Rate Of Phosphate Release Research Articles

Phosphate Release Kinetics in Calcareous Grassland and Forest Soils in Response to H+Addition

Phosphate release kinetics in soils are of global interest because sustainable plant nutrition with phosphate will be a major concern in the future. Dissolution of phosphate-containing minerals induced by a changing rhizosphere equilibrium through proton input is one important mechanism that releases phosphate into bioavailable forms. Our objectives were (i) to determine phosphate release kinetics during H+ addition in calcareous soils of the Schwabische Alb, Germany, and to assess the influence of (ii) land-use type (grassland vs. forest) and (iii) management intensity on reactive phosphate pools and phosphate release rate constants during H+ addition. Phosphate release kinetics were characterized by a large fast-reacting phosphatepool, which could be attributed to poorly-crystalline calcium phosphates, and a small slow-reacting phosphate pool probably originating from carbonate-bearing hydroxylapatite. Both reactive phosphate pools—as well as total phosphate concentrations (TP) in soil—were greater in grassland than in forest soils. In organically fertilized grassland soils, concentrations of released phosphate were higher than in unfertilized soils, likely because organic fertilizers contain poorly-crystalline phosphate compounds which are further converted into sparingly soluble phosphate forms. Because of an enriched slow-reacting phosphate pool, mown pastures were characterized by a more continuous slow phosphate release reaction in contrast to clear biphasic phosphate release patterns in meadows. Consequently, managing phosphate release kinetics via management measures is a valuable tool to evaluate longer-term P availability in soil in the context of finite rock phosphate reserves on earth.

Kinetic Characterization of the ATPase and Actin-activated ATPase Activities of Acanthamoeba castellanii Myosin-2

Phosphorylation of Ser-639 in loop-2 of the catalytic motor domain of the heavy chain of Acanthamoeba castellanii myosin-2 and the phosphomimetic mutation S639D have been shown previously to down-regulate the actin-activated ATPase activity of both the full-length myosin and single-headed subfragment-1 (Liu, X., Lee, D. Y., Cai, S., Yu, S., Shu, S., Levine, R. L., and Korn, E. D. (2013) Proc. Natl. Acad. Sci. U.S.A. 110, E23-E32). In the present study we determined the kinetic constants for each step in the myosin and actomyosin ATPase cycles of recombinant wild-type S1 and S1-S639D. The kinetic parameter predominantly affected by the S639D mutation is the actin-activated release of inorganic phosphate from the acto myosin·ADP·Pi complex, which is the rate-limiting step in the steady-state actomyosin ATPase cycle. As consequence of this change, the duty ratio of this conventional myosin decreases. We speculate on the effect of Ser-639 phosphorylation on the processive behavior of myosin-2 filaments.

Modeling hydrolysis of slowly biodegradable organic compounds in biological nutrient removal activated sludge systems

Hydrolysis is an important process in biological wastewater treatment and is known to be the rate-limiting step in organic carbon removal from municipal or industrial wastewater. The influence of the readily biodegradable chemical oxygen demand fraction in biological wastewater treatment systems has been extensively investigated, but little is known about the effects of slowly biodegradable substrate (XS) on denitrification and enhanced biological phosphorus removal. The biodegradation of XS is initiated by hydrolysis, which is an integral part of activated sludge models, such as the Activated Sludge Model no. 2d (ASM2d). This process is slower than heterotrophic growth and thus becomes the rate-limiting step for the biodegradation of organic compounds. The aim of this study was to evaluate different concepts of modeling the hydrolysis process using the original and modified version of ASM2d. Batch test results obtained at a large biological nutrient removal (BNR) plant in Gdansk (Poland) provided an experimental database for comparison of the two model predictions. Both models were compared in terms of their predictions for the most important process rates in BNR activated sludge systems. In comparison with the orginal ASM2d, the modified model had no or only minor effect on the predicted nitrate utilization rate, phosphate release rate and anoxic/aerobic phosphate uptake rate, but better predicted the oxygen uptake rate. The average ARDs (average relative deviations) were 19.0 and 29.3% (original ASM2d) vs. 13.4 and 20.4% (modified ASM2d), respectively, for the settled wastewater without pretreatment and after coagulation-flocculation.

