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1.
The simple Langmuir isotherm is frequently employed to describe the equilibrium behavior of protein adsorption on a wide variety
of adsorbents. The two adjustable parameters of the Langmuir isotherm—the saturation capacity, orq
m, and the dissociation constant,K
d—are usually estimated by fitting the isotherm equation to the equilibrium data acquired from batch equilibration experiments.
In this study, we have evaluated the possibility of estimatingq
m andK
d for the adsorption of bovine serum albumin to a cation exchanger using batch kinetic data. A rate model predicated on the
kinetic form of the Langmuir isotherm, with three adjustable parameters (q
m,K
d, and a rate constant), was fitted to a single kinetic profile. The value ofq
m determined as the result of this approach was quantitatively consistent with theq
m value derived from the traditional batch equilibrium data. However, theK
d value could not be retrieved from the kinetic profile, as the model fit proved insensitive to this parameter. Sensitivity
analysis provided significant insight into the identifiability of the three model parameters. 相似文献
2.
Summary. Patch-clamp whole-cell and single-channel recording techniques were used to investigate the regulation of outward K+ channels by external and internal protons in Brassica chinensis pollen protoplasts. Outward K+ currents and conductance were insensitive to external pH (pHo) except at pH 4.5. Maximal conductance (G
max) for the outward K+ currents was inhibited at acidic external pH. Half-activation voltage (E
1/2) for the outward K+ currents shifted to more positive voltages along with the decrease in pHo. E
1/2 can be described by a modified Henderson–Hasselbalch equation expected from a single titratable binding site. The activation
kinetics of the outward K+ channels was largely insensitive to pHo. An internal pH (pHi) of 4.5 significantly increased outward K+ currents and conductance. G
max for the outward K+ currents decreased with elevations in pHi. In contrast to the effect of pHo, E
1/2 was shifted to more positive voltages with elevations in pHi. The outward K+ currents, G
max and E
1/2 can be described by the modified Henderson–Hasselbalch equation. Furthermore, acidifying pHi accelerated the activation of the outward K+ currents significantly. The differences in electro-physiological properties among previously reported and currently described
plant outward K+ channels may reflect differences in the structure of these channels.
Received May 7, 2002; accepted July 9, 2002; published online November 29, 2002 相似文献
3.
Hans Oberleithner Ulrich Kersting Stefan Silbernagl Wieland Steigner Ulrich Vogel 《The Journal of membrane biology》1989,111(1):49-56
Summary We have chosen the MDCK cell line to investigate aldosterone action on H+ transport and its role in regulating cell membrane K+ conductance (G
m
K
). Cells grown in a monolayer respond to aldosterone indicated by the dose-dependent formation of domes and by the alkalinization of the dome fluid. The pH sensitivity of the plasma membrane K+ channels was tested in giant cells fused from individual MDCK cells. Cytoplasmic pH (pH
i
) andG
m
K
were measured simultaneously while the cell interior was acidified gradually by an extracellular acid load. We found a steep signoidal relationship between pH
i
andG
m
K
(Hill coefficient 4.4±0.4), indicating multiple H+ binding sites at a single K+ channel. Application of aldosterone increased pH
i
within 120 min from 7.22±0.04 to 7.45±0.02 and from 7.15±0.03 to 7.28±0.02 in the absence and presence of the CO2/HCO
3
–
buffer system, respectively. We conclude that the hormone-induced cytoplasmic alkalinization in the presence of CO2/ HCO
3
–
is limited by the increased activity of a pH
i
-regulating HCO
3
–
extrusion system. SinceG
m
K
is stimulated half-maximally at the pH
i
of 7.18±0.04, internal H+ ions could serve as an effective intracellular signal for the regulation of transepithelial K+ flux. 相似文献
4.
