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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Ser/Thr-specific protein phosphatases are required for both catalytic steps of pre-mRNA splicing
TL;DR: Protein phosphatase activity was not required for efficient assembly of splicing complexes containing each of the U1, U2, U4/U6 and U5 snRNPs, indicating that reversible protein phosphorylation may play an important role in regulating the pre-mRNA splicing mechanism.
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Characterization of natural toxins with inhibitory activity against serine/threonine protein phosphatases
TL;DR: This study shows that, like PP1 and PP2A, the activity of PP3 is potently inhibited by okadaic acid, both microcystins, nodularin, calyculin A and tautomycin, and shows that the chemical modification of the (C1) carboxyl group of okADAic acid can have a profound influence on the inhibitory activity of this toxin.
Journal ArticleDOI
Fostriecin, an antitumor antibiotic with inhibitory activity against serine/threonine protein phosphatases types 1 (PP1) and 2A (PP2A), is highly selective for PP2A.
TL;DR: Dose‐inhibition studies conducted with whole cell homogenates indicate that fostriecin also inhibits the native forms of PP1 and PP2A, and studies with recombinant PP1/PP2A chimeras indicate that okadaic acid and fostriECin have different binding sites.
Journal ArticleDOI
Reversible light/dark modulation of spinach leaf nitrate reductase activity involves protein phosphorylation
Joan L. Huber,Steven C. Huber,Steven C. Huber,Wilbur H. Campbell,Margaret G. Redinbaugh,Margaret G. Redinbaugh +5 more
TL;DR: In this article, the authors found that the sensitivity of NR to inhibition by millimolar concentrations of magnesium was increased when the leaves were returned to darkness, and the NR rapidly became sensitive to Mg2+ inhibition.
Reversible light/dark modulation of spinach leaf nitrate reductase activity involves protein phosphorylation[F600]; spinacia oleracea; nitrate reductase; enzyme activity; nitrate reduction; phosphorylation; tyrosine; serine; threonine; binding site; molybdenum; electron transfer; inhibition; magnesium; leaves; light; dark; enzyme inhibitors; phosphoric monoester hydrolases IND92070354
TL;DR: NR activity may be controlled in leaves by phosphorylation/dephosphorylation of the enzyme protein resulting from metabolic changes taking place during light/dark transitions, and the current results are highly suggestive of one.
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