Yeast Pif1 Helicase Exhibits a One-base-pair Stepping Mechanism for Unwinding Duplex DNA

Kinetic analysis of the DNA unwinding and translocation activities of helicases is necessary for characterization of the biochemical mechanism(s) for this class of enzymes. Saccharomyces cerevisiae Pif1 helicase was characterized using presteady state kinetics to determine rates of DNA unwinding, displacement of streptavidin from biotinylated DNA, translocation on single-stranded DNA (ssDNA), and ATP hydrolysis activities. Unwinding of substrates containing varying duplex lengths was fit globally to a model for stepwise unwinding and resulted in an unwinding rate of ∼75 bp/s and a kinetic step size of 1 base pair. Pif1 is capable of displacing streptavidin from biotinylated oligonucleotides with a linear increase in the rates as the length of the oligonucleotides increased. The rate of translocation on ssDNA was determined by measuring dissociation from varying lengths of ssDNA and is essentially the same as the rate of unwinding of dsDNA, making Pif1 an active helicase. The ATPase activity of Pif1 on ssDNA was determined using fluorescently labeled phosphate-binding protein to measure the rate of phosphate release. The quantity of phosphate released corresponds to a chemical efficiency of 0.84 ATP/nucleotides translocated. Hence, when all of the kinetic data are considered, Pif1 appears to move along DNA in single nucleotide or base pair steps, powered by hydrolysis of 1 molecule of ATP.

Preparation of pH-Sensitive Polymers/Layered Double Hydroxide Hybrid Beads for Controlled Release of Insulin

The present work introduces new hybrid material based on the combination of layered double hydroxides (LDH) and a pH-sensitive polymer (PSP), alginate, a polysaccharide widely applied for encapsulating drugs to produce a LDH–polymer nanocomposite, able to act as an effective drug delivery system (DDS) in comparison to the Zn–Al LDH or the polymer alone. Insulin has been chosen as a model drug, being loaded in a Zn–Al LDH matrix. In vitro release profiles were established separately in both the presence and absence of glucose phosphate in pH 7. Drug release studies showed that the in the presence of glucose phosphate release rate increases.

The Affect of Omecamtiv Mecarbilon the Phosphoate Dissociation and Motile Properties of the Recombinant Human β-Cardiac Heavymeromyosin

Omecamtiv mecarbil (OM), a small-molecule increases cardiac contractility by directly activating cardiac myosin by accelerating phosphate (Pi) release (Malik et al., 2011). Here we analyzed the affect of OM on the mechanochemical cycle and motility of human β-cardiac heavymeromyosin expressed in a adenoviral/C2C12 muscle cell based system, and purified porcine ventricular myosin (PV-HMM). Double-mixing stopped-flow fluorescence and phosphate binding protein (MDCC-PBP) were used to determine the maximum rate (kmax) of phosphate release. Rates of 30s−1 and 35s−1 were obtained for human and porcine cardiac HMM respectively. Addition of 20 µM OM resulted in a 2-fold increase in the maximal rate of actin activated Pi release to kmax = 70 s−1 (AM-ADP-Pi _> AM-ADP + Pi) for both human and porcine cardiac HMM. The unloaded actin filament velocity measured in the in vitro motility assay was 0.76 ± 0.37 µm/sec for human β-cardiac HMM and 0.97 ± 0.23 µm/sec for PV-HMM. OM has two effects on the motor activity: 1) The actin filament velocity was significantly slower (∼ 16 -fold at saturation); 2) the filament motion became more persistent with long periods of uninterrupted movement. This suggests that OM recruits more crossbridges to participate in the movement of the actin filaments resulting in higher forces per filament, which overcomes the pinning defects that invariably trap actin filaments in normal motility assays. The increase in attached crossbridges/filament also slows the filament velocity. The motility data are consistent with the kinetic analysis indicating that OM accelerates Pi release without dramatically enhancing the rate of the ATPase hydrolysis. This produces a higher duty ratio in which the motor spends more of the ATPase cycle in tight binding states. Supported by AHA-BGIA to EF and AHA-GI to DAW.

Suppression of phosphate release from coastal sediments using granulated coal ash

In order to evaluate suppression of phosphate release from sea bottom sediments using granulated coal ash (GCA), a byproduct from coal thermal electric power stations, field experiments were carried out at oyster culture sites where the sediments are rich in organic matter. Two types of GCA with the diameter of <40 mm were applied on separate bottom sediment plots of 50 m × 75 m with ca. 20 cm depth each. The first GCA type is composed of pulverized coal combustion ash (ExpA) and another consists of pressurized fluidized bed combustion ash (ExpB). Sediment pH was increased up to ca. 8.5 in both experimental plots due to hydrolysis of CaO. Phosphate concentration in the interstitial water of the sediment was significantly decreased in ExpA due to adsorption onto the GCA. A numerical model to quantify chemical and biological processes in the sediment was applied to estimate how phosphorus cycle was changed due to the application of GCA. The model output showed that release rate of phosphate from the sediment at ExpB was suppressed to the level of about 1 order lower (400 μmol m−3 d−1) than that in the control site (4800 μmol m−3 d−1), whereas decomposition of detrital phosphorus in the experimental site was estimated to have been enhanced 4.8 times compared to the control site. Considering both laboratory and simulated field experiments carried out previously, it was proven in the present study that GCA can effectively adsorb phosphate from interstitial water in organically enriched sediments and suppress the release of phosphate from the sediments to the upper water column in the field experiments.

