enzymology An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

, a 2-isopropylmalate synthase () is an

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

that

catalyzes Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

the

chemical reaction A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...

:acetyl-CoA + 3-methyl-2-oxobutanoate + H₂O

\rightleftharpoons

(2S)-2-isopropylmalate + CoA The three substrates of this enzyme are

acetyl-CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidation, o ...

, 3-methyl-2-oxobutanoate, and H₂O, and its

products Product may refer to: Business * Product (business), an item that can be offered to a market to satisfy the desire or need of a customer. * Product (project management), a deliverable or set of deliverables that contribute to a business solution ...

are (2S)-2-isopropylmalate and CoA. The enzyme belongs to the family of

transferase In biochemistry, a transferase is any one of a class of enzymes that catalyse the transfer of specific functional groups (e.g. a methyl or glycosyl group) from one molecule (called the donor) to another (called the acceptor). They are involved ...

s, specifically those

acyltransferases Acyltransferase is a type of transferase enzyme that acts upon acyl groups. Examples include: * Glycerol-3-phosphate acyltransferases * Glyceronephosphate O-acyltransferase * Lecithin-cholesterol acyltransferase *Long-chain-alcohol O-fatty-acyl ...

that convert acyl groups into alkyl groups on transfer. The

systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature. A semisystematic name or semitrivi ...

of this enzyme class is ''acetyl-CoA:3-methyl-2-oxobutanoate C-acetyltransferase (thioester-hydrolysing, carboxymethyl-forming)''. Other names in common use include ''3-carboxy-3-hydroxy-4-methylpentanoate 3-methyl-2-oxobutanoate-lyase'', ''(CoA-acetylating)'', ''alpha-isopropylmalate synthetase'', ''alpha-isopropylmalate synthase'', ''alpha-isopropylmalic synthetase'', ''isopropylmalate synthase'', and ''isopropylmalate synthetase''. This enzyme participates in biosynthesis of L-

leucine Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins. Leucine is an α-amino acid, meaning it contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α-Car ...

and

pyruvate metabolism Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell. Pyruvic ac ...

. Monovalent and divalent cation activation have been reported for enzymes from different sources. ''

Mycobacterium tuberculosis ''Mycobacterium tuberculosis'' (M. tb), also known as Koch's bacillus, is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis. First discovered in 1882 by Robert Koch, ''M. tuberculosis'' ha ...

'' α-isopropylmalate synthase requires a divalent metal ion, of which Mg²⁺ and Mn²⁺ give highest activity, and a monovalent cation, with K⁺ as the best activator. Zn²⁺ was shown to be an inhibitor, contrary to what was assumed from the structural data. Another feature of the ''M. tuberculosis'' homolog is that L-leucine, the feedback inhibitor, inhibits the enzyme in a time-dependent fashion. This was the first demonstration of a feedback inhibitor that displays slow-onset inhibition.

Tertiary structure

As of late 2007, only one

tertiary structure Protein tertiary structure is the three-dimensional shape of a protein. The tertiary structure will have a single polypeptide chain "backbone" with one or more protein secondary structures, the protein domains. Amino acid side chains and the ...

has been solved for this class of enzymes, with the

Protein Data Bank The Protein Data Bank (PDB) is a database for the three-dimensional structural data of large biological molecules such as proteins and nucleic acids, which is overseen by the Worldwide Protein Data Bank (wwPDB). This structural data is obtained a ...

accession code .

References

EC 2.3.3 Potassium enzymes Enzymes of known structure {{2.3-enzyme-stub