fatty acid

fatty acid

fatty acid, any of the organic carboxylic acids present in fats and oils as esters of glycerol. Molecular weights of fatty acids vary over a wide range. The carbon skeleton of any fatty acid is unbranched. Some fatty acids are saturated, i.e., each carbon atom is connected to its carbon atom neighbors by single bonds; and some fatty acids are unsaturated, i.e., contain at least one carbon-carbon double bond (see chemical bond). When fats and oils are hydrolyzed with an alkali, the fatty acids are liberated as their metal salts; these salts are soaps. Butyric acid is a fatty acid found in butter.

Organic compound that is an important component of lipids in plants, animals, and microorganisms. Fatty acids are carboxylic acids with a long hydrocarbon chain, usually straight, as the fourth substituent group on the carboxyl (singlehorzbondCOOH) group (see functional group) that makes the molecule an acid. If the carbon-to-carbon bonds (see bonding) in that chain are all single, the fatty acid is saturated; artificial saturation is called hydrogenation. A fatty acid with one double bond is monounsaturated; one with more is polyunsaturated. These are more reactive chemically. Most unsaturated fats are liquid at room temperature, so food manufacturers hydrogenate them to make them solid (see margarine). A high level of saturated fatty acids in the diet raises blood cholesterol levels. A few fatty acids have branched chains. Others (e.g., prostaglandins) contain ring structures. Fatty acids in nature are always combined, usually with glycerol as triglycerides in fats. Oleic acid (unsaturated, with 18 carbon atoms) is almost half of human fat and is abundant in such oils as olive, palm, and peanut. Most animals, including mammals, cannot synthesize some unsaturated “essential” fatty acids; humans need linoleic, linolenic, and arachidonic acids in their diet.

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In enzymology, a long-chain-fatty-acid-[acyl-carrier-protein] ligase is an enzyme that catalyzes the chemical reaction

ATP + an acid + [acyl-carrier-protein] rightleftharpoons AMP + diphosphate + acyl-[acyl-carrier-protein]

The 3 substrates of this enzyme are ATP, acid, and [acyl-carrier-protein], whereas its 3 products are AMP, diphosphate, and acyl-[acyl-carrier-protein].

This enzyme belongs to the family of ligases, specifically those forming carbon-sulfur bonds as acid-thiol ligases. The systematic name of this enzyme class is long-chain-fatty-acid:[acyl-carrier-protein] ligase (AMP-forming). Other names in common use include acyl-[acyl-carrier-protein] synthetase, acyl-[acyl carrier protein] synthetase, acyl-ACP synthetase, acyl-[acyl-carrier-protein]synthetase, stearoyl-ACP synthetase, and acyl-acyl carrier protein synthetase. This enzyme participates in fatty acid metabolism.


  • Ray TK, Cronan JE Jr "Activation of long chain fatty acids with acyl carrier protein: demonstration of a new enzyme, acyl-acyl carrier protein synthetase, in Escherichia coli". Proc. Natl. Acad. Sci. U. S. A. 73 4374–8.

External links

The CAS registry number for this enzyme class is .

Gene Ontology (GO) codes

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