Stretch of Contracting Cardiac Muscle Abruptly Decreases the Rate of Phosphate Release at High and Low Calcium

The contractile performance of the heart is linked to the energy that is available to it. Yet, the heart needs to respond quickly to changing demands. During diastole, the heart fills with blood and the heart chambers expand. Upon activation, contraction of cardiac muscle expels blood into the circulation. Early in systole, parts of the left ventricle are being stretched by incoming blood, before contraction causes shrinking of the ventricle. We explore here the effect of stretch of contracting permeabilized cardiac trabeculae of the rat on the rate of inorganic phosphate (P(i)) release resulting from ATP hydrolysis, using a fluorescent sensor for P(i) with millisecond time resolution. Stretch immediately reduces the rate of P(i) release, an effect observed both at full calcium activation (32 μmol/liter of Ca(2+)), and at a physiological activation level of 1 μmol/liter of Ca(2+). The results suggest that stretch redistributes the actomyosin cross-bridges toward their P(i)-containing state. The redistribution means that a greater fraction of cross-bridges will be poised to rapidly produce a force-generating transition and movement, compared with cross-bridges that have not been subjected to stretch. At the same time stretch modifies the P(i) balance in the cytoplasm, which may act as a cytoplasmic signal for energy turnover.

Rare, Nonsynonymous Variant in the Smooth Muscle-Specific Isoform of Myosin Heavy Chain, MYH11 , R247C, Alters Force Generation in the Aorta and Phenotype of Smooth Muscle Cells

Mutations in myosin heavy chain (MYH11) cause autosomal dominant inheritance of thoracic aortic aneurysms and dissections. At the same time, rare, nonsynonymous variants in MYH11 that are predicted to disrupt protein function but do not cause inherited aortic disease are common in the general population and the vascular disease risk associated with these variants is unknown. To determine the consequences of the recurrent MYH11 rare variant, R247C, through functional studies in vitro and analysis of a knock-in mouse model with this specific variant, including assessment of aortic contraction, response to vascular injury, and phenotype of primary aortic smooth muscle cells (SMCs). The steady state ATPase activity (actin-activated) and the rates of phosphate and ADP release were lower for the R247C mutant myosin than for the wild-type, as was the rate of actin filament sliding in an in vitro motility assay. Myh11(R247C/R247C) mice exhibited normal growth, reproduction, and aortic histology but decreased aortic contraction. In response to vascular injury, Myh11(R247C/R247C) mice showed significantly increased neointimal formation due to increased SMC proliferation when compared with the wild-type mice. Primary aortic SMCs explanted from the Myh11(R247C/R247C) mice were dedifferentiated compared with wild-type SMCs based on increased proliferation and reduced expression of SMC contractile proteins. The mutant SMCs also displayed altered focal adhesions and decreased Rho activation, associated with decreased nuclear localization of myocardin-related transcription factor-A. Exposure of the Myh11(R247C/R247C) SMCs to a Rho activator rescued the dedifferentiated phenotype of the SMCs. These results indicate that a rare variant in MYH11, R247C, alters myosin contractile function and SMC phenotype, leading to increased proliferation in vitro and in response to vascular injury.

Phosphorus release and uptake during start-up of a covered and non-aerated sequencing batch reactor with separate feeding of VFA and sulfate

This study explored a sulfur cycle-associated biological phosphorus (P) removal process in a covered and non-aerated sequencing batch reactor (SBR) fed with volatile fatty acid (VFA) and sulfate separately. During the 60-day start-up, both phosphate release and uptake rates increased, while poly-phosphate cyclically increased and decreased accordingly. The P-release and P-uptake rates were associated with VFA uptake and sulfate reduction. The average ratio of potassium to phosphate during the P-uptake and P-release was also determined to be 0.29-0.31 mol K/mol P, which is close to a reported value (0.33) for biological phosphorus removal. All this evidence confirmed there was biological P removal in this reactor, in which metabolism could be different from conventional biological P removal.

