Phytoplankton and bacterial alkaline phosphatase activities in relation to phosphate and DOP availability within the Gironde plume waters (Bay of Biscay)

Previous studies conducted on the continental shelf in the Southeast Bay of Biscay influenced by Gironde waters (one of the two largest rivers on the French Atlantic coast) showed the occurrence of late winter phytoplankton blooms and phosphorus limitation of algal growth thereafter. In this context, the importance of dissolved organic phosphorus (DOP) for both algae and bacteria was investigated in 1998 and 1999 in terms of stocks and fluxes. Within the mixed layer, although phosphate decreased until exhaustion from winter to spring, DOP remained high and phosphate monoesters made up between 11 to 65% of this pool. Total alkaline phosphatase activity (APA, V_max) rose gradually from winter (2-8 nM h⁻¹) to late spring (100-400 nM h⁻¹), which was mainly due to an increase in specific phytoplankton (from 0.02 to 3.0 nmol μgC⁻¹ h⁻¹) and bacterial APA (from 0.04 to 4.0 nmol μgC⁻¹ h⁻¹), a strategy to compensate for the lack of phosphate. At each season, both communities had equal competitive abilities to exploit DOP but, taking into account biomass, the phytoplankton community activity always dominated (57-63% of total APA) that of bacterial community (9-11%). The dissolved APA represented a significant contribution. In situ regulation of phytoplanktonic APA by phosphate (induction or inversely repression of enzyme synthesis) was confirmed by simultaneously conducted phosphate-enrichment bioassays. Such changes recorded at a time scale of a few days could partly explain the seasonal response of phytoplankton communities to phosphate depletion.     

Modulatory influence of Adhatoda vasica Nees leaf extract against gamma irradiation in Swiss albino mice

The radiomodulatory influence of ethanolic extract of Adhatoda vasica Nees leaf extract against radiation-induced hematological alterations in peripheral blood of Swiss albino mice was studied at various post-irradiation intervals between 6 h to 30 days. Oral administration of A. vasica leaf extract (800 mg/kg body weight) prior to whole body irradiation showed a significant protection in terms of survival percentage and hematological parameters. Mice exposed to radiation (8.0 Gy) without A. vasica leaf extract pre-treatment exhibited signs of radiation sickness like anorexia, lethargicity, ruffled hairs and diarrhoea and such animals died within 25 days post-irradiation. The dose reduction factor (DRF = 1.6) for A. vasica leaf extract was calculated from LD50/30 values. A significant decline in hematological constituents (RBCs, WBCs, Hb and Hct) was evident till day 15 and no animal could survive beyond day 25. Conversely, animals pre-treated with A. vasica leaf extract showed 81.25% survival till 30 days after exposure and a gradual recovery was noted in the hematological values. However, these hematological values remained significantly below the normal even till day 30. A significant decrease in blood reduced glutathione (GSH) content and increase in lipid peroxidation (LPO) level was observed in control animals (Radiation alone). However, A. vasica leaf extract pretreated irradiated animals exhibited a significant increase in GSH content and decrease in LPO level. A significant increase in the serum alkaline phosphatase activity and decrease in acid phosphatase activity was observed in A. vasica leaf extract pretreated irradiated animals during the entire period of study.     

Ectopic expression of GmPAP3 alleviates oxidative damage caused by salinity and osmotic stresses

The primary biochemical reaction of purple acid phosphatases (PAP) is to catalyze the hydrolysis of phosphate esters and anhydrides. However, the soybean GmPAP3 gene expression is induced by NaCl, osmotic, and oxidative treatments, indicating a possible role of PAP in abiotic stress responses. Confocal and electron microscopic studies demonstrated that GmPAP3 protein is mainly localized in mitochondria, a primary site for reactive oxygen species (ROS) production. When subjected to NaCl and polyethylene glycol (PEG) treatments, ectopic expression of GmPAP3 in transgenic tobacco BY-2 cells mimicked the protective effects exhibited by the antioxidant ascorbic acid: increase in the percentage of cells with active mitochondria; reduction in the percentage of dead cells; and reduced accumulation of ROS. In addition, when GmPAP3 transgenic Arabidopsis thaliana seedlings were subjected to NaCl, PEG, and paraquat (PQ) treatments, the percentage of root elongation was significantly higher than the wild type. Furthermore, PQ-induced lipid peroxidation in these transgenic seedlings was also reduced. In summary, the mitochondrial localized GmPAP3 may play a role in stress tolerance by enhancing ROS scavenging.     

