Orthophosphate control of glucose-6-phosphate dehydrogenase light modulation in relation to the induction phase of chloroplast photosynthesis

High concentrations of orthophosphate (Pi) inhibited CO₂-dependent O₂ evolution and prevented the inactivation of glucose-6-P dehydrogenase by light in intact spinach and barley chloroplasts. Addition of glycerate-3-P to chloroplasts inhibited by Pi in the light, induced O₂ evolution and caused rapid inactivation of glucose-6-P dehydrogenase. The activity of phosphofructokinase detected in chloroplast preparations was not affected by light or by Pi.     

Effect of a modular extensive green roof on stormwater runoff and water quality

Runoff quantity and quality from a 248 m² extensive green roof and a control were compared in Connecticut using a paired watershed study. Weekly and individual rain storm samples of runoff and precipitation were analyzed for TKN, NO₃ + NO₂-N, NH₃-N, TP, PO₄-P, and total and dissolved Cu, Pb, Zn, Cd, Cr, and Hg. The green roof watershed retained 51.4% of precipitation during the study period based on area extrapolation. Overall, the green roof retained 34% more precipitation than predicted by the paired watershed calibration equation. TP and PO₄-P mean concentrations in green roof runoff were higher than in precipitation but lower than in runoff from the control. The green roof was a sink for NH₃-N, Zn, and Pb, but not for TP, PO₄-P, and total Cu. It also reduced the mass export of TN, TKN, NO₃ + NO₂-N, Hg, and dissolved Cu primarily through a reduction in stormwater runoff. Greater than 90% of the total Cu, Hg, and Zn concentrations in the green roof runoff were in the dissolved form. The growing media and slow release fertilizer were probable sources of P and Cu in green roof runoff. Overall, the green roof was effective in reducing stormwater runoff and overall pollutant loading for most water quality contaminants.     

Catabolism of d-fructose and d-ribose by Pseudomonas doudoroffii

1. The 1-P-fructokinase (1-PFK) and 6-P-fructokinase (6-PFK) from Pseudomonas doudoroffii were partially purified by a combination of (NH₄)₂SO₄ fractionation and DEAE-Sephadex column chromatography. The pH optima of these enzymes were 9.0 and 8.5, respectively.
2. When the concentrations of the substrates of the 1-PFK reaction were varied, Michaelis-Menten kinetics were observed. The Kms for d-fructose-1-P (F-1-P) and ATP were 3.03×10^-4 M and 3.39×10^-4 M, respectively. Variation of MgCl₂ at fixed concentrations of F-1-P and ATP resulted in sigmoidal kinetics; about 10 mM MgCl₂ was necessary for maximal activity. Activity of 1-PFK was inhibited when the ratio of ATP: Mg⁺⁺ was higher than 0.5, suggesting that ATP: 2Mg⁺⁺ was the substrate and that free ATP was inhibitory. Although an absolute requirement for K⁺ or NH ₊ ⁴ could not be demonstrated, these cations stimulated the rate of the reaction. Activity of 1-PFK was not significantly affected by 3 mM AMP, cyclic-AMP, P_i, d-fructose-6-P (F-6-P), ADP, P-enolpyruvate (PEP), pyruvate, citrate, or l-glutamate.
3. Sigmoidal kinetics were observed for 6-PFK when the concentration of F-6-P was increased and the level of ATP was kept constant. Activity of 6-PFK was increased by ADP, inhibited by PEP, and unaffected by 3 mM AMP, cyclic-AMP, P_i, F-1-P, pyruvate, or citrate.

