Inhibitory effect of a marine-sponge toxin, okadaic acid, on protein phosphatases. Specificity and kinetics
Corinna Bialojan,Akira Takai +1 more
Reads0
Chats0
TLDR
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
Citations
More filters
Journal ArticleDOI
Differential involvement of reactive oxygen species in apoptosis caused by the inhibition of protein phosphatase 2A in Jurkat and CCRF-CEM human T-leukemia cells.
TL;DR: Jurkat and CCRF-CEM human T-leukemia cell lines were more sensitive than normal human T cells to the cytotoxic effect of inhibiting protein phosphatase 2A (PP2A), and PP2A might be a useful intracellular target for the treatment of T cell-derived leukemias.
Journal ArticleDOI
Multidrug-resistant human KB carcinoma cells are highly resistant to the protein phosphatase inhibitors okadaic acid and calyculin A. Analysis of potential mechanisms involved in toxin resistance.
TL;DR: A novel, marked resistance of MDR KB‐VI cells to these phosphatase inhibitors is demonstrated and it is suggested that a major mechanism of resistance may involve toxin transport by P‐gp at sites apparently different from those which bind azidopine.
Journal ArticleDOI
Okadaic acid stimulates osteopontin expression through de novo induction of AP-1.
TL;DR: Site‐directed mutagenesis and electrophoretic mobility shift assays confirmed that protein binding of the AP‐1 consensus sequence is necessary for the okadaic acid‐mediated osteopontin gene upregulation.
Book ChapterDOI
Toxicity of Sea Algal Toxins to Humans and Animals
TL;DR: Algal toxins are responsible for extensive die-offs of fish and shellfish, as well as mortality in seabirds, marine mammals and other animals depending on marine food web, and little is known about environmental health effects of chronic exposure to low levels of algal toxins.
Journal ArticleDOI
Inhibition of serine/threonine protein phosphatases by secretagogues in insulin-secreting cells
TL;DR: It is concluded that insulin secretagogues cause time- and concentration-dependent inhibitory effects on RINm5F cell PPase activities, which may contribute to the increase in the phosphorylation state that occurs after stimulation of insulin release.
References
More filters
Journal Article
Protein Measurement with the Folin Phenol Reagent
TL;DR: Procedures are described for measuring protein in solution or after precipitation with acids or other agents, and for the determination of as little as 0.2 gamma of protein.
Journal ArticleDOI
The direct linear plot. A new graphical procedure for estimating enzyme kinetic parameters
TL;DR: A new plot is described for analysing the results of kinetic experiments in which the Michaelis-Menten equation is obeyed, and provides clear and accurate information about the quality of the observations, and identifies aberrant observations.
Journal ArticleDOI
The kinetics of enzyme-catalyzed reactions with two or more substrates or products. II. Inhibition: nomenclature and theory.
TL;DR: A nomenclature is proposed to describe different types of inhibitions of enzyme-catalyzed reactions, particularly for reactions with more than one substrate and product, and the rate equations for such inhibitions are discussed.
Journal ArticleDOI
Discovery of A Ca2+-and calmodulin-dependent protein phosphatase
TL;DR: The serine residue on the a-sub unit, as well as that on the@subunit, becomes phosphorylated in vivo in response to adrenaline, suggesting that it may have a physiological function.
Journal ArticleDOI
The protein phosphatases involved in cellular regulation. 1. Classification and substrate specificities.
TL;DR: Examination of the amino acid sequences around each phosphorylation site does not support the idea that protein phosphatase specificity is determined by the primary structure in the immediate vicinity of the phosphorylated site, and demonstrates that proteinosphatase-1 and protein phosph atase 2A have very broad substrate specificities.