G. P. Findlay 《The Journal of membrane biology》1982,68(1):179-189
Summary In cells of the freshwater algaHydrodictyon africanum, in solutions where [K+]0=0.1mm and pH0>7.0, the membrane in the light is hyperpolarized. The membrane potential difference {ie179-1} has values from –180 to –275 mV, more negative than any ion diffusion potential difference, and is predominantly a function of pH0, and independent of [K+]0. The hyperpolarization of the membrane appears to arise from an electrogenic efflux of H+, estimated from voltage-clamp data to be about 8 nmol m–2 sec–1 when pH0=8.5. In the light the membrane conductanceg
m is about 0.084 S m–2. At light-off, {ie179-2} becomes less negative, with a halftime for change of 15 to 30 sec andg
m decreases by about 0.052 S m–2. After dark periods of up to 300 sec, {ie179-3} is largely independent of pH0 for values greater than 6.0 and usually behaves as a combined K+ and Na+ diffusion potential with permeability ratioP
Na/P
K=0.05 to 0.2. The membrane potassium conductanceg
K has either a low value of 2–6×10–2 Sm–2, or a high value of up to 18×10–2 S m–2 depending on [K+]0, the transition from low to high values occurring when {ie179-4} moves over a threshold value that is more negative than {ie179-5}, the electrochemical equilibrium potential for K+. The time for half-change of the transition is about 30 sec. The results are consistent with a model of the membrane in which the pump electromotive force and conductance are in parallel with diffusive electromotive forces and conductances. When the pump is operating its properties determine membrane properties, and when it is inoperative, or running at a diminished rate, the membrane properties are determined more by the diffusive pathways. Changes in both pump rate andg
K can account for a variety of characteristic changes in membrane PD and conductance occurring in response to ligh-dark changes, changes in light intensity, pasage of externally applied electric current across the membrane and changes in ionic constituents of the external medium. 相似文献
5.
《Chemical Speciation and Bioavailability》2013,25(2):29-36
AbstractThe noncovalent interactions of phytate (Phy6-) with biogenic amines were studied potentiometrically in aqueous solution, at t= 25°C. Several species are formed in the different H+-Phy6--amine (A) systems, which have the general formula Ap(Phy)Hq(12-q)-, with p ≤ 3 and 6 ≤ q ≤ 10. The stability of these species is strictly dependent on the charges involved in the formation equilibria. For the equilibrium pHiAi+ + Hj(Phy)(12-j)- = Ap(Phy)Hq(12q)-, (q = pi + j)we found the relationship logK= aζ (ζ is the charge product of reactants), where a= 0.35(0.03, valid for all the amines; this roughly indicates an average free energy contribution per bond -ΔG0 = 4.0 ± 0.2 kJ mol-1. A slightly more sophisticated equation is also proposed for predicting the stability of these species. Owing to the quite high (partially protonated) phytate charge, the stability of Ap(Phy)Hq(12-q)- species is quite high, making phytate a strong amine sequestering agent in a wide pH range. 相似文献
6.
Mortimer M. Civan Stephen R. Williams David G. Gadian Enrique Rozengurt 《The Journal of membrane biology》1986,94(1):55-64
Summary Swiss mouse 3T3 cells grown on microcarrier beads were superfused with electrolyte solution during continuous NMR analysis. Conventional31P and19F probes of intracellular pH (pH
c
) were found to be impracticable. Cells were therefore superfused with 1 to 4mm 2-deoxyglucose, producing a large intracellular, pH-sensitive signal of 2-deoxyglucose phosphate (2DGP). The intracellular incorporation of 2DGP inhibited the Embden-Meyerhof pathway. However, intracellular ATP was at least in part retained and the cellular responsivity to changes in extracellular ionic composition and to the application of growth factors proved intact. Transient replacement of external Na+ with choline or K+ reversibly acidified the intracellular fluids. Quiescent cells and mitogenically stimulated cells displayed the same dependence of shifts in pH
c
on external Na+ concentration (c
Na
o
). pH
c
also depended on intracellular Na+ concentration (c
Na
o
). Increasingc
Na
c
by withdrawing external K+ (thereby inhibiting the Na,K-pump) caused reversible intracellular acidification; subsequently reducingc
Na
o
produced a larger acid shift in pH
c
than with external K+ present. Comparison of separate preparations indicated that pH
c
was higher in stimulated than in quiescent cells. Transient administration of mitogens also reversibly alkalinized quiescent cells studied continuously. This study documents the feasibility of monitoring pH
c
of Swiss mouse 3T3 cells using31P NMR analysis of 2DGP. The results support the concept of a Na/H antiport operative in these cells, both in quiescence and after mitogenic stimulation. The data document by an independent technique that cytoplasmic alkalinization is an early event in mitogenesis, and that full activity of the Embden-Meyerhof pathway is not required for the expression of this event. 相似文献
7.
