a potent protein phosphatase 1A and 2A inhibitor.

Polyether derivative of C-38 fatty acid‚ C₄₄H₆₈O₁₃ ‚ from the microorganism Prorocentrum lima.

Very potent inhibitor of protein phosphatases-1 (PP1) and -2A (PP2A) that also stimulates the phosphorylation of many proteins [2]. 1 nM completely inhibits PP2A‚ IC50 ~0.1 nM. IC50 = 10-15 nM for PP1. IC50 = 5 µM for PP2B; 10 µM have no effect on PP2C [4].

Causes a durable contraction of isolated vascular smooth muscles from human umbilical arteries (0.1-100 µM) and rabbit aorta (10 µM)‚ indicating that myosin P-light chain phosphorylation is increased [1-2].

Causes Diarrhetic Shellfish Poisoning (DSP)‚ probably by stimulating the phosphorylation of proteins that control sodium secretion by intestinal cells [2].
Powerful tumour promoter. In two-stage carcinogenesis experiments on mouse skin‚ is of comparable potency to agents like phorbol esters‚ which exert their effects by activating protein kinase C [2].

It reproduces the effects of Insulin on glucose transport in adipocytes [1].

Diffuses through the cell membrane.

1. Haysted et al., "Effects of the tumour promoter okadaic acid on intracellular protein phosphorylation and metabolism." Nature (1989). 337:78-81
2. Cohen et al., "Okadaic acid: a new probe for the study of cellular regulation." TIBS (1990). 15:98-102
3. Shibata et al., "Contractile Effects of Okadaic Acid, a novel Ionophore-Like Substance from Black Sponge, on Isolated Smooth Muscles Under the Condition of Ca Deficiency." J. Pharmacol. Exp. Therap. (1982). 233(1):135-143
4. Cohen et al., FEBS Letters (1989). 250:596-600