     

Covalent modification of the solubilized rat liver vitamin K-dependent carboxylase with pyridoxal-5′-phosphate

The carboxylation of the pentapeptide substrate, Phe-Leu-Glu-Glu-Ile, by a rat microsomal vitamin K-dependent carboxylase was stimulated two- to threefold at pyridoxal-5′-P concentrations between 0.5 and 1.0 mm. This stimulation was reduced at concentrations higher than 1.0 mm. The K_m for the pentapeptide was lowered twofold in the presence of 1 mm pyridoxal-5′-P. The activation by pyridoxal-5′-P is specific, as 1 mm pyridoxal, pyridoxine, pyridoxine-5′-P, pyridoxamine, pyridoxamine-5′-P, or 4-pyridoxic acid did not stimulate the pentapeptide carboxylation rate. All six analogs, as well as formaldehyde and acetaldehyde, inhibited the carboxylation reaction in a concentration-dependent manner. The activation of the carboxylase by pyridoxal-5′-P appeared to be mediated by its direct binding to the enzyme via Schiff base formation. Sodium borohydride reduction of solubilized microsomes in the presence of pyridoxal-5′-P, followed by dialysis to remove unbound material, resulted in a carboxylase preparation with a specific activity twice that of the untreated control microsomes. The derivatized enzyme was not further stimulated by added pyridoxal-5′-P. This derivatized carboxylase could be obtained in the absence of pentapeptide and divalent cations. The stimulation of the carboxylase activity by divalent cations and pyridoxal-5′-P was mediated at separate site(s) on the enzyme. Studies of the NH₂-terminal pyridoxalated pentapeptide with both a normal and PLP-modified enzyme, in the presence and absence of PLP, demonstrated competition of the pentapeptide PLP moiety to a PLP site on the enzyme. It was concluded that pyridoxal-5′-P forms a covalent attachment to an ?-NH₂ of a lysine near the active site of the carboxylase.     

Human erythrocyte phosphoglycerate mutase: Evidence for normal catalysis in the absence of added 2,3-bisphospho-D-glycerate

Kinetic analyses indicate that human erythrocyte phosphoglycerate mutase catalyzes the normal, reversible isomerization of D-glycerate-3-P and D-glycerate-2-P in the absence of added D-glycerate-2,3-P₂. The reaction is impeded, however, by a potent inhibitor which occurs as a natural component of commericial D-glycerate-3-P. Inhibition may be overcome through substrate purification or by adding D-glycerate-2,3-P₂ to the reaction medium containing the contaminant. In surmounting the inhibition, bisphosphoglycerate performs as a non-essential activator and not as a cofactor. The latter concept is corroborated by the observation that D-glycerate-2,3-P₂ has absolutely no influence on mutase catalysis conducted in the presence of pure substrate. The data presented here and elsewhere, however, suggest that the red cell enzyme is readily phosphorylated by mono- as well as bisphosphoglycerate. Additional findings show that at concentrations in excess of 3mM, D-glycerate-3-P accelerates phosphoglycerate mutase catalysis in the absence of cofactor, suggesting that the mutase molecule possesses a normal catalytic site and an allosteric activator site.     

Phylogeny and ontogeny of the phosphoglycerate mutases.--V. Inactivation of phosphoglycerate mutase isozymes by histidine-specific reagents

1. The three isozymes of glycerate-2,3-P2 dependent phosphoglycerate mutase present in tissues of mammals and reptiles were inactivated by both treatment with diethylpyrocarbonate and photooxidation with rose bengal. 2. Inactivation of type M isozyme purified from rabbit muscle was complete when two histidine residues per enzyme subunit were carboethoxylated. Hydroxylamine removed the carboethoxy groups, with partial recovery of the enzymatic activity. The cofactor protected the enzyme against inactivation. 3. The inactivation of rabbit muscle phosphoglycerate mutase by photooxidation with methylene blue and rose bengal was sharply pH dependent. The pH profile of enzyme inactivation followed the titration curve of histidine, suggesting that this amino acid was critical for enzyme activity. Glycerate-2,3-P2 did not protect phosphoglycerate mutase against photoinactivation.     

