1-Aminocyclopropanecarboxylic acid is a small molecule agonist at the glycine modulatory site of the NMDA receptor. Described to mimic the effects of glycine at the NMDAR, 1-Aminocyclopropanecarboxylic acid competitively inhibits binding of [3H]glycine and enhances the binding of [3H]MK-801 to NMDAR-coupled cation channels similarly to glycine (though with less efficacy).