S. Y. Chow Y. C. Yen-Chow H. S. White L. Hertz D. M. Woodbury 《Neurochemical research》1991,16(12):1275-1283
Inastrocytes, as [K+]o was increased from 1.2 to 10 mM, [K+]i and [Cl–]i were increased, whereas [Na+]i was decreased. As [K+]o was increased from 10 to 60 mM, intracellular concentration of these three ions showed no significant change. When [K+]o was increased from 60 to 122 mM, an increase in [K+]i and [Cl–]i and a decrease in [Na+]i were observed.Inneurons, as [K+]o was increased from 1.2 to 2.8 mM, [Na+]i and [Cl–]i were decreased, whereas [K+]i was increased. As [K+]o was increased from 2.8 to 30 mM, [K+]i, [Na+]i and [Cl–]i showed no significant change. When [K+]o was increased from 30 to 122 mM, [K+]i and [Cl–]i were increased, whereas [Na+]i was decreased. Inastrocytes, pHi increased when [K+]o was increased. Inneurons, there was a biphasic change in pHi. In lower [K+]o (1.2–2.8 mM) pHi decreased as [K+]o increased, whereas in higher [K+]o (2.8–122 mM) pHi was directly related to [K+]o. In bothastrocytes andneurons, changes in [K+]o did not affect the extracellular water content, whereas the intracellular water content increased as the [K+]o increased. Transmembrane potential (Em) as measured with Tl-204 was inversely related to [K+]o between 1.2 and 90 mM, a ten-fold increase in [K+]o depolarized the astrocytes by about 56 mV and the neurons about 52 mV. The Em values measured with Tl-204 were close to the potassium equilibrium potential (Ek) except those in neurons at lower [K+]o. However, they were not equal to the chloride equilibrium potential (ECl) at [K+]o lower than 30 mM in both astrocytes and neurons. Results of this study demonstrate that alteration of [K+]o produced different changes in [K+]i, [Na+]i, [Cl–]i, and pHi in astrocytes and neurons. The data show that astrocytes can adapt to alterations in [K+]o, in such a way to maintain a more suitable environment for neurons. 相似文献
8.
Summary The intracellular pH (pH
i
) of Ehrlich ascites tumor cells, both in the steady state and under conditions of acid loading or recovery from acid loading, was investigated by measuring the transmembrane flux of H+ equivalents and correlating this with changes in the distribution ratio of dimethyloxazolidine-2,4-dione (DMO). The pH
i
of cells placed in an acidic medium (pH
o
below 7.15) decreases and reaches a steady-state value that is more alkaline than the outside. For example when pH
o
is acutely reduced to 5.5, pH
i
falls exponentially from 7.20 ± 0.06 to 6.29 ± 0.04 with a halftime of 5.92 ± 1.37 min, suggesting a rapid influx of H+. The unidirectional influx of H+ exhibits saturation kinetics with respect to extracellular [H+]; the maximal flux is 15.8 ± 0.05 mmol/(kg dry wt · min) andK
m
is 0.74 ± 0.09 × 10–6
m.Steady-state cells with pH
i
above 6.8 continuously extrude H+ by a process that is not dependent on ATP but is inhibited by anaerobiosis. Acid-loaded cells (pH
i
6.3) when returned to pH
o
7.3 medium respond by transporting H+, resulting in a rapid rise in pH
i
. The halftime for this process is 1.09 ± 0.22 min. The H+ efflux measured under similar conditions increases as the intracellular acid load increases. An ATP-independent as well as an ATP-dependent efflux contributes to the restoration of pH
i
to its steady-state value. 相似文献
9.
