Estimating Michaelis–Menten Parameters and Lake Water Phosphate by the Rigler Bioassay: Importance of Fitting Technique, Plankton Size, and Substrate Range

1991 ◽  
Vol 48 (1) ◽  
pp. 73-83 ◽  
Author(s):  
E. Bentzen ◽  
W. D. Taylor
Keyword(s):  
Nonlinear Model ◽  
Lake Water ◽  
Upper Bound ◽  
Uptake Rate ◽  
Size Fraction ◽  
Simulated Data ◽  
Kinetic Experiment ◽  
Ambient Concentration ◽  
Uptake Rate Constant ◽  
Mixed Community

Evaluation of the Michaelis–Menten parameters Vm and Kt for phosphate (PO43−) uptake by plankton is difficult because of differences in nutrient uptake by the various species. Studies using simulated data have shown that fitting the equation by nonlinear regression is preferable to linearized transformations for estimating Vm and Kt; however, the actual velocity of PO43− uptake by lake plankton cannot be measured because the ambient concentration of PO43− (Pn) is unknown. For natural plankton, a better fit is demonstrated using another nonlinear model which fits the uptake rate constant for 32PO43− directly to the PO43− added in the kinetic experiment, and the mixed community effect is minimized by isolating different plankton size fractions. Another consequence of not knowing Pn is that the estimate of Kt cannot be distinguished from Pn′ and the sum of the two is always obtained. The low substrate region of the Michaelis–Menten curve is used in the Rigler bioassay as a means of estimating the upper bound to Pn. Error in the uptake rate constants influences the estimate of the Rigler Pn′ and the Rigler maximum Pn is equal to the estimated (Kt + Pn) of the 0.2–1 μm size fraction.

Chemical and Radiotracer Measurements of Phosphorus Uptake by Lake Plankton

1983 ◽  
Vol 40 (2) ◽  
pp. 147-155 ◽  
Author(s):  
D. R. S. Lean ◽  
E. White
Keyword(s):  
Rate Constant ◽  
Lake Water ◽  
Uptake Rate ◽  
Phosphorus Uptake ◽  
Small Cells ◽  
Phosphate Limitation ◽  
Isotope Method ◽  
Uptake Rate Constant ◽  
Ambient Concentrations ◽  
Uptake Velocity

Either chemical or radioisotope methods can be used to measure the maximum uptake velocity for phosphorus in lake water but neither can measure uptake at ambient concentrations. Chemical estimates at ambient concentrations are insensitive and the isotope method provides the uptake rate constant only. By multiplying the uptake rate constant by the ambient phosphate concentration one obtains an estimate for phosphorus influx, but reliable estimates for ambient phosphate concentrations are still unattainable. At added phosphate levels even up to 10 μg P∙L−1, the isotope method overestimates net phosphate uptake because of release of phosphate from the plankton. Influx and efflux are practically equal under steady state conditions, and during periods of phosphate limitation a net uptake of phosphorus occurs only when there is an increase in the phosphorus supply. The uptake of phosphate is predominantly by small cells at low concentrations of added phosphate and by larger cells at the higher enrichments. This makes the use of the radiobioassay for estimating ambient phosphate concentrations difficult to interpret. Furthermore the half-saturation coefficients measured for whole lake water are a mean for the entire population and consist of small values for small algae and bacteria and larger values for larger algae.Key words: phosphorus, kinetics, plankton, algae, bacteria nutrition

On the Expansion of Nonlinear Models Using Bell-Shaped Basis Functions

2003 ◽  
Author(s):  
Kiriakos Kiriakidis
Keyword(s):  
Nonlinear Dynamics ◽  
Nonlinear Model ◽  
Upper Bound ◽  
Nonlinear Models ◽  
Approximation Error ◽  
Basis Functions ◽  
Model Set

We propose a method that approximates any nonlinear model, without regard to complexity, by minimizing its distance from a rich model set. The method produces, potentially through an automated procedure, the approximation of the nonlinear dynamics in the form of a finite expansion associated with certain basis functions and provides an upper bound on the approximation error.

scholarly journals Effect of Dopamine Loss and the Metabolite 3-O-Methyl-[18F]Fluoro-dopa on the Relation between the 18F-Fluorodopa Tissue Input Uptake Rate Constant Kocc and the [18F]Fluorodopa Plasma Input Uptake Rate Constant Ki

2003 ◽  
Vol 23 (3) ◽  
pp. 301-309 ◽  
Author(s):  
V. Sossi ◽  
J. E. Holden ◽  
R. de la Fuente-Fernandez ◽  
T. J. Ruth ◽  
A. J. Stoessl
Keyword(s):  
Rate Constant ◽  
Uptake Rate ◽  
Dopaminergic Neurons ◽  
Storage Capacity ◽  
Synthesis Rate ◽  
Positron Emission ◽  
Uptake Rate Constant ◽  
Downward Bias ◽  
Storage Rate ◽  
And Storage