Water quality of the Modder River,South Africa

The Modder River is a relatively small river in the central region of the Free State Province, South Africa and has a mean annual runoff of 184 × 106m³. Botshabelo is a city, which has developed in the catchment area of the river, and its sewage outflows are discharged into the Klein Modder, a tributary of the Modder River. This study was conducted in order to determine the influence of Botshabelo's sewage outflow on the water quality of the river. It was determined that the Modder and Klein Modder Rivers do not generally follow distinctive seasonal patterns in terms of chemical parameters, although NO₃-N and PO₄-P concentrations usually increase with increasing flow and conductivity decreases with increasing flow. Physical parameters such as turbidity, flow and temperature did however follow distinctive seasonal patterns from February 1996 to December 1997, as did phytoplankton growth. Low chlorophyll-a concentrations were exhibited in the winter and higher concentrations during spring. In the Klein Modder River, algal blooms occurred more frequently, and the algal biomass was higher than in the Modder River. This could be ascribed to the higher nutrient concentrations and lower flow velocities in the former. The inflow of the Klein Modder River into the Modder River caused on average, 112% increase in PO₄-P, 171% increase in NO₃-N, 50% increase in chlorophyll-a concentration, and 230% increase in E. coli counts.     

Photoinhibition of CO(2)-Dependent O(2) Evolution by Intact Chloroplasts Isolated from Spinach Leaves

Intact spinach (Spinacia oleracea L.) chloroplasts, when pre-illuminated at 4 millimoles quanta per square meter per second for 8 minutes in a CO₂-free buffer at 21% O₂, showed a decrease (30-70%) in CO₂-dependent O₂ evolution and ¹⁴CO₂ uptake. This photoinhibition was observed only when the O₂ concentration and the quantum fluence rate were higher than 4% and 1 millimole per square meter per second, respectively. There was only a small decrease in the extent of photoinhibition when the CO₂ concentration was increased from 0 to 25 micromolar during the treatment, but photoinhibition was abolished when the CO₂ concentration was increased to 30 micromolar. Addition of small quantities of P-glycerate (40-200 micromolar) or glycerate (160 micromolar) was found to prevent photoinhibition. Other intermediates of the Calvin cycle (fructose-6-P, fructose-1,6-P, ribose-5-P, ribulose-5-P) also prevented photoinhibition to various extents. Oxaloacetate was not effective in preventing photoinhibition in these chloroplasts. The amount of O₂ evolved during treatments with 3-P-glycerate or glycerate was no more than 65% of that measured in the presence of low CO₂ concentrations (9-12 micromolar) which did not prevent photoinhibition. In all cases, the extent to which photoinhibition was prevented by these metabolites was not correlated to the amount of O₂ evolved during the photoinhibitory treatment. It is concluded that in these chloroplasts the prevention of the O₂-dependent photoinhibition of light saturated CO₂ fixation capacity is not linked to the dissipation of excitation energy via the photosynthetic electron transport nor to ATP utilization. The requirement of O₂ for photoinhibition of CO₂ fixation capacity in isolated chloroplasts may be explained by an effect of O₂ in allowing metabolic depletion of Calvin cycle intermediates.     

FACTORS REGULATING THE SPATIAL DISTRIBUTION OF THE FILAMENTOUS ALGA PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) IN AN INDIANA LAKE1

Pithophora oedogonia (Mont.) Wittr. biomass in Surrey Lake, Indiana was greater in the littoral than in the pelagial region. Although mean soluble reactive phosphorus concentrations did not differ between the two areas, nitrate concentrations were almost six times higher in the cove than in the open water. Using laboratory cultures of Pithophora, the half saturation constant (K_s at 20° C relating filament growth to external concentrations of nitrate-nitrogen was determined to be 1.23 mg L^?1 (=88 μM)and for phosphate-phosphorus, 0.1 mg L^?1 (=3.22 μM). These values were used to calculate a NO₃-N/PO₄-P atomic ratio of 27.6. Comparison of this value with NO₃-N/PO₄-P ratios in Surrey Lake showed that nitrogen limiting conditions were prevalent in the open water section of the lake. Alkaline phosphatase and dark ammonia uptake analyses on field collected filaments from the shallow and deep water sections confirmed the hypothesis that nitrate is the major factor limiting growth of Pithophora in Surrey Lake.     