The trigonal-bipyramidal NO4 ligand set in biologically relevant vanadium compounds and their inorganic models

In the present focused review, vanadate-dependent haloperoxidases and vanadate-inhibited enzymes which catalyze the hydrolysis of phosphoester bonds are addressed. In these systems, vanadate [H_xVO₄]^(3−x)− is covalently coordinated to the imidazolyl moiety of an active site histidine, with a geometrical arrangement close to a trigonal bipyramid. The resulting ligand set, NO₄, and ligand arrangement provide peroxidase activity to the haloperoxidases and, to a certain extent, also to vanadate-inhibited phosphatases. The haloperoxidases are responsible for the oxidative halogenation of a variety of organic substrates. They are also active in other oxidation reactions relying on peroxide as the oxidant, such as the oxidative cyclizations of terpenes and, specifically, the oxygenation of (prochiral) sulfides to (chiral) sulfoxides. These functions can be modeled by vanadium complexes. Attracted interest is paid to {V(NO₄)} complexes that are functional and structural models of the peroxidases. In the vanadate-inhibited phosphatases – structural analogs of the transition state in phosphoester hydrolysis by the native enzymes – the position of the axial histidine can also be taken by cysteinate or serinate, a fact which has implications for the insulin-mimetic potential of vanadate.     

Responses of protein phosphatases and cAMP-dependent protein kinase in a freeze-avoiding insect, Epiblema scudderiana

Larvae of the goldenrod gall moth, Epiblema scudderiana, use the freeze avoidance strategy of winter cold hardiness and show multiple metabolic adaptations for subzero survival including accumulation of large amounts of glycerol as a colligative antifreeze. Induction and regulation of cold hardiness adaptations requires the intermediary action of signal transduction enzymes. Changes in the activities of several signaling enzymes including cAMP-dependent protein kinase (PKA), protein phosphatases 1 (PP1), 2A, 2C, and protein tyrosine phosphatases (PTPs) were monitored over the winter and during experimental exposures of larvae to subzero temperatures (-4 degrees C, a temperature that triggers rapid glycerol synthesis, or -20 degrees C, a common midwinter ambient temperature) or anoxia. A strong increase in the amount of active PP1 in the latter part of the winter may be responsible for shutting off glycogenolysis once glycerol levels are maximized. There appears to be a limited role for PKA in overwintering but PP2A and PP2C activities rose when larvae were exposed to -20 degrees C and PTP activities rose significantly over the winter months and also in response to laboratory subzero (-20 degrees C) and anoxia exposures. The strong responses by PTPs suggest that these may be involved in cell cycle and growth arrest during winter diapause.     

谷氨酸受体可逆磷酸化及其功能

谷氨酸受体(GluRs)C端区存在被多种蛋白激酶磷酸化的位点,同时又能被多种蛋白磷酸酶去磷酸化,磷酸化的结果可使Ca²⁺内流增加,增强GluRs功能;去磷酸化作用则相反.正常情况下GluRs可逆磷酸化处于一种动态平衡状态,在突触可塑性机制如长时程增强(LTP)中起重要作用,而在病理状态如缺血性脑损伤中,这种平衡失衡加重兴奋性神经元损伤.     

Characterization of the in vitro kinase activity of a partially purified soluble GST/JAK2 fusion protein

In vivo effects of insulin and vanadium treatment on glycogen synthase (GS), glycogen synthase kinase-3 (GSK-3) and protein phosphatase-1 (PP1) activity were determined in Wistar rats with streptozotocin (STZ)-induced diabetes. The skeletal muscle was freeze-clamped before or following an insulin injection (5 U/kg i.v.). Diabetes, vanadium, and insulin in vivo treatment did not affect muscle GSK-3 activity as compared to controls. Following insulin stimulation in 4-week STZ-diabetic rats muscle GS fractional activity (GSFA) was increased 3 fold (p < 0.05), while in 7-week diabetic rats it remained unchanged, suggesting development of insulin resistance in longer term diabetes. Muscle PP1 activity was increased in diabetic rats and returned to normal after vanadium treatment, while muscle GSFA remained unchanged. Therefore, it is possible that PP1 is involved in the regulation of some other cellular events of vanadium (other than regulation of glycogen synthesis). The lack of effect of vanadium treatment in stimulating glycogen synthesis in skeletal muscle suggests the involvement of other metabolic pathways in the observed glucoregulatory effect of vanadium.