Parkinson disease is characterized by the loss of dopaminergic neurons, thus decreasing the system's ability to produce and store dopamine (DA). Such ability is often investigated using 18F-fluorodopa (FD) positron emission tomography. A commonly used model to investigate the DA synthesis and storage rate is the modified Patlak graphical approach. This approach allows for both plasma and tissue input functions, yielding the respective uptake rate constants Ki and Kocc. This method requires the presence of an irreversible compartment and the absence of any nontrapped tracer metabolite. In the case of Kocc, this last assumption is violated by the presence of the FD metabolite 3- O-methyl-[18F]fluoro-dopa (3OMFD), which makes the Kocc evaluation susceptible to a downward bias. It was found that both Ki and Kocc are influenced by DA loss and thus are not pure measures of DA synthesis and storage. In the case of Kocc, the presence of 3OMFD exacerbates the effect of DA egress, thus introducing a disease-dependent bias in the Kocc determination. These findings imply that Ki and Kocc provide different assessments of disease severity and that, as disease progresses, Ki and especially Kocc become more related to DA storage capacity and less to the DA synthesis rate.

Orthophosphate Uptake Rate Constants are Mediated by the 103–104 Molecular Weight Fraction in Shield Lake Waters

1984 ◽  
Vol 41 (1) ◽  
pp. 166-173 ◽  
Author(s):  
P. Brassard ◽  
J. C. Auclair
Keyword(s):  
Molecular Weight ◽  
Rate Constant ◽  
Uptake Rate ◽  
External Solution ◽  
Phosphorus Compounds ◽  
Phytoplankton Assemblages ◽  
Physiological Basis ◽  
Colloidal Phosphorus ◽  
Uptake Rate Constant ◽  
Lake Waters

Although midsummer chlorophyll concentrations can be predicted from total phosphorus, attempts to identify all bioavailable phosphorus compounds has proven difficult. Inconsistencies in determining colloidal phosphorus utilization and the discovery that orthophosphate concentration and flux are poor predictors of lake trophic status has led us to postulate that other forms of phosphorus compounds, which may not be necessarily labeled over the radioisotopic uptake assay (32P) period, are assimilated by natural phytoplankton assemblages. Using ultrafiltration methodology we test the hypothesis that the orthophosphate uptake rate constant can be physiologically varied upon changing the external concentration of selected molecular weight fractions in Shield lake waters. We determined that the fraction between molecular weight 103 and 104 significantly increased the orthophosphate uptake rate constant when exposed to the natural seston. Our discovery suggests that the orthophosphate uptake rate constant is subject to fluctuations depending on the availability of low molecular weight phosphorus metabolites in the external solution. The physiological basis of our observations may be a metabolic coupling between the activity of plasmalemma-bound phosphatases and the transport of PO43− across the cell membrane.

scholarly journals Limited effects of increased CO2 and temperature on metal and radionuclide bioaccumulation in a sessile invertebrate, the oyster Crassostrea gigas

2015 ◽  
Vol 73 (3) ◽  
pp. 753-763 ◽  
Author(s):  
Murat Belivermiş ◽  
Michel Warnau ◽  
Marc Metian ◽  
François Oberhänsli ◽  
Jean-Louis Teyssié ◽  
...  
Keyword(s):  
Crassostrea Gigas ◽  
Uptake Rate ◽  
Soft Tissues ◽  
Interactive Effect ◽  
Seawater Ph ◽  
The Pacific ◽  
Effects Of Ph ◽  
Uptake Rate Constant ◽  
In Vitro Simulation

Abstract This study investigated the combined effects of reduced pH and increased temperature on the capacities of the Pacific cupped oyster Crassostrea gigas to bioconcentrate radionuclide and metals. Oysters were exposed to dissolved radiotracers (110mAg, 241Am, 109Cd, 57Co, 54Mn, and 65Zn) at three pH (7.5, 7.8, 8.1) and two temperatures (21 and 24°C) under controlled laboratory conditions. Although calcifying organisms are recognized as particularly vulnerable to ocean acidification, the oyster did not accumulate differently the studied metals when exposed under the different pH conditions. However, temperature alone or in combination with pH somewhat altered the bioaccumulation of the studied elements. At pH 7.5, Cd was accumulated with an uptake rate constant twofold higher at 24°C than 21°C. Bioaccumulation of Mn was significantly affected by an interactive effect between seawater pH and temperature, with a decreased uptake rate at pH 7.5 when temperature increased (27 ± 1 vs. 17 ± 1 d−1 at 21 and 24°C, respectively). Retention of Co and Mn tended also to decrease at the same pH with decreasing temperature. Neither pH nor temperature affected strongly the elements distribution between shell and soft tissues. Significant effects of pH were found on the bioaccessibility of Mn, Zn, and 241Am during experimental in vitro simulation of human digestion.