Phosphorus-31 relaxation times of 2,3-diphosphoglycerate in intact human erythrocytes

The reciprocals of the spin-lattice relaxation times (T₁s) of the 2-P and 3-P nuclei of 2,3-diphosphoglycerate (DPG) increased linearly as percent DPG bound was raised in model hemoglobin solutions. The 2-P T₁ was slightly greater in intact erythrocytes than in model solutions under similar experimental conditions. The change in the 3-P T₁ with cellular deoxygenation was anomalous indicating that this nucleus should not be used to estimate DPG binding inside intact erythrocytes.     

Phylogeny and ontogeny of the phosphoglycerate mutases - III. Inactivation of rabbit muscle phosphoglycerate mutase (type M isozyme) by the sulfhydryl group reagents

1. The three phosphoglycerate mutase isozymes from mammals (types M, B and MB isozymes) differ in their sensitivity to the - SH group reagents. 2. Rabbit muscle phosphoglycerate mutase (type M isozyme) is reversibly inactivated by tetrathionate, rho-chloromercuribenzoate and Hg2+. 3. Titration with rho-chloromercuribenzoate shows the existence of two sulfhydryl groups per enzyme subunit, the modification of which produces a progressive decline in enzyme activity. 4. The apparent Km values for substrate and cofactor are not affected by tetrathionate treatment. 5. Phosphoglycerate mutase inactivated by tetrathionate and by rho-chloromercuribenzoate is unable to form the functionally active phosphorylenzyme when mixed with glycerate-2,3-P2, and is not protected by the cofactor against heating. 6. Glycerate-2,3-P2 protects against tetrathionate treatment, but fails to protect against Hg2+ and rho-chloromercuribenzoate inactivation.     

九龙江河口区养虾塘沉积物-水界面营养盐交换通量特征

通过对九龙江河口区陆基养虾塘水样和沉积物样品采集分析及结合室内模拟实验,探讨了虾塘在不同养殖阶段沉积物-水界面营养盐通量时间变化特征及其主要影响因素。虾塘沉积物向上覆水体释放NO_x~--N(NO_2~--N和NO_3~--N)、NH_4~+-N和PO_4~(3-)-P能力均呈现随养殖时间推移而降低的特征。沉积物在养殖中期和后期分别呈现对上覆水体NO_x~--N和PO_4~(3-)-P的吸收现象,但总体表现为释放(平均通量分别为(1.87±1.15)、(1.58±0.52)mg m~(-2)h~(-1)和(1.22±0.62)mg m~(-2)h~(-1))。沉积物-水界面溶解无机氮交换以NH_4~+-N为主(沉积物平均释放通量为(46.18±13.82)mg m~(-2)h~(-1))。沉积物间隙水与上覆水间的营养盐浓度差(梯度)及温度对上述交换通量的时间动态特征具有重要调控作用。研究结果表明养殖初期或中期沉积物较高的无机氮(尤其是NO_2~--N和NH_4~+-N)释放是养殖塘水质恶化的一个极具潜力的污染内源,可能会对虾的健康生长产生负面效应,控制沉积物无机氮释放是养虾塘养殖初期和中期重要的日常管理活动之一。     

The Compartmentalisation of Phosphorylated Free Oligosaccharides in Cells from a CDG Ig Patient Reveals a Novel ER-to-Cytosol Translocation Process

Background

Biosynthesis of the dolichol linked oligosaccharide (DLO) required for protein N-glycosylation starts on the cytoplasmic face of the ER to give Man₅GlcNAc₂-PP-dolichol, which then flips into the ER for further glycosylation yielding mature DLO (Glc₃Man₉GlcNAc₂-PP-dolichol). After transfer of Glc₃Man₉GlcNAc₂ onto protein, dolichol-PP is recycled to dolichol-P and reused for DLO biosynthesis. Because de novo dolichol synthesis is slow, dolichol recycling is rate limiting for protein glycosylation. Immature DLO intermediates may also be recycled by pyrophosphatase-mediated cleavage to yield dolichol-P and phosphorylated oligosaccharides (fOSGN2-P). Here, we examine fOSGN2-P generation in cells from patients with type I Congenital Disorders of Glycosylation (CDG I) in which defects in the dolichol cycle cause accumulation of immature DLO intermediates and protein hypoglycosylation.

