Inhibitory effect of a marine-sponge toxin, okadaic acid, on protein phosphatases. Specificity and kinetics
Corinna Bialojan,Akira Takai +1 more
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Kinetic studies showed that okadaic acid acts as a non-competitive or mixed inhibitor on the okadaIC acid-sensitive enzymes.Abstract:
The inhibitory effect of a marine-sponge toxin, okadaic acid, was examined on type 1, type 2A, type 2B and type 2C protein phosphatases as well as on a polycation-modulated (PCM) phosphatase. Of the protein phosphatases examined, the catalytic subunit of type 2A phosphatase from rabbit skeletal muscle was most potently inhibited. For the phosphorylated myosin light-chain (PMLC) phosphatase activity of the enzyme, the concentration of okadaic acid required to obtain 50% inhibition (ID50) was about 1 nM. The PMLC phosphatase activities of type 1 and PCM phosphatase were also strongly inhibited (ID50 0.1-0.5 microM). The PMCL phosphatase activity of type 2B phosphatase (calcineurin) was inhibited to a lesser extent (ID50 4-5 microM). Similar results were obtained for the phosphorylase a phosphatase activity of type 1 and PCM phosphatases and for the p-nitrophenyl phosphate phosphatase activity of calcineurin. The following phosphatases were not affected by up to 10 microM-okadaic acid: type 2C phosphatase, phosphotyrosyl phosphatase, inositol 1,4,5-trisphosphate phosphatase, acid phosphatases and alkaline phosphatases. Thus okadaic acid had a relatively high specificity for type 2A, type 1 and PCM phosphatases. Kinetic studies showed that okadaic acid acts as a non-competitive or mixed inhibitor on the okadaic acid-sensitive enzymes.read more
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MPF Amplification inXenopusOocyte Extracts Depends on a Two-Step Activation of Cdc25 Phosphatase
TL;DR: A cell-free system prepared from prophase-arrested Xenopus oocytes is developed to analyze the mechanism initiating the all-or-none activation of Cdc2 kinase, and it is demonstrated that, under the authors' conditions, CDC2 amplification and MAP kinase activation are two independent events.
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Cdk1 and okadaic acid-sensitive phosphatases control assembly of nuclear pore complexes in Drosophila embryos.
TL;DR: A novel in vivo model system based on syncytial Drosophila embryos is developed and suggests a model where mitotic disassembly/reassembly of the NPCs is regulated by a dynamic equilibrium of Cdk1 and OA-sensitive phosphatase activities and provides evidence that mitotic phosphorylation mediates dis assembly of the NPC.
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Enzyme sensor for the electrochemical detection of the marine toxin okadaic acid.
Mònica Campàs,Jean-Louis Marty +1 more
TL;DR: In this article, an enzyme sensor for the electrochemical detection of the marine toxin okadaic acid (OA) has been developed, based on the inhibition of immobilised protein phosphatase (PP2A) by this toxin and the measurement of the enzyme activity by the use of appropriate enzyme substrates, electrochemically active after dephosphorylation by the enzyme.
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Regulation of the contractile element of airway smooth muscle.
TL;DR: It is suggested that the contractile element sensitivity to Ca2+ is not fixed but might be modulated by undefined messengers or excitation-contraction pathways, which adds an additional challenge to the continuing effort to define the messengers and regulatory proteins that couple activation of membrane receptors in airway smooth muscle.
Journal ArticleDOI
Depuration of Okadaic acid (Diarrhetic Shellfish Toxin) in mussels, Mytilus edulis (Linnaeus), feeding on different quantities of nontoxic algae
TL;DR: It was concluded that the rate of depuration of OA in mussels is not positively correlated with digestive activity and fecal production, and the lipophilic character of the OA molecule suggests that OA may have affinity for lipid-rich cellular and intracellular components.
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