Uptake of monohydric alcohols by liver: demonstration of a shared enzymic space

1983 ◽  
Vol 244 (2) ◽  
pp. G198-G214
Author(s):  
C. A. Goresky ◽  
E. R. Gordon ◽  
G. G. Bach
Keyword(s):  
Rate Constant ◽  
Uptake Rate ◽  
Removal Rate ◽  
Hepatic Uptake ◽  
Multiple Indicator Dilution ◽  
Ethanol Infusion ◽  
Monohydric Alcohols ◽  
Uptake Rate Constant ◽  
Anesthetized Dogs ◽  
Steady State Levels

Multiple-indicator dilution studies of the hepatic uptake of straight-chain C1-C5 monohydric alcohols were carried out in anesthetized dogs, with either no preceding or saturating infusions of ethanol, and at different steady-state levels for the C2 experiments. Labeled red cells were utilized as a vascular reference, and labeled water was used as a second reference entering liver cells. Kinetic analysis of the data provided estimates of both an uptake rate constant and the space of distribution available to label. From the decrease in the uptake rate constant for labeled ethanol with bulk concentration, we calculated a maximal removal rate of 0.025 mumol X s-1 X (ml liver water)-1 and a Michaelis constant (Km) of 0.32 mM. Especially for the labeled C3-C5 alcohols, a space in excess of that available to water was found, and the bulk of this was dissipated by ethanol infusion. The increment, the "shared enzymic space", which varies with enzymic concentration and inversely with Km, was used to calculate Km values for the other alcohols.

Using Market-Level Data to Understand Promotion Effects in a Nonlinear Model

1997 ◽  
Vol 34 (3) ◽  
pp. 322-334 ◽  
Author(s):  
Markus Christen ◽  
Sachin Gupta ◽  
John C. Porter ◽  
Richard Staelin ◽  
Dick R. Wittink
Keyword(s):  
Nonlinear Model ◽  
Simulated Data ◽  
Parameter Estimates ◽  
Econometric Modeling ◽  
Scanner Data ◽  
Aggregation Method ◽  
Marketing Manager ◽  
New Approach ◽  
Level Data

The authors show analytically, empirically, and numerically through simulation that the estimated effects from linearly aggregated market-level data differ substantially from comparable effects that are obtained from store-level data. The magnitude of this difference renders market-level data largely unsuitable for econometric modeling, unless the marketing manager compensates for the bias that results from the incompatible aggregation. The authors introduce a new approach, a relatively simple debiasing procedure derived from simulated data. They show that this debiasing approach results in substantially improved parameter estimates. They illustrate the value of the procedure by applying it to scanner data for powdered detergents and comparing the debiased parameter estimates to results obtained from store-level data and an alternative aggregation method that maintains homogeneity for selected promotional activities.

Uptake from Seawater and Clearance of p,p′-DDT by Marine Planktonic Crustacea

1979 ◽  
Vol 36 (3) ◽  
pp. 247-254 ◽  
Author(s):  
Gareth C. H. Harding ◽  
W. Peter Vass
Keyword(s):  
Surface Area ◽  
Rate Constant ◽  
Uptake Rate ◽  
Rate Constants ◽  
Clearance Rate ◽  
Dry Weight ◽  
Exponential Model ◽  
Uptake Rate Constant ◽  
Clearance Rate Constant ◽  
Planktonic Crustaceans

A simple exponential model is used to interpret the simultaneous uptake and clearance of p,p′-DDT by euphausiids and copepods to and from seawater,[Formula: see text]where [C] and [W] are the concentrations in the organism and seawater, respectively. The clearance rate constant for euphausiids, kj = 0.043/d, is not significantly different from that observed for copepods, 0.048/d. No trend in ki values is detected over the range of p,p′-DDT concentrations in seawater used, 27.8–1388 ng/L. Furthermore, there is a great deal of overlap in the uptake rate constant values between organisms. Uptake rate constants range from 0.76 to 1.21 × 104/d for euphausiids and from 1.04 to 2.51 × 104/d for copepods. There appears to be no need to use a surface-area term if the concentration of p,p′-DDT in the organism is expressed per unit dry weight even though the euphausiids are 2 orders of magnitude larger than copepods. Knowing levels of ΣDDT present in planktonic crustaceans in nature, back calculations suggest that there must be [Formula: see text] ΣDDT/L in seawater. A considerable amount of the ΣDDT reported in seawater must therefore be unavailable to plankters because it is "bound" to particles. Key words: p,p′-DDT, uptake, clearance, surface area, euphausiids, copepods

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