The activity of the Escherichia coli K+ transport system TrkA was measured as a function of the cytoplasmic pH of the cell. For this purpose, pHin was decreased by the addition of the weak acids acetic acid, benzoic acid or salicylic acid to K+-depleted cells. Under these conditions, the initial rate of K+ uptake decreased strongly with pHin, and was almost independent of the acid used. This inhibition was due to a strong decrease in the Vmax for K+ uptake, which indicates that low cytoplasmic pH inactivates the TrkA K+ uptake system. The relevance of this inhibition for growth and metabolism at low pHin is discussed. 相似文献
10.
Wenhui Wang Robert M. Henderson John Geibel Stanley White Gerhard Giebisch 《The Journal of membrane biology》1989,112(3):277-289
Summary Isolated early distal tubule cells (EDC) of frog kidney were incubated for 20–28 hr in the presence of aldosterone and then whole-cell K+ currents were measured at constant intracellular pH by the whole-cell voltage-clamp technique. Aldosterone increased barium-inhibitable whole-cell K+ conductance (gK+) threefold. This effect was reduced by amiloride and totally abolished by ouabain. However, aldosterone could still raisegK+ in ouabain-treated cells in the presence of furosemide.We tested whether changes in intracellular pH (pH
i
) could be a signal for cells to regulategK+. After removal of aldosterone, the increase ingK+ was preserved by subsequent incubation for 8 hr at pH 7.6 but abolished at pH 6.6. In the complete absence of aldosterone, incubation of cells at pH 8.0 for 20–28 hr raised pH
i
and doubledgK+.Using the patch-clamp technique, three types of K+-selective channels were identified, which had conductances of 24, 45 and 59 pS.Aldosterone had no effect on the conductance or open probability (P
o) of any of the three types of channels. However, the incidence of observing type II channels was increased from 4 to 22%. Type II channels were also found to be pH sensitive,P
o was increased by raising pH.These results indicate that prolonged aldosterone treatment raises pH
i
and increasesgK+ by promoting insertion of K+ channels into the cell membrane. Channel insertion is itself triggered by raising both pH
i
and increasing the activity of the Na+/K+ pump in early distal cells of frog kidney.
Present address: Department of Physiology, The University of Leeds, Leeds, LS2 9NQ, England 相似文献
11.
A differential elimination method (DEM) is developed to determine the kinetic coefficients for substrate self-inhibition.
Finite differentiation of the equation eliminates either KI or KS, which enables the equation to be linearized so that
[^(\textq)] {\hat{\text{q}}} , KS, and KI can be estimated without using nonlinear least square regression (NLSR). The DEM options that eliminate KI or KS computed the parameter values exactly when the data did not contain any errors. If one-point or random errors were not too
large, both DEM options worked as well as NLSR when data were acquired with geometric intervals for substrate concentration.
The DEM was more accurate for fitting the data for the smallest and largest values of S, but relatively weaker in estimating
the observed maximum substrate utilization rate, qmax. The estimates for Smax, the concentration at which the maximum specific substrate utilization rate is observed, were relatively invariant among
the methods, even when KS and KI differed. When the intervals were arithmetic (i.e., equal intervals of substrate concentration) and the data contained errors,
the DEM and NLSR estimated the parameters poorly, indicating that collecting data with an arithmetic interval greatly increases
the risk of poor parameter estimation. Parameter estimates by DEM fit very well experimental data from nitrification or photosynthesis,
which were taken with geometric intervals of substrate concentration or light intensity, but fit poorly phenol-degradation
data, which were obtained with arithmetic substrate intervals. Besides providing a reasonable substitute for NLSR, the DEM
also can be used as a tool to diagnose the quality of experimental data by comparing its estimates between the DEM options,
or, more rigorously, to those from NLSR. 相似文献
12.
