Isatin (Indoline-2,3-dione) is a potent inhibitor of monoamine oxidase (MAO) with an IC50 of 3 μM. Also binds to central benzodiazepine receptors (IC50 against clonazepam, 123 μM) [1]. Also acts as an antagonist of both atrial natriuretic peptide stimulated and nitric oxide-stimulated guanylate cyclase activity[2]. Shows effect on the serotonergic system[3].