4-Oxalocrotonate tautomerase

4-Oxalocrotonate tautomerase (EC 5.3.2.-4-OT) is an enzyme that converts 2-hydroxymuconate to the αβ-unsaturated ketone, 2-oxo-3-hexenedioate. [cite journal |author=Chen LH, Kenyon GL, Curtin F, Harayama S, Bembenek ME, Hajipour G, Whitman CP |title=4-Oxalocrotonate tautomerase, an enzyme composed of 62 amino acid residues per monomer |journal=J. Biol. Chem. |volume=267 |issue=25 |pages=17716–21 |year=1992 |pmid=1339435] This enzyme forms part of a bacterial metabolic pathway that oxidatively catabolizes toluene, p-xylene, 3-ethyltoluene, and 1,2,4-trimethylbenzene into intermediates of the citric acid cycle. With a monomer size of just 62 amino acid residues, the 4-Oxalocrotonate tautomerase is one of the smallest enzyme subunits known. [cite journal |author=Whitman CP |title=The 4-oxalocrotonate tautomerase family of enzymes: how nature makes new enzymes using a beta-alpha-beta structural motif |journal=Arch. Biochem. Biophys. |volume=402 |issue=1 |pages=1–13 |year=2002 |pmid=12051677 |doi=10.1016/S0003-9861(02)00052-8] However, in solution the enzyme forms a hexamer of six identical subunits, so the active site may be formed by amino acid residues from several subunits. This enzyme is also unusual in that it uses a proline residue at the amino terminus as an active site residue.

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