Efficient coupling of ATP hydrolysis to translocation by RecQ helicase

Helicases are ubiquitous enzymes that unwind double-stranded DNA (dsDNA) to reveal single-stranded DNA (ssDNA) during essential processes such as replication, transcription, or repair. The Escherichia coli RecQ protein is a 3' to 5' helicase, which functions in the processes of homologous recombination and replication fork restart. Here, we analyzed the relationship between ATP hydrolysis by RecQ and its translocation on ssDNA. We monitored a single round of RecQ translocation on ssDNA by measuring the rates of inorganic phosphate release during translocation, and the dissociation of RecQ from ssDNA. We find that RecQ translocates with a rate of 16( ± 4) nucleotides/s and moves on average only 36( ± 2) nucleotides before dissociating. Fitting to an n-step kinetic model suggests that the helicase displays a nonuniform translocation mechanism in which it moves approximately five nucleotides rapidly before undergoing a rate-limiting kinetic slow step. Unexpectedly, RecQ requires a length of 34( ± 3) nucleotides to bind and translocate on ssDNA. This large site size suggests that several monomers are required to bind DNA prior to translocation. Energetically, the RecQ helicase couples the hydrolysis of one ATP molecule to the translocation of more than one nucleotide (1.6 ± 0.3). Thus, our data show that RecQ translocates on ssDNA by efficiently coupling the hydrolysis of one ATP molecule into structural alterations that result in movement of approximately two nucleotides, presumably by an inchworm mechanism. These attributes are consistent with the function of RecQ in recombination and replication.

Abstract P088: The Rate of Inorganic Phosphate Release in Contracting Rat Trabeculae Is Independent of Calcium After Stretch

We aim to reveal the molecular mechanism underlying the force response to stretch in the heart by examining the dependence of the rate of inorganic phosphate (P i ) release in response to stretch on the degree of calcium activation. Permeabilized trabeculae of rat heart are activated by photolytic release of ATP, at 20°C, in the presence of saturating (32µM), or half-saturating (1µM), calcium concentrations, at an initial sarcomere length of 1.9 or 2.1 µm. For trabeculae with an initial sarcomere length of 1.9 µm, the trabeculae are stretched to 2.1 µm during the isometric plateau, held at a constant length and returned to their original length. The rate of P i release is determined by the fluorescence change associated with phosphate binding to a fluorescently-labelled phosphate binding protein diffused into the preparation. At an initial sarcomere length of 1.9µm, the isometric force at full activation was 51 kN.m −2 compared to 26kN.m −2 at half-maximal activation. During the isometric phase, P i release is at a steady rate of 8.2 and 4.8 s −1 (assuming a myosin head concentration of 120µM) at 32 and 1µM calcium, respectively. During stretch, the rate of P i release decreases markedly at both activation levels, to1.0 and 1.4s −1 respectively. Activation from an initial sarcomere length of 2.1µm produced an isometric force of 65.5 kN.m −2 with a steady P i release rate of 8.1 s −1 at maximal activation, and an isometric force of 49.2 kN.m −2 with a steady P i release rate of 4.8 s −1 at half-maximal activation. The rates of P i release during stretch and after the end of the stretch at low activation are equal to that at high activation indicating stretch-induced activation which occurs for stretches applied prior to activation, and during activation. The results demonstrate that stretch has a dramatic effect causing an immediate reduction in the rate of P i release. Stretch contributes to activation of the trabecula's actomyosin ATPase in a calcium-independent manner, although the effect is more marked at low activation levels. Thus a direct effect of stretch on thin filament activation contributes to the Frank-Starling law.

Remediation of Eutrophic Water Body by Zoobenthos

To study the temperature factor affecting nutrient release of Cipangopludina Chinensis, laboratory simulation experiments were carried out, and other traits of Cipangopludina Chinensis, such as the effects of nitrogen cycling, phosphorus cycling, suspended substance in water column. Results showed that temperature had great influence on nutrient release of Cipangopaludina Chinensis. The release rate of total nitrogen and dissolved nitrogen increased, but not clear. The release rate of total phosphorus and dissolved Phosphorus increased greatly. When the temperature rose from 8 °Cto15 °C and 35 °C, the release rate of total nitrogen was increased by 5.71% and 23.43%;The release rate of dissolved nitrogen was increased by 6.76% and 17.57%. While the release rate of total phosphorus was increased by 92.60% and 208.35%,the release rate of dissolved phosphorus was increased by 2.25% and 110.17%. At the same situation, the release rate of ammonia nitrogen was increased by 1.89% and 26.55%, The release rate of phosphate was increased by14.27% and 225.96%, but temperature had little influence on nitrate nitrogen. In addition, temperature had little influence on suspended substance(P&gt;0.05). In a word, zoobenthos play a significant role on eutrophic purification, which provide reference for lake eutrophication control.

