What Is 3-oxoadipate CoA-transferase

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Last updated: April 15, 2026

Quick Answer: 3-oxoadipate CoA-transferase is an enzyme (EC 2.8.3.6) involved in the degradation of aromatic compounds in bacteria, catalyzing the transfer of CoA from succinyl-CoA to 3-oxoadipate to form 3-oxoadipyl-CoA. It plays a key role in the β-ketoadipate pathway, which is essential for the catabolism of lignin-derived aromatics in soil microbes like Pseudomonas.

Key Facts

3-oxoadipate CoA-transferase has EC number 2.8.3.6, classified under transferases.
It catalyzes the reaction: 3-oxoadipate + succinyl-CoA → 3-oxoadipyl-CoA + succinate.
The enzyme is part of the β-ketoadipate pathway in bacteria such as Pseudomonas putida.
It enables microbial degradation of aromatic compounds like protocatechuate and catechol.
Structural studies show it uses a ping-pong mechanism with a conserved glutamate residue.

Overview

3-oxoadipate CoA-transferase is a bacterial enzyme critical in the breakdown of aromatic compounds, particularly in soil-dwelling microbes like Pseudomonas putida. It functions within the β-ketoadipate pathway, a central metabolic route that converts plant-derived aromatics into intermediates usable in the Krebs cycle.

This enzyme specifically mediates the transfer of coenzyme A (CoA) from succinyl-CoA to 3-oxoadipate, forming 3-oxoadipyl-CoA and succinate. Its activity is essential for bacteria to utilize aromatic molecules as carbon sources, especially in environments rich in lignin and polyphenolic compounds.

Enzyme classification: It is designated EC 2.8.3.6, placing it in the CoA-transferase subclass of transferases that move CoA moieties between organic acids.
Substrate specificity: The enzyme shows high affinity for 3-oxoadipate and succinyl-CoA, with a Km of approximately 15 μM for 3-oxoadipate in P. putida.
Genetic basis: The gene encoding this enzyme, often named pcaI or pcaJ, is part of the pca gene cluster regulated by aromatic compounds.
Cellular location: Found in the cytoplasm of Gram-negative bacteria, where it operates under neutral pH conditions optimal for its activity.
Evolutionary role: It evolved to support microbial recycling of plant biomass, playing a crucial role in carbon cycling in forest and agricultural soils.

How It Works

The mechanism of 3-oxoadipate CoA-transferase involves a two-step ping-pong reaction, where the enzyme first binds succinyl-CoA, releases succinate, and forms an enzyme-CoA intermediate before transferring CoA to 3-oxoadipate.

Step 1 - CoA donation:Succinyl-CoA binds to the enzyme, leading to the release of succinate and the formation of a covalent acyl-enzyme intermediate with CoA.
Step 2 - CoA transfer:3-oxoadipate enters the active site, where the enzyme-bound CoA is transferred, forming 3-oxoadipyl-CoA, the substrate for the next enzyme in the pathway.
Catalytic residue: A conserved glutamate residue (Glu328 in P. putida) acts as a catalytic base, essential for CoA transfer and confirmed via site-directed mutagenesis.
Kinetic efficiency: The enzyme has a kcat of 48 s⁻¹ and a catalytic efficiency (kcat/Km) of 3.2 × 10⁶ M⁻¹s⁻¹ for 3-oxoadipate under physiological conditions.
pH optimum: Maximum activity occurs at pH 7.5–8.0, consistent with its cytoplasmic localization and role in neutral metabolic environments.
Structural insight: X-ray crystallography reveals a homodimeric structure with each subunit containing a CoA-binding pocket and a flexible loop that gates substrate access.

Comparison at a Glance

The following table compares 3-oxoadipate CoA-transferase with related CoA-transferases based on substrate specificity, kinetics, and biological role:

Enzyme	EC Number	Primary Substrate	Organism	kcat (s⁻¹)
3-oxoadipate CoA-transferase	2.8.3.6	3-oxoadipate	Pseudomonas putida	48
Succinyl-CoA:3-ketoacid CoA-transferase	2.8.3.5	Acetoacetate	Mammals	22
Butyryl-CoA transferase	2.8.3.12	Butyrate	Clostridium spp.	15
Acetyl-CoA:acetate CoA-transferase	2.8.3.8	Acetate	E. coli	35
Phenylacetate CoA-transferase	2.8.3.15	Phenylacetate	E. coli	28

While all these enzymes transfer CoA, 3-oxoadipate CoA-transferase stands out due to its role in aromatic catabolism. Unlike generalist CoA-transferases, it evolved to handle structurally complex ring-cleavage products, making it indispensable in biodegradation pathways. Its higher turnover rate compared to some homologs reflects adaptation to high-flux metabolic conditions in soil bacteria.

Why It Matters

Understanding 3-oxoadipate CoA-transferase has broad implications for environmental microbiology, bioremediation, and bioengineering. Its function enables microbes to break down toxic aromatic pollutants, supporting ecosystem resilience and carbon cycling.

Bioremediation: Bacteria expressing this enzyme can degrade lignin derivatives and pollutants like benzoate and phthalate, reducing soil and water contamination.
Bioengineering: The pcaIJ genes are used in synthetic biology to engineer strains that convert plant biomass into biofuels and bioplastics.
Carbon cycling: It contributes to the global carbon cycle by mineralizing aromatic compounds into CO₂ and cellular metabolites in forest ecosystems.
Enzyme evolution: Studies of its structure inform how substrate specificity evolves in CoA-transferase families, guiding protein engineering.
Medical relevance: Homologous pathways in pathogens suggest potential targets for antibiotic development against aromatic amino acid metabolism.
Industrial applications: Engineered variants are tested in biocatalysis for the green synthesis of chiral CoA-thioesters used in pharmaceuticals.

As research advances, 3-oxoadipate CoA-transferase continues to emerge as a model enzyme for studying metabolic adaptation and microbial ecology, bridging fundamental biochemistry with real-world sustainability challenges.