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Biological Research

Print version ISSN 0716-9760

Abstract

RIVAS, MARIELLA; GARCIA, CARLOS; LIBERONA, JOSÉ L  and  LAGOS, NÉSTOR. Biochemical characterization and inhibitory effects of dinophysistoxin-1, okadaic acid and microcystine l-r on protein phosphatase 2a purified from the mussel Mytilus chilensis. Biol. Res. [online]. 2000, vol.33, n.3-4, pp.197-206. ISSN 0716-9760.  http://dx.doi.org/10.4067/S0716-97602000000300005.

Protein phosphatases are involved in many cellular processes. One of the most abundant and best studied members of this class is protein phosphatase type-2A (PP2A). In this study, PP2A was purified from the mussel Mytilus chilensis. Using both SDS-PAGE and size exclusion gel filtration under denaturant conditions, it was confirmed that the PP2A fraction was essentially pure. The isolated enzyme is a heterodimer and the molecular estimated masses of the subunits are 62 and 28 kDa. The isolated PP2A fraction has a notably high p-NPP phosphatase activity, which is inhibited by NaCl. The hydrolytic p-NPP phosphatase activity is independent of the MgCl2 concentration. The time courses of the inhibition of the PP2A activity of p-NPP hydrolysis by increasing concentrations of three phycotoxins that are specific inhibitors of PP2A are shown. Inhibitions caused by Okadaic acid, dinophysistoxin-1 (DTX1, 35-methylokadiac acid) and Microcystine L-R are dose-dependent with inhibition constants (Ki) of 1.68, 0.40 and 0.27 nM respectively. Microcystine L-R, the most potent phycotoxin inhibitor of PP2A isolated from Mytilus chilensis with an IC50 = 0.25 ng/ml, showed the highest specific inhibition effect an the p-NPP hydrolisis. The calculated IC50 for DTX1 and OA was 0.75 ng/ml and 1.8 ng/ml respectively.

Keywords : Chile; Diarrhetic Shellfish Poisoning (DSP); Mussel; Mytilus chilensis; Protein Phosphatase 2A; Microcystine L-R.

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