Summary Recently we proposed that cytoplasmic acidification of low K+ (LK) sheep erythrocytes may stimulate ouabain-resistant Cl–-dependent K+ flux (K+Cl– cotransport), also known to be activated by cell swelling, treatment with N-ethylmaleimide (NEM), or removal of cellular bivalent cations. Here we studied the dependence of K+ transport on intracellular and extracellular pH (pH
i
, pH
o
) varied either simultaneously or independently using the Cl–/HCO
3
–
exchange inhibitor 4,4, diisothiocyanatostilbene-3,2-disulfonic acid (DIDS). In both control and NEM-treated LK cells volumes were kept near normal by varying extracellular sucrose. Using DIDS as an effective pH clamp, both K+ efflux and influx of Rb+ used as K+ congener were strongly activated at acid pH
i
and alkaline pH
o
. A small stimulation of K+ (Rb+) flux was also seen at acid pH
i
in the absence of DIDS, i.e., when pH
i
pH
o
. Anti-L
l
serum, known to inhibit K+Cl– cotransport, prevented the pH
i
-stimulated K+ (Rb+) fluxes. Subsequent to NEM treatment at pH 6, K+ (Rb+) fluxes were activated only by raising pH, and thus were similar to the pH activation profile of K+ (Rb+) fluxes in DIDS-treated cells with pH
o
varied at constant physiologic pH
i
. Anti-L
l
, which inhibited NEM-stimulated K+ (Rb+) fluxes, failed to do so in NEM-plus DIDS-treated cells. Thus, NEM treatment interferes with the internal but not with the external pH-sensitive site. 相似文献
13.
ABA stimulation of outward K+ current (I
K,out) in Vicia faba guard cells has been correlated with a rise in cytosolic pH (pH
i
). However, the underlying mechanism by which I
K,out is affected by pH
i
has remained unknown. Here, we demonstrate that pH
i
regulates outward K+ current in isolated membrane patches from Vicia faba guard cells. The stimulatory effect of alkalinizing pH
i
was voltage insensitive and independent of the two free calcium levels tested, 50 nm and 1 μm. The single-channel conductance was only slightly affected by pH
i
. Based on single-channel measurements, the kinetics of time-activated whole-cell current, and the analysis of current noise
in whole-cell recordings, we conclude that alkaline pH
i
enhances the magnitude of I
K,out by increasing the number of channels available for activation. The fact that the pH
i
effect is seen in excised patches indicates that signal transduction pathways involved in the regulation of I
K,out by pH
i
, and by implication, components of hormonal signal transduction pathways that are downstream of pH
i
, are membrane-delimited.
Received: 5 June 1996/Revised: 1 August 1996 相似文献
14.
