Methylaspartate ammonia lyase (3-methylaspartase, MAL) is a homodimeric enzyme, catalyzing the magnesium-dependent reversible alpha,beta-elimination of ammonia from L-threo-(2S,3S)-3-methylaspartic acid to mesaconic acid. This reaction is part of the main catabolic pathway for glutamate. MAL belongs to the enolase superfamily of enzymes, characterized by the presence of an enolate anion intermediate which is generated by abstraction of the alpha-proton of the carboxylate substrate by an active site residue and is stabilized by coordination to the essential Mg2+ ion.
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