What Is 2-methylacyl-CoA dehydrogenase

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Last updated: April 15, 2026

Quick Answer: 2-Methylacyl-CoA dehydrogenase (2-MACD) is a mitochondrial enzyme involved in the beta-oxidation of branched-chain fatty acids, particularly those derived from the metabolism of isoleucine. Deficiency in this enzyme leads to a rare inherited metabolic disorder with symptoms appearing in infancy. It was first characterized in the early 1990s through biochemical and genetic studies.

Key Facts

2-Methylacyl-CoA dehydrogenase is encoded by the ACADSB gene located on chromosome 10q25-q26
The enzyme plays a critical role in the beta-oxidation of 2-methyl-branched fatty acyl-CoAs
Deficiency was first reported in 1992 in a patient with metabolic acidosis and developmental delay
Over 20 pathogenic variants in ACADSB have been linked to 2-MACD deficiency
Newborn screening does not routinely detect 2-MACD deficiency due to low incidence

Overview

2-Methylacyl-CoA dehydrogenase (2-MACD) is an enzyme essential for the metabolism of certain branched-chain fatty acids, particularly those derived from the amino acid isoleucine. It functions within the mitochondria, where it catalyzes a step in the beta-oxidation pathway that breaks down 2-methyl-substituted fatty acyl-CoA esters.

This enzyme is part of the acyl-CoA dehydrogenase family, which includes several enzymes specialized for different chain lengths and structures of fatty acids. Its specificity for 2-methyl-branched substrates distinguishes it from other dehydrogenases like SCAD or LCAD.

Gene location: The ACADSB gene encoding 2-MACD is located on chromosome 10q25-q26, spanning approximately 7.5 kilobases with 10 exons.
Substrate specificity: 2-MACD primarily acts on 2-methylbutyryl-CoA, a metabolite derived from the catabolism of isoleucine.
Enzyme class: It belongs to the acyl-CoA dehydrogenase family, which uses FAD as a cofactor to initiate dehydrogenation.
Metabolic pathway: It participates in the mitochondrial beta-oxidation pathway, converting substrates into enoyl-CoAs for further processing.
Disease link: Mutations in ACADSB cause 2-methylacyl-CoA dehydrogenase deficiency, a rare autosomal recessive disorder affecting fatty acid oxidation.

How It Works

2-Methylacyl-CoA dehydrogenase catalyzes the first step in the beta-oxidation of 2-methyl-branched fatty acyl-CoAs, introducing a double bond between the alpha and beta carbons. This reaction is essential for the continued breakdown of specific branched-chain lipids and amino acid derivatives.

Reaction: 2-MACD catalyzes the dehydrogenation of 2-methylbutyryl-CoA to form tiglyl-CoA, using FAD as an electron acceptor.
Enzyme structure: The functional enzyme is a homotetramer with each subunit weighing approximately 43 kDa.
Cofactor: It requires FAD (flavin adenine dinucleotide) to transfer electrons to the electron transfer flavoprotein (ETF).
Subcellular location: 2-MACD is localized in the mitochondrial matrix, where beta-oxidation occurs.
Gene expression: ACADSB is highly expressed in liver and skeletal muscle, tissues with high fatty acid oxidation rates.
Regulation: Expression is regulated by PPAR-alpha, a nuclear receptor that activates fatty acid metabolism genes during fasting.

Comparison at a Glance

2-MACD shares structural and functional similarities with other acyl-CoA dehydrogenases but differs in substrate specificity and genetic basis.

Enzyme	Gene	Substrate	Associated Disorder	OMIM Entry
2-Methylacyl-CoA dehydrogenase	ACADSB	2-methylbutyryl-CoA	2-MACD deficiency	600861
Short-chain acyl-CoA dehydrogenase	ACADS	Butyryl-CoA	SCAD deficiency	606885
Medium-chain acyl-CoA dehydrogenase	ACADM	Octanoyl-CoA	MCAD deficiency	201450
Isobutyryl-CoA dehydrogenase	ACAD8	Isobutyryl-CoA	IBD deficiency	609584
Glutaryl-CoA dehydrogenase	GCDH	Glutaryl-CoA	Glutaric acidemia type I	231670

This comparison highlights how each enzyme in the acyl-CoA dehydrogenase family targets specific substrates and is linked to distinct metabolic disorders when deficient. While 2-MACD is less commonly tested in newborn screening panels, its role in isoleucine catabolism makes it critical for energy production during prolonged fasting or catabolic stress.

Why It Matters

Understanding 2-methylacyl-CoA dehydrogenase is vital for diagnosing and managing rare metabolic disorders, particularly in pediatric patients with unexplained metabolic crises.

Diagnostic significance: Deficiency can mimic other organic acidemias, requiring urine organic acid analysis and acylcarnitine profiling for detection.
Clinical presentation: Affected individuals may present with hypoglycemia, metabolic acidosis, and lethargy during infancy.
Genetic testing: Sequencing of ACADSB confirms diagnosis and enables carrier testing in families.
Treatment: Management includes avoiding fasting and providing high-carbohydrate, low-fat diets to reduce metabolic stress.
Prognosis: Early diagnosis and dietary intervention can lead to normal neurodevelopment in many cases.
Research impact: Studying 2-MACD contributes to broader understanding of mitochondrial metabolism and fatty acid disorders.

As genomic screening expands, more cases of 2-MACD deficiency may be identified incidentally, emphasizing the need for accurate interpretation of metabolic data and enzyme function.