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1.
Abstract: A previous study of the metabolism of 6-[18F]-fluoro-l -3,4-dihydroxyphenylalanine (FDOPA) in rats pretreated with carbidopa contained information amenable to kinetic analysis. Using these data, tracer transfer coefficients and metabolic rate constants were estimated. After intravenous injection, FDOPA in circulation was O-methylated (kD0 = 0.055 min?1), and the metabolite (O-methyl-FDOPA) escaped from plasma with a rate constant (kM?1) of 0.01 min?1. The initial clearance of FDOPA to striatum (KD1) was 0.07 ml g?1 min?1, and the equilibrium distribution volume (VDe) was 0.67 ml g?1. The initial clearance of O-methyl-FDOPA to striatum (KM1) was 0.08 ml g?1 min?1, and the equilibrium distribution volume (VMe) was 0.75 ml g?1. The rate constant of FDOPA decarboxylation (kD3) was 0.17 min?1 in striatum. The elimination of 6-[18F]fluorodopamine (FDA) from striatum suggested an apparent rate constant for monoamine oxidase activity (k′7) of 0.055 min?1. 6-[18F]Fluorohomovanillic acid (FHVA) was formed from 6-[18F]fluoro-l -3,4-dihydroxyphenylacetic acid with a rate constant (k11) of 0.083 min?1, and FHVA was eliminated from striatum (k9) with a rate constant of 0.12 min?1. The steady-state concentration ratios of FDA and its metabolites were shown to be functions of these rate constants. 相似文献
2.
John W. Bunting 《Bioorganic chemistry》1991,19(4)
Recent work on the reduction of heteroaromatic cations by 1,4-dihydronicotinamides and related reducing agents is reviewed. Extensive correlations are presented between the second-order rate constants (k2) for these reactions and the second-order rate constants (kOH) and equilibrium constants (pKR+) for hydroxide ion attack on these cations. Close correlations of log k2 with the electron affinities and one-electron reduction potentials of these cations are also presented. These relationships are considered in the context of a direct hydride transfer from donor to acceptor and also in terms of SET mechanisms which are also commonly discussed for such reactions. It is shown that the interpretation of these formal hydride transfer reactions in terms of an imbalanced development of electronic charge and C---H bond fission within the transition state species leads to a rational merging of the single-step hydride transfer mechanism and the SET mechanisms. The structures of the transition state species are expected to be highly variable and quite dependent upon the nature of the hydride donor and acceptor species, with considerable contribution from charge-transfer interactions. Such imbalanced transition state species are analyzed in terms of two different types of reaction coordinate diagrams and also in terms of the valence bond configuration mixing theory. 相似文献
3.
《Biocatalysis and Biotransformation》2013,31(4):377-384
AbstractThe direct electron transfer of immobilized haemoglobin (Hb) on nano-TiO2 and dodecyltrimethylammonium bromide (DTAB) film modified carbon paste electrode (CPE) and its application as a hydrogen peroxide (H2O2) biosensor were investigated. On nano-TiO2/DTAB/Hb/CPE, Hb displayed a rapid electron transfer process with participation of one proton and with an electron transfer rate constant which estimated as 0.29 s??1. Thus, the proposed biosensor exhibited a high sensitivity and excellent electrocatalytic activity for the reduction of H2O2. The catalytic reduction current of H2O2 was proportional to H2O2 concentration in the range of 0.2–4.0 mM with a detection limit of 0.07 mM. The apparent Michaelis–Menten constant (Kmapp) of the biosensor was calculated to be 0.127 mM, exhibiting a high enzymatic activity and affinity. This sensor for H2O2 can potentially be applied in determination of other reactive oxygen species as well. 相似文献
4.
[3H] quinuclidinyl benzilate (QNB), a specific muscarinic antagonist, was utilized to identify muscarinic cholinergic receptors on dispersed anterior pituitary cells. Scatchard analysis of [3H] QNB binding to receptors departs from linearity with upward concavity. A high affinity binding site having a dissociation constant (Kd) of 1.5 nM was observed when the [3H] QNB concentration was varied from 0.15 to 20 nM. A low affinity binding site (Kd 20 nM) was observed when [3H] QNB concentration was above 20 nM. Using 10 nM [3H] QNB for binding, the second order association rate constant (k1) of 0.064 nM?1 min?1 and first order dissociation rate constant (k2) of 0.078 min?1 were observed. k2/k1 = Kd of 1.22 nM is in good agreement with Kd = 1.5 nM from equilibrium data. Muscarinic cholinergic receptor antagonists, atropine and scopolamine, and agonist oxtoremorine potently competed with [3H] QNB binding. A nicotinic cholinergic receptor agonist was 50 times less potent as a competitor of [3H] QNB binding than the muscarinic agonist. 相似文献
5.