Innovative anaerobic/upflow sludge blanket filtration bioreactor for phosphorus removal from wastewater

Phosphorus is the key element to remove from aquatic environments to limit the growth of aquatic plants and algae and, thus, to control eutrophication. Because the upflow sludge blanket filtratio' (USBF) process, without addition of metal salts, entails low efficiency for phosphorus removal, we added an anaerobic reactor to the USBF bioreactor in order to promote the simultaneous removal of phosphorus and nitrogen from wastewater. The results revealed that the anaerobic/USBF bioreactor had a phosphorus removal efficiency up to 86%, with a sludge retention time (SRT) of 10 days, a hydraulic retention time (HRT) of 24 hours and an optimum COD/N/P ratio of 100/5/1. This ratio also improved the compaction quality of the sludge blanket in the USBF clarifier. The average specific phosphate uptake rate in the aerobic zone and the average specific phosphate release rate in the anaerobic reactor were 0.014 mg PO4‐P removed/(g VSS·min) and 0.0525 mg PO4‐P released/(g VSS·min), respectively. Secondary phosphorus release in the USBF clarifier was heightened with increasing HRT. Hence, the optimum total HRT can be selected between 16 and 24 hours based on effluent quality. Effluent phosphorus of about 1 mg/L was provided for wastewater with the COD/N/P ratio of 100/5/1 at the sludge age of 10 days and total HRT of 16 hours. This study illustrated that the anaerobic/USBF bioreactor at the optimum operational conditions can be an effective process for phosphorus removal from municipal wastewater.

A Hearing Loss-Associated myo1c Mutation (R156W) Decreases the Myosin Duty Ratio and Force Sensitivity

myo1c is a member of the myosin superfamily that has been proposed to function as the adaptation motor in vestibular and auditory hair cells. A recent study identified a myo1c point mutation (R156W) in a person with bilateral sensorineural hearing loss. This mutated residue is located at the start of the highly conserved switch 1 region, which is a crucial element for the binding of nucleotide. We characterized the key steps on the ATPase pathway at 37 °C using recombinant wild-type (myo1c(3IQ)) and mutant myo1c (R156W-myo1c(3IQ)) constructs that consist of the motor domain and three IQ motifs. The R156W mutation only moderately affects the rates of ATP binding, ATP-induced actomyosin dissociation, and ADP release. The actin-activated ATPase rate of the mutant is inhibited >4-fold, which is likely due to a decrease in the rate of phosphate release. The rate of actin gliding, as measured by the in vitro motility assay, is unaffected by the mutation at high myosin surface densities, but the rate of actin gliding is substantially reduced at low surface densities of R156W-myo1c(3IQ). We used a frictional loading assay to measure the affect of resisting forces on the rate of actin gliding and found that R156W-myo1c(3IQ) is less force-sensitive than myo1c(3IQ). Taken together, these results indicate that myo1c with the R156W mutation has a lower duty ratio than the wild-type protein and motile properties that are less sensitive to resisting forces.

A Hearing-Loss Associated Myo1c Mutation (r156w) Decreases the Myosin Duty Ratio and Force Sensitivity

Myo1c is a member of the myosin superfamily that has been proposed to function as the adaptation motor in vestibular and auditory hair cells. A recent study identified a myo1c point mutation (R156W) in a person with bilateral sensorineural hearing loss. This mutation is located at the start of the highly conserved switch-1 region, which is a crucial element for the binding of nucleotide. We characterized the key steps on the ATPase pathway at 37oC using recombinant wild-type (myo1c3IQ) and mutant myo1c (R156W-myo1c3IQ) constructs that consist of the motor domain and three IQ motifs. The R156W mutation only moderately affects the rates of ATP binding, ATP-induced actomyosin dissociation, and ADP release. The actin-activated ATPase rate of the mutant is inhibited > 4-fold, which is likely due to a decrease in the rate of phosphate release. The rate of actin gliding, as measured by the in vitro motility assay, is unaffected by the mutation at high myosin surface densities, but actin gliding is substantially reduced at low surface densities of R156W-myo1c3IQ. We used a frictional-loading assay to measure the affect of resisting forces on the rate of actin gliding and found that R156W-myo1c3IQ is less force sensitive than myo1c3IQ. Taken together, these results indicate that myo1c with the R156W mutation has a lower duty ratio than the wild-type protein, and it has motile properties that are less sensitive to resisting forces.