The activation by abscisic acid (ABA) of current through outward-rectifying K+ channels and its dependence on cytoplasmic pH (pHi) was examined in stomatal guard cells of Vicia faba L. Intact guard cells were impaled with multibarrelled and H+-selective microelectrodes to record membrane potentials and pHi during exposures to ABA and the weak acid butyrate. Potassium channel currents were monitored under voltage clamp and, in some experiments, guard cells were loaded with pH buffers by iontophoresis to suppress changes in pHi. Following impalements, stable pHi values ranged between 7.53 and 7.81 (7.67±0.04, n = 17). On adding 20 M ABA, pHi rose over periods of 5–8 min to values 0.27±0.03 pH units above the pHi before ABA addition, and declined slowly thereafter. Concurrent voltage-clamp measurements showed a parallel rise in the outward-rectifying K+ channel current (IK, out) and, once evoked, both pHi and IK, out responses were unaffected by ABA washout. Acid loads, imposed with external butyrate, abolished the ABA-evoked rise in IK, out. Butyrate concentrations of 10 and 30 mM (pH0 6.1) caused pHi to fall to values near 7.0 and below, both before and after adding ABA, consistent with a cytoplasmic buffer capacity of 128±12 mM per pH unit (n = 10) near neutrality. Butyrate washout was characterised by an appreciable alkaline overshoot in pHi and concomitant swell in the steady-state conductance of IK, out. The rise in pHi and iK, out in ABA were also virtually eliminated when guard cells were first loaded with pH buffers to raise the cytoplasmic buffer capacity four- to sixfold; however, buffer loading was without appreciable effect on the ABA-evoked inactivation of a second, inward-rectifying class of K+ channels (IK, in). The pHi dependence of IK, out was consistent with a cooperative binding of at least 2H+ (apparent pKa = 8.3) to achieve a voltage-independent block of the channel. These results establish a causal link previously implicated between cytoplasmic alkalinisation and the activation of IK, out in ABA and, thus, affirm a role for H+ in signalling and transport control in plants distinct from its function as a substrate in H+-coupled transport. Additional evidence implicates a coordinate control of IK, in by cytoplasmic-free [Ca2+] and pHi.Abbreviations ABA
abscisic acid
- [Ca2+]i
cytoplasmic free [Ca2+]i
- EK
K+ equilibrium potential
- IK, out, IK, in
outward-, inward-rectifying K+ channel (current)
- I-V
current-voltage (relation)
- Mes
2-(N-morpholino)ethanesulfonic acid
- pHi
cytoplasmic pH
- Tes
2-{[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]-amino}ethanesulfonic acid
- Vm
membrane potential
We are grateful to G. Thiel (Pflanzenphysiologisches Institut, Universität Göttingen, Germany) for helpful discussions. This work was possible with equipment grants-in-aid from the Gatsby Charitable Foundation, the Royal Society and the University of London Central Research Fund. F.A. holds a Sainsbury Studentship. 相似文献
15.
Harold M. Farrell Jr. Thomas F. Kumosinski 《Journal of industrial microbiology & biotechnology》1988,3(2):61-71
Summary Molecular biology holds the promise of new tools for the food industry which include proteins with tailor-made functionality. Without a fundamental knowledge of the molecular bases of these properties, implementation will be strictly empirical. For example, the phenomena of salt-induced precipitation of proteins (salting-out) and their resolubilization (salting-in) has heretofore been discussed only qualitatively. A quantitative method, using Wyman's theory of thermodynamic linkage, has been developed and tested on the calcium-induced solubility profiles of the major milk proteins, the caseins. Salting-out was described by a salt-binding constant,k
1, andn, the number of moles of salt bound; salting-in was described by the corresponding termsk
2 andm. The magnitude of these parameters indicated involvement of protein phosphate groups in binding and precipitation, but enzymatic dephosphorylation showed significant increases ink
1 andk
2 indicating involvement of carboxylate groups as well. Studies on two genetic variants of s1-casein indicated the importance of a hydrophobically stabilized intramolecular ion pair in the functionality of the protein. These studies have led to a fuller understanding of the molecular basis for the solubility behavior of caseins and have laid the groundwork for future computer simulation of food protein functionality. 相似文献
16.
