-CoA carboxylase

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Last updated: April 15, 2026

Quick Answer: 3-Methylcrotonyl-CoA carboxylase (MCC) is a mitochondrial enzyme complex that catalyzes the carboxylation of 3-methylcrotonyl-CoA to 3-methylglutaconyl-CoA in leucine metabolism. Deficiency affects approximately 1 in 50,000 newborns and can cause metabolic acidosis.

Key Facts

Overview

3-Methylcrotonyl-CoA carboxylase (MCC) is a biotin-dependent mitochondrial enzyme essential for the catabolism of the amino acid leucine. It functions in the fourth step of leucine degradation, ensuring toxic intermediates do not accumulate in cells.

The enzyme complex is composed of two subunits encoded by separate genes, and its proper function is critical for energy production and metabolic stability. Deficiencies can lead to organic acidemias with neurological and muscular complications.

How It Works

The enzymatic activity of MCC involves precise molecular interactions that convert a toxic intermediate into a usable metabolic product. Each component plays a defined role in substrate binding, carboxylation, and energy utilization.

Comparison at a Glance

Below is a comparison of MCC with other biotin-dependent carboxylases involved in human metabolism:

EnzymeSubstrateGene(s)Associated DisorderIncidence
3-Methylcrotonyl-CoA carboxylase3-Methylcrotonyl-CoAMCCC1, MCCC2MCC deficiency1 in 50,000
Propionyl-CoA carboxylasePropionyl-CoAPCCA, PCCBPropionic acidemia1 in 100,000
Methylmalonyl-CoA carboxylaseMethylmalonyl-CoAMUTMethylmalonic acidemia1 in 80,000
Pyruvate carboxylasePyruvatePCPyruvate carboxylase deficiency1 in 250,000
Acetyl-CoA carboxylaseAcetyl-CoAACACA, ACACBNot typically associated with inherited diseaseN/A

These enzymes illustrate the diversity of biotin-dependent metabolism. While all require biotin, their substrates, genetic causes, and clinical impacts vary significantly, with MCC deficiency being among the more commonly detected in newborn screening.

Why It Matters

Understanding MCC function and deficiency has significant implications for diagnosis, treatment, and genetic counseling in metabolic medicine. Early detection can prevent life-threatening metabolic crises.

Continued research into MCC and related enzymes enhances our ability to diagnose and manage inborn errors of metabolism, improving outcomes for affected individuals worldwide.

Sources

  1. WikipediaCC-BY-SA-4.0

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