Methods and Principal Findings

In EBV-transformed lymphoblastoid cells from CDG I patients and normal subjects a correlation exists between the quantities of metabolically radiolabeled fOSGN2-P and truncated DLO intermediates only when these two classes of compounds possess 7 or less hexose residues. Larger fOSGN2-P were difficult to detect despite an abundance of more fully mannosylated and glucosylated DLO. When CDG Ig cells, which accumulate Man₇GlcNAc₂-PP-dolichol, are permeabilised so that vesicular transport and protein synthesis are abolished, the DLO pool required for Man₇GlcNAc₂-P generation could be depleted by adding exogenous glycosylation acceptor peptide. Under conditions where a glycotripeptide and neutral free oligosaccharides remain predominantly in the lumen of the ER, Man₇GlcNAc₂-P appears in the cytosol without detectable generation of ER luminal Man₇GlcNAc₂-P.

Conclusions and Significance

The DLO pools required for N-glycosylation and fOSGN2-P generation are functionally linked and this substantiates the hypothesis that pyrophosphatase-mediated cleavage of DLO intermediates yields recyclable dolichol-P. The kinetics of cytosolic fOSGN2-P generation from a luminally-generated DLO intermediate demonstrate the presence of a previously undetected ER-to-cytosol translocation process for either fOSGN2-P or DLO.     

HPLC separation and indirect ultraviolet detection of phosphorylated sugars

An HPLC method for the separation and analysis of phosphorylated sugars is presented. Ion-exchange chromatography coupled to indirect ultraviolet detection has produced good resolution and sensitivity. Fructose 6-P, glucose 6-P, ribose 5-P, 3-phosphoglyceric acid, ribulose 1,5-P₂, fructose 1,6-P₂, and sedoheptulose 1,7-P₂ can be separated at a sensitivity down to 10 nanomoles. The system resolves 2-carboxy-D-arabinitol 1,5-P₂ from 2-carboxy-D-ribitol 1,5-P₂. The natural inhibitor of ribulose bisphosphate carboxylase, 2-carboxy-D-arabinitol 1-P, has been separated from its 5-P isomer and most other phosphorylated compounds. This method is applied to identification of the products obtained upon ion-exchange purification of synthetic 2-carboxyarabinitol 1-P.     

Sphingosine 1-Phosphate (S1P) Receptor Agonists Mediate Pro-fibrotic Responses in Normal Human Lung Fibroblasts via S1P2 and S1P3 Receptors and Smad-independent Signaling

Synthetic sphingosine 1-phosphate receptor 1 modulators constitute a new class of drugs for the treatment of autoimmune diseases. Sphingosine 1-phosphate (S1P) signaling, however, is also involved in the development of fibrosis. Using normal human lung fibroblasts, we investigated the induction of fibrotic responses by the S1P receptor (S1PR) agonists S1P, FTY720-P, ponesimod, and SEW2871 and compared them with the responses induced by the known fibrotic mediator TGF-β1. In contrast to TGF-β1, S1PR agonists did not induce expression of the myofibroblast marker α-smooth muscle actin. However, TGF-β1, S1P, and FTY720-P caused robust stimulation of extracellular matrix (ECM) synthesis and increased pro-fibrotic marker gene expression including connective tissue growth factor. Ponesimod showed limited and SEW2871 showed no pro-fibrotic potential in these readouts. Analysis of pro-fibrotic signaling pathways showed that in contrast to TGF-β1, S1PR agonists did not activate Smad2/3 signaling but rather activated PI3K/Akt and ERK1/2 signaling to induce ECM synthesis. The strong induction of ECM synthesis by the nonselective agonists S1P and FTY720-P was due to the stimulation of S1P₂ and S1P₃ receptors, whereas the weaker induction of ECM synthesis at high concentrations of ponesimod was due to a low potency activation of S1P₃ receptors. Finally, in normal human lung fibroblast-derived myofibroblasts that were generated by TGF-β1 pretreatment, S1P and FTY720-P were effective stimulators of ECM synthesis, whereas ponesimod was inactive, because of the down-regulation of S1P₃R expression in myofibroblasts. These data demonstrate that S1PR agonists are pro-fibrotic via S1P₂R and S1P₃R stimulation using Smad-independent pathways.     