S. Gaillard J. L. Rodeau 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1987,157(4):435-444
Summary Intracellular pH (pHi) regulation was studied in crayfish neurons with pH-, and Na+-sensitive microelectrodes. It was confirmed to involve both a HCO
3
–
-dependent and a HCO
3
–
-independent mechanism. The latter was identified as the amiloride-sensitive Na+/H+ exchange described in vertebrate cells. Its dependence on extracellular pH (pHe) and Na+ concentration ([Na+]e) was studied in CO2-free external solutions at 20°C. The steady state pHi and the rate constant (k) of the exponential pHi recovery following an acid load were determined. At pHe=7.5 and [Na+]e=200 mM, the average steady state pHi was 7.09±0.12 (as compared to 7.30±0.10 in the presence of 5 mM bicarbonate). The dependence of the rate constant of recovery on [Na+]e could be described by Michaelis-Menten kinetics; at pHe=7.5 the apparentK
m andK
max were 39 mM and 1.4 mmol·l–1·min–1, respectively. Decreasing pHe reduced the rate of recovery, the variations ofk with pHe conforming to a simple titration curve with an apparent pK of 7.05±0.21. These kinetic properties of the Na+/H+ exchange in crayfish neurons are similar to those described in vertebrate cells.Preliminary results were presented at the First International Congress of Comparative Physiology and Biochemistry (Liège, Belgium, 1984) 相似文献
17.
18.
Summary Membrane-permeant weak acids and bases, when applied to the bath, modulate the resting membrane potential and the glucose-induced electrical activity of pancreatic B cells, as well as their insulin secretion. These substances alter the activity of a metabolite-regulated. ATP-sensitive K+ channel which underlies the B-cell resting potential. We now present several lines of evidence indicating that the channel may be directly gated by pH
i
. (1) The time course of K+(ATP) channel activity during exposure to and washout of NH4Cl under a variety of experimental conditions, including alteration of the electrochemical gradient for NH4Cl entry and inhibition of the Na
o
+
H
i
+
exchanger, resembles the time course of pH
i
measured in other cell types that have been similarly treated. (2) Increasing pH
o
over the range 6.25–7.9 increases K+(ATP) channel activity in cell-attached patches where the cell surface exposed to the bath has been permeabilized to H+ by the application of the K+/H+ exchanger nigericin. (3) Increasing pH
i
over a similar range produces similar effects on K+(ATP) channels in inside-out excised patches exposed to small concentrations of ATP
i
. The physiological role of pH
i
in the metabolic gating of this channel remains to be explored. 相似文献
19.
M. Boon T. A. Meeder C. Thöne C. Ras J. J. Heijnen 《Applied microbiology and biotechnology》1999,51(6):820-826
The oxidation and growth kinetics of ferrous iron with Thiobacillus ferrooxidans in continuous cultures was examined at several total iron concentrations. On-line off-gas analyses of O2 and CO2 were used to measure the oxygen and carbon dioxide consumption rates in the culture. Off-line respiration measurements in
a biological oxygen monitor (BOM) were used to measure directly the maximum specific oxygen consumption rate, qO2,max, of cells grown in continuous culture. It was shown that these reproducibly measured values of qO2,max vary with the dilution rate. The biomass-specific oxygen consumption rate, qO2, is dependent on the ratio of the ferric and ferrous iron concentrations in the culture. The oxidation kinetics was accurately
described with a rate equation for competitive ferric iron inhibition, using the value of qO2,max measured in the BOM. Accordingly, only the kinetic constant Ks/K
i needed to be fitted from the measurements. A new method was introduced to determine the steady-state kinetics of a cell suspension
in a batch culture that only takes a few hours. The batch culture was set up by terminating the feeding of a continuous culture
at its steady state. The kinetic constant K
s/K
i determined in this batch culture agreed with the value determined in continuous cultures at various steady states.
Received: 8 February 1999 / Accepted: 17 February 1999 相似文献
20.
Two chemicals,A andB, are allowed to diffuse together and a reaction described by $$A + B\mathop \rightleftharpoons \limits_{K_{ - 1} }^{K_1 } C$$ is allowed to proceed. This system is described mathematically by a system of partial differential equations. A numerical procedure is presented to find the rate constants ofK 1 andK ?1. A systematic analysis of the effects of errors is also presented. 相似文献