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In enzymology, a maleate isomerase , or maleate cis-tran isomerase, is a member of the Asp/Glu racemase superfamily discovered in bacteria. It is responsible for catalyzing cis-trans isomerization of the C2-C3 double bond in maleate to produce fumarate, which is a critical intermediate in citric acid cycle. The presence of an exogenous mercaptan is required for catalysis to happen.
Maleate isomerase participates in butanoate metabolism and nicotinate and nicotinamide metabolism. It is an essential enzyme for the last step of metabolic degradation pathway of nicotinic acid. Recently, maleate isomerase has been an industrial target for degradation of tobacco waste. It is also got attention for its involvement in aspartic acid and maleic acid production.
Maleate isomerase has been utilized by multiple bacteria species, including Pseudomonas fluorescens, Alcaligenes faecalis, Bacillus stearothermophilus, Serratia marcescens, Pseudomonas putida and Nocardia farcinica. The enzyme has a molecular weight of 74,000 and a turnover number of 1,800 moles per mole of protein per min.