Citrate inhibition of rat-kidney cortex phosphofructokinase

The regulatory properties of citrate on the activity of phosphofructokinase (PFK) purified from rat-kidney cortex has been studied. Citrate produces increases in the K_0.5 for Fru-6-P and in the Hill coefficient as well as a decrease in the V_max of the reaction without affecting the kinetic parameters for ATP as substrate. ATP potentiates synergistically the effects of citrate as an inhibitor of the enzyme. Fru-2,6-P₂ and AMP at concentrations equal to K_a were not able to completely prevent citrate inhibition of the enzyme. Physiological concentrations of ATP and citrate produce a strong inhibition of renal PFK suggesting that may participate in the control of glycolysisin vivo.Abbreviations PFK 6-Phosphofructo-1-kinase (EC 2.7.1.11) - Fru-6-P Fructose 6-phosphate - Fru-2,6-P₂ Fructose 2,6-bisphosphate     

Influence of nitrogen species (NH4 + and NO3 −) on the dynamics of P in water–sediment–Salvinia herzogii systems

Water – Salvinia herzogii – sediment systems were exposed to different phosphorus and nitrogen combinations in outdoor experiments. The aim was to estimate the amounts of P immobilized in macrophytes and sediments, as well as to elucidate whether or not the presence of N affects the retention of P. The following components were added: o-P, o-P + NH₄ ⁺, o-P + NO₃ ^– + NH₄ ⁺, o-P + NO₃ ^–. The concentration of nutrients was periodically determined throughout the experiment (28 days). The concentrations of P and N in plant tissues and sediments were determined at the beginning and the end of the experiment. Sequential extractions of P-fractions in sediment were performed using the EDTA method (Golterman, 1996). The removal efficiency of P in water was 95–99%. The removal of NH₄ ⁺ (97–98%) was more effective than that of NO₃ ^– (44–86%). The presence of nitrogen species increased the removal velocity of o-P from water, NH₄ ⁺ was the most effective species. Sediments not only had higher P removal rates than macrophytes but, in the control treatment without macrophytes, they reached the values obtained by macrophytes plus sediments in the other treatments. The adsorption of P takes place at the surface layer of the sediment (1 cm). Most of the P incorporated into the sediment during the experiment was sorbed by the fraction Fe(OOH)P. The addition of nutrients to water modified the leaves/lacinias weight ratio.     

Spatial pattern and variability in soil N and P availability under the influence of two dominant species in a pine forest

