Vertical variations in kinetics of alkaline phosphatase and P species in sediments of a shallow Chinese eutrophic lake (Lake Donghu)

The vertical distribution of the variables relevant to P forms in sediments were studied in a shallow Chinese freshwater lake (Lake Donghu) in 1997, 1998, 1999 and 2000, to assess the contribution of enzyme to P availability in sediment cores. Sediment P was fractionationd into iron-bound P, calcium-bound P, acid soluble organic P (ASOP) and hot NaOH extractable residual organic P. The former two species made the largest contribution to the sediment P pool. All P species exhibited significantly higher concentrations in different depths at Station I, compared with those found at Station II, except for ASOP. Coupled with these lower ASOP concentrations, the V-max data of alkaline phosphatase, measured on the same samples, were significantly higher at station I. Taken together, ASOP were probably important in supplying the enzymatic substrate (Phosphatase Hydrolyzable Phosphorus, PHP) into interstitial water. Dissolved orthophosphate and PHP concentrations were highly heterogeneous , but peaked in subsurface, paralleled by higher V-max and lower K-m values of alkaline phosphatase, throughout the sediment core. Sediment in the eutrophic lake is not only enriched in available P (iron-bound P), or stores residual P, but also tends to release PHP, thereby inducing the production of alkaline phosphatase and releasing o-P into water column by enzymatic hydrolysis. The latter process may also occur in relatively deep sediment layers.

KINETICS OF SIZE-FRACTIONATED AND DISSOLVED ALKALINE-PHOSPHATASE IN A FARM POND

Nutrient addition bioassays were conducted in 10 L carboys with water from a eutrophic farm pond. The four bioassay treatments each conducted in triplicate were control (no nutrients added), +N (160 mu mol L(-1) NH4Cl), +P (10 mu mol L(-1) KH2PO4), and N+P (160 mu mol L(-1) NH4Cl and 10 mu mol L(-1) KH2PO4). The size fractionated (0.2-0.8, 0.8-3, > 3 mu m) contents of the carboys were analyzed after 7 d for alkaline phosphatase activity (APA) and chlorophyll-a content. Chlorophyll data suggested P deficiency in ammonium and control mesocosms and no P deficiency with phosphate additions. Pond water also was collected in June, August, October, and March for measurement of APA. In water from the pond, the greatest V-max of APA usually was associated with microorganisms in the size classes between 0.8-3 mu m. In mesocosm experiments, the N+P treatment increased V-max of dissolved and particulate associated APA in the 0.2-0.8 mu m size range and in dissolved form. The V-max of APA in the largest size-fraction (> 3 mu m) increased markedly with P deficiency (+N treatment) and decreased in the P-enrichment treatment. The patterns of APA and chlorophyll associated with different size fractions often varied independently among different treatments and seasons and not always as a function of P deficiency, indicating the difficulty of attempting to normalize APA to phytoplankton biomass or chlorophyll. The Michaelis half saturation constant of APA in the pond water showed no strong trends with varied seasons or size fraction.

Protein phosphatase inhibition assay for detection of diarrhetic shellfish poison in oyster

A method based on protein phosphatase enzyme activity inhibition for the detection of diarrhetic shellfish poison (DSP) was used to analyze the DSP toxicity in three oyster samples. Based on the standard dose-effect curve developed with a series of okadaic acid (OA) standard solutions, the DSP toxicity of the three oyster samples collected were screened, and the results showed that there were no OA and dinophysis toxins ( DTXs) in the samples without hydrolization. However, the OA toxicity could be detected in two of the hydrolyzed samples, and the OA toxicity of the two samples were 1.81 and 1.21 mu g OA eq./kg oyster, respectively.

Total synthesis of bis-(2,3-dibromo-4,5-dihydroxyphenyl)-methane as potent PTP1B inhibitor

Protein tyrosine phosphatase 1B (PTP1B) plays an important role as a negative regulator and has been proved to be an effective target for the treatment of type 2 diabetes mellitus. Bis-(2,3-dibromo-4,5-dihydroxyphenyl)-methane 7 was first reported as a natural bromophenol with significant inhibition against PTP1B which was isolated from red algae Rhodomela confervoides. Intrigued by its astonishing activity (IC50 = 2.4 mu mol/L), compound 7 was synthesized with the overall yield of 24% and evaluated for its PTP1B inhibitory activity compared with natural compound. (C) 2008 Li Jun Han. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.