Okadaic acid ammonium salt, a marine toxin, serves as an inhibitor of protein phosphatases (PP), displaying a higher affinity for PP2A (IC 50 =0.1-0.3 nM) alongside inhibitory effects on PP1 (IC 50 =15-50 nM), PP3 (IC 50 =3.7-4 nM), PP4 (IC 50 =0.1 nM), and PP5 (IC 50 =3.5 nM), but does not affect PP2C. By inhibiting PPs, this compound promotes protein phosphorylation and acts as a tumor promoter. Additionally, it is involved in inducing tau phosphorylation.