The enzyme methylaspartate ammonia-lyase (EC 4.3.1.2) catalyzes the chemical reaction This enzyme belongs to the family of lyases, specifically ammonia lyases, which cleave carbon-nitrogen bonds.

The systematic name of this enzyme class is L-threo-3-methylaspartate ammonia-lyase (mesaconate-forming).

Other names in common use include β-methylaspartase, 3-methylaspartase, and L-threo-3-methylaspartate ammonia-lyase.

It employs one cofactor, cobamide.

Several structures of this enzyme have been deposited in the Protein Data Bank (linked in the infobox) which show it possesses a TIM barrel domain.