Purification of Actin from Fission Yeast Schizosaccharomyces pombe and Characterization of Functional Differences from Muscle Actin

Fission yeast Schizosaccharomyces pombe is an important genetic model organism for studying the mechanisms of endocytosis and cytokinesis. However, most work on the biochemical properties of fission yeast actin-binding proteins has been done with skeletal muscle actin for matters of convenience. When simulations of mathematical models of the mechanism of endocytosis were compared with events in live cells, some of the reactions appeared to be much faster than observed in biochemical experiments with muscle actin. Here, we used gelsolin affinity chromatography to purify actin from fission yeast. S. pombe actin shares many properties with skeletal muscle actin but has higher intrinsic nucleotide exchange rate, faster trimer nucleus formation, faster phosphate dissociation rate from polymerized actin, and faster nucleation of actin filaments with Arp2/3 complex. These properties close the gap between the biochemistry and predictions made by mathematical models of endocytosis in S. pombe cells.

Experimental evaluation of decrease in the activities of polyphosphate/glycogen‐accumulating organisms due to cell death and activity decay in activated sludge

Decrease in bacterial activity (biomass decay) in activated sludge can result from cell death (reduction in the amount of active bacteria) and activity decay (reduction in the specific activity of active bacteria). The goal of this study was to experimentally differentiate between cell death and activity decay as the cause of decrease in bacterial activity. By means of measuring maximal anaerobic phosphate release rates, verifying membrane integrity by live/dead staining and verifying presence of 16S rRNA with fluorescence in situ hybridization (FISH), the decay rates and death rates of polyphosphate-accumulating organisms (PAOs) in a biological nutrient removal (BNR) system and a laboratory phosphate removing sequencing batch reactor (SBR) system were determined, respectively, under famine conditions. In addition, the decay rate and death rate of glycogen-accumulating organisms (GAOs) in a SBR system with an enrichment culture of GAOs were also measured under famine conditions. Hereto the maximal anaerobic volatile fatty acid uptake rates, live/dead staining, and FISH were used. The experiments revealed that in the BNR and enriched PAO-SBR systems, activity decay contributed 58% and 80% to the decreased activities of PAOs, and that cell death was responsible for 42% and 20% of decreases in their respective activities. In the enriched GAOs system, activity decay constituted a proportion of 74% of the decreased activity of GAOs, and cell death only accounted for 26% of the decrease of their activity.

Phosphorus cycling in marine sediments from the continental margin off Namibia

In this study we investigate benthic phosphorus cycling in recent continental margin sediments at three sites off the Namibian coastal upwelling area. Examination of the sediments reveals that organic and biogenic phosphorus are the major P-containing phases preserved. High C org/P org ratios just at the sediment surface suggest that the preferential regeneration of phosphorus relative to that of organic carbon has either already occurred on the suspension load or that the organic matter deposited at these sites is already rather refractory. Release of phosphate in the course of benthic microbial organic matter degradation cannot be identified as the dominating process within the observed internal benthic phosphorus cycle. Dissolved phosphate and iron in the pore water are closely coupled, showing high concentrations below the oxygenated surface layer of the sediments and low concentrations at the sediment–water interface. The abundant presence of Fe(III)-bound phosphorus in the sediments document the co-precipitation of both constituents as P-containing iron (oxyhydr)oxides. However, highly dissolved phosphate concentrations in pore waters cannot be explained, neither by simple mass balance calculations nor by the application of an established computer model. Under the assumption of steady state conditions, phosphate release rates are too high as to be balanced with a solid phase reservoir. This discrepancy points to an apparent lack of solid phase phosphorus at sediment depth were suboxic conditions prevail. We assume that the known, active, fast and episodic particle mixing by burrowing macrobenthic organisms could repeatedly provide the microbially catalyzed processes of iron reduction with authigenic iron (oxyhydro)oxides from the oxic surface sediments. Accordingly, a multiple internal cycling of phosphate and iron would result before both elements are buried below the iron reduction zone.

019 The time course of inorganic phosphate release and actomyosin ATPase rate in permeabilised cardiac trabeculae

019 The time course of inorganic phosphate release and actomyosin ATPase rate in permeabilised cardiac trabeculae