The presence of a legume in a nitrogen (N)-limited forest ecosystem may not only create ??islands of N fertility?? but also affect the phosphorus (P) availability. The main objective of this study was to compare the effect of a pine (Pinus canariensis) and a leguminous (Adenocarpus viscosus) species on the spatial pattern and variability of different labile organic-N (microbial biomass-N [MB-N] and dissolved organic-N [DON]), as well as inorganic-N (IN) and ?CP fractions (NH₄-N, NO₃-N, and PO₄-P), in a forest soil of the Canary Islands (Spain). Assuming some litter quantity and quality differences between these two species, we expected to find higher soil labile organic-N concentrations under isolated individuals of P. canariensis than under isolated individuals of A. viscosus. We also expected to find higher concentrations and spatial dependence (percentage of total variance explained by spatial autocorrelation) of NO₃-N beneath A. viscosus than beneath P. canariensis canopies, and higher spatial scaling of soil variables under the influence of P. canariensis canopies than under the presence of A. viscosus individuals. Moreover, we tested whether the soil variables measured under isolated individuals of both species showed a different spatial variability than the same soil variables measured under overlapping pine canopies inside a pine forest. To test these hypotheses, soil samples under isolated mature individuals of each species were collected in the winter and summer, whereas under a pine forest canopy, the sampling was performed only in the winter. The winter MB-N and DON concentrations were significantly higher beneath the pine individual, whereas the winter NO₃-N, NO₃-N-to-IN ratio, and PO₄-P were significantly higher under the leguminous individual; these differences were not observed in the summer samples. We found higher spatial ranges under the pine than under the legume canopy in the winter sampling, and the spatial dependence of NO₃-N was twice as high beneath the legumes as under the pines at both sampling dates. The soil spatial variability was higher (up to 17 times higher) under isolated individuals than inside the pine forest. The results of this study suggest that both the morphological and physiological characteristics of P. canariensis and A. viscosus, as well as the spatial pattern of P. canariensis, may influence the spatial pattern and variability of soil resources.     

Effects of phosphate-solubilizing bacteria application on soil phosphorus availability in coal mining subsidence area in Shanxi

The effect of phosphate-solubilizing bacteria (PSB) application on phosphorus (P) availability in reclaimed soil in coal mining subsidence region was investigated. Seven treatments were carried out including control, chicken manure (CM), PSB, PSB + tricalcium phosphate (TCP), CM?+?TCP, PSB?+?ground phosphate rock (GPR) and CM?+?GPR. The results showed soil Olsen-P concentration and phosphatase level as well as the yield of pakchoi (Brassica chinensis L.) were significantly higher in PSB application treatments compared to the corresponding CM application treatments. Soil phosphatase, invertase and urease contents were increased most significantly in PSB treatment, 1.18-, 1.31- and 2.32-fold higher than those in the control, respectively. Soil Ca₂-P, Ca₈-P, Fe-P and Al-P concentrations exhibited the greatest increases in PSB?+?TCP treatment, while occluded-P showed minor changes in different treatments. Application of PSB fertilizer reduced the transformation of Olsen-P to Ca₁₀-P, thus increasing P availability in reclaimed soil of coal mining subsidence area.     

Enzyme regulation in c(4) photosynthesis : identification and localization of activities catalyzing the synthesis and hydrolysis of fructose-2,6-bisphosphate in corn leaves

Activities catalyzing the synthesis of fructose-2,6-bisphosphate (fructose-6-phosphate,2-kinase or Fru-6-P,2K) and its breakdown (fructose-2,6-bisphosphatase or Fru-2,6-P₂ase) were identified in leaves of corn (Zea mays), a C₄ plant. Fru-6-P,2K and Fru-2,6-P₂ase were both localized mainly, if not entirely, in the leaf mesophyll cells. A partially purified preparation containing the two activities revealed that the kinase and phosphatase were regulated by metabolite effectors in a manner generally similar to their counterparts in C₃ species. Thus, corn Fru-6-P,2K was activated by inorganic phosphate (Pi) and fructose-6-phosphate, and was inhibited by 3-phosphoglycerate and dihydroxyacetone phosphate. Fru-2,6-P₂ase was inhibited by its products, fructose-6-phosphate and Pi. However, unlike its spinach equivalent, corn Fru-2,6-P₂ase was also inhibited by 3-phosphoglycerate and, less effectively, by dihydroxyacetone phosphate. The C₄ Fru-6-P,2K and Fru-2,6-P₂ase were also quite sensitive to inhibition by phosphoenolpyruvate, and each enzyme was also selectively inhibited by certain other metabolites.