coenzyme A

(noun)

A coenzyme, formed from pantothenic acid and adenosine triphosphate, that is necessary for fatty acid synthesis and metabolism.

Related Terms

Examples of coenzyme A in the following topics:

  • Cofactors and Energy Transitions

    • For example, the multienzyme complex pyruvate dehydrogenase at the junction of glycolysis and the citric acid cycle requires five organic cofactors and one metal ion: loosely bound thiamine pyrophosphate (TPP), covalently bound lipoamide and flavin adenine dinucleotide (FAD), and the cosubstrates nicotinamide adenine dinucleotide (NAD+) and coenzyme A (CoA), and a metal ion (Mg2+).
    • Many contain the nucleotide adenosine monophosphate (AMP) as part of their structures, such as ATP, coenzyme A, FAD, and NAD+.
    • It has been suggested that the AMP part of the molecule can be considered a kind of "handle" by which the enzyme can "grasp" the coenzyme to switch it between different catalytic centers.
    • Many organic cofactors also contain a nucleotide, such as the electron carriers NAD and FAD, and coenzyme A, which carries acyl groups.
    • These group-transfer intermediates are the loosely-bound organic cofactors, often called coenzymes.

  • Citric Acid and Other Organic Compounds

    • It is produced from acetyl coenzyme A and oxaloacetate in the presence of the enzyme citrate synthase.
    • It is used as a food additive to give a sour taste to foods or to preserve certain qualities of food products (e.g., prevents separating of the fats in ice cream).
    • It has natural antibacterial properties and is used as a preservative as well.
    • The mold is grown in a medium with sucrose or glucose as the main carbon source.

  • Pyruvic Acid and Metabolism

    • Pyruvic acid (CH3COCOOH) is an organic acid, a ketone, and the simplest of the alpha-keto acids.
    • Pyruvic acid (CH3COCOOH; is an organic acid, a ketone, and the simplest of the alpha-keto acids.
    • Pyruvate is converted into acetyl-coenzyme A, which is the main input for a series of reactions known as the Krebs cycle.
    • Pyruvate from glycolysis is converted by fermentation to lactate using the enzyme lactate dehydrogenase and the coenzyme NADH in lactate fermentation.
    • Pyruvate is a key intersection in the network of metabolic pathways.

  • The Reverse TCA Cycle

    • The following is a brief overview of the reverse TCA cycle.
    • Reverse TCA, a form of carbon fixation, utilizes numerous ATP molecules, hydrogen and carbon dioxide to generate an acetyl CoA.
    • 4) succinate is converted to succinyl-CoA (ATP is hydrolyzed to ADP+Pi)
    • 5) succincyl CoA is converted to alpha-ketoglutarate via an alpha-ketoglutarate synthase (reduction of carbon dioxide occurs and oxidation of coenzyme A)
    • An example of a microorganism that utilizes reverse TCA includes Thermoproteus.

  • The Incorporation of Nonstandard Amino Acids

    • A protein (also called a polypeptide) is a chain of amino acids.
    • These modifications are often essential for the function or regulation of a protein.
    • For instance, the addition of long hydrophobic groups can cause a protein to bind to a phospholipid membrane.
    • In alanine, the side-chain is a methyl group; in beta alanine, the side-chain contains a methylene group connected to an amino group, and the alpha carbon lacks an amino group.
    • A rare exception to the dominance of α-amino acids in biology is the β-amino acid beta alanine (3-aminopropanoic acid), which is used in plants and microorganisms in the synthesis of pantothenic acid (vitamin B5), a component of coenzyme A.

  • Types of Catabolism

    • Next, these smaller molecules are taken up by cells and converted to yet smaller molecules, usually the acetyl coenzyme A (acetyl-CoA), which releases some energy.
    • Finally, the acetyl group on the CoA is oxidized to water and carbon dioxide in the citric acid cycle and electron transport chain, releasing the energy that is stored by reducing the coenzyme nicotinamide adenine dinucleotide (NAD+) into NADH.
    • This oxidation releases carbon dioxide as a waste product.
    • An alternative route for glucose breakdown is the pentose phosphate pathway, which reduces the coenzyme NADPH and produces pentose sugars such as ribose, the sugar component of nucleic acids.
    • The amino group is fed into the urea cycle, leaving a deaminated carbon skeleton in the form of a keto acid.

  • Energy Conservation and Autotrophy in Archaea

    • Archaea can use a number of different mechanisms to get nutrients and energy.
    • For example, archaea use a modified form of glycolysis (the Entner–Doudoroff pathway) and either a complete or partial citric acid cycle.
    • Methanogenesis uses a range of coenzymes that are unique to these archaea, such as coenzyme M and methanofuran.
    • Other archaea, called autotrophs, use CO2 in the atmosphere as a source of carbon, in a process called carbon fixation.
    • This process is a form of photophosphorylation.

  • Habitats and Energy Metabolism of Crenarchaeota

    • Crenarchaeota exist in a wide range of habitats and exhibit a great variety of chemical reactions in their metabolism.
    • The Crenarchaeota are Archaea that have been classified as either a phylum of the Archaea kingdom, or in a kingdom of its own.
    • Archaea exist in a broad range of habitats, and as a major part of global ecosystems, they may contribute up to 20% of earth's biomass.
    • Methanogenesis involves a range of coenzymes that are unique to these archaea, such as coenzyme M and methanofuran.
    • Other archaea use CO2 in the atmosphere as a source of carbon, in a process called carbon fixation (they are autotrophs).

  • Methanogenesis

    • Methanogenesis is a form of anaerobic respiration that uses carbon as a electron acceptor and results in the production of methane.
    • The presence of atmospheric methane has a role in the scientific search for extra-terrestrial life!
    • It involves the coenzymes and cofactors F420, coenzyme B, coenzyme M, methanofuran, and methanopterin.
    • Biogenic methane can be collected and used as a sustainable alternative to fossil fuels.
    • Acetate is broken down to methane by methanogenesis, a type of anaerobic respiration.

  • Carboxysomes

    • Similar structures are known to harbor the B12-containing coenzyme glycerol dehydratase, the key enzyme of glycerol fermentation to 1,3-propanediol, in some Enterobacteriaceae, such as Salmonella.
    • Carboxysomes are an example of a wider group of protein micro-compartments that have dissimilar functions but similar structures, based on homology of the two shell protein families.
    • Carboxysomes were first purified from Thiobacillus neapolitanus in 1973, and were shown to contain RuBisCo held within a rigid outer covering .
    • (A) A thin-section electron micrograph of H. neapolitanus cells with carboxysomes inside.
    • (B) A negatively stained image of intact carboxysomes isolated from H. neapolitanus.