Eremin A. N. Metelitsa D. I. Moroz I. V. Pavlovskaya Zh. I. Mikhailova R. V. 《Applied Biochemistry and Microbiology》2002,38(4):322-327
A comparative kinetic study of extracellular catalases produced by Penicillium piceum F-648 and their variants adapted to H2O2 was performed in culture liquid filtrates. The specific activity of catalase, the maximum rate of catalase-induced H2O2 degradation (V
max), V
max/K
M ratio, and the catalase inactivation rate constant in the enzymatic reaction (k
in, s–1) were estimated in phosphate buffer (pH 7.4) at 30°C. The effective constant representing the rate of catalase thermal inactivation (k
in
*, s–1) was determined at 45°C. In all samples, the specific activity and K
M for catalase were maximum at a protein concentration in culture liquid filtrates of (2.5–3.5) × 10–4 mg/ml. The effective constants describing the rate of H2O2 degradation (k, s–1) were similar to that observed in the initial culture. These values reflected a twofold decrease in catalase activity in culture liquid filtrates. We hypothesized that culture liquid filtrates contain two isoforms of extracellular catalase characterized by different activities and affinities for H2O2. Catalases from variants 5 and 3 with high and low affinities for H2O2, respectively, had a greater operational stability than the enzyme from the initial culture. The method of adaptive selection for H2O2 can be used to obtain fungal variants producing extracellular catalases with improved properties. 相似文献
6.
The potentiating effects of cyanide on the inhibition of rat liver mitochondrial monoamine oxidase-A & B and of ox liver mitochondrial
MAO-B by pheniprazine [(1-methyl-2-phenylethyl)hydrazine] has been studied. Pheniprazine was shown to behave as a mechanism-based
MAO inhibitor. For rat liver MAO-B, the initial non-covalent step was characterized by dissociation constant (K
i) of 2450 nM and the first-order rate constant (k
+2) for the covalent adduct formation was 0.16 min−1. As a reversible inhibitor it was selective towards rat liver MAO-A (K
i = 420 nM) but the rate of irreversible inhibition of that enzyme was considerably slower (k
+2 = 0.06 min−1). MAO-B from ox liver more closely resembled MAO-A from the rat in sensitivity to reversible inhibition by pheniprazine (K
i = 450 nm) but it was closer to rat liver MAO-B in rate of irreversible inhibition (k
+2 = 0.29 min−1). The K
i values were significantly decreased in the presence of KCN but there was little effect on the k
+2 values. However, sensitivities of the different enzymes to KCN varied widely and considerably higher concentrations of KCN
were required for this effect to be apparent with the rat liver mitochondrial MAO-A than with MAO-B from rat and ox liver.
The kinetic behaviour of cyanide activation was consistent with partial (non-essential) competitive activation in all cases.
Special issue dedicated to Dr. Moussa Youdim. 相似文献
7.
《Inorganica chimica acta》1988,150(1):81-100
The (NH3)5CoOC(NH2)23+ ion is consumed in water according to the rate law k(obs.) = k1 + k2[OH−], where k1 = 4.0 × 10−5 s−1 and k2 = 14.2 M−1 s−1 (0–0.1 M [OH−];μ = 1.1 M, NaClO4, 25 °C). A hitherto unrecognized intramolecular O- to N- linkage isomerization reaction has been detected. In strongly acid solution only aquation to (NH3)5CoOH23+ is observed, but in 0.1–1.0 M [OH−], 7% of the directly formed products is the urea-N complex (NH3)5CoNHCONH22+ which has been isolated. In the neutral pH region a much greater proportion (25%) of the products is the urea-N species. These results are interpreted in terms of an urea-O to urea-N linkage isomerization reaction competing with hydrolysis for both spontaneous (k1) and base-catalyzed (k2) pathways; the rearrangement is not observed in strongly acidic solution (pH ⩽ 1) because the protonated N-bonded isomer (pK′a ≈ 3) is unstable with respect to the O-bonded form. The appearance of the isomerization pathway as the pH is raised in the 0–6 region is commensurate with a rate increase which cannot be attributed to a contribution from the base catalysis term k2[OH−]. It is argued that this observation establishes, for the spontaneous pathway, that hydrolysis and linkage isomerization are separate reaction pathways — there is no common intermediate. The product distribution and rate data lead to the complete rate law, k(obs.) = k1 + k2[OH−] = (ks + kON) + (kOH + k′ON) [OH−] for the reactions of the O-bonded isomers, where ks, kOH are the specific rates for hydrolysis, and kON, k′ON are the specific rates for O- to N-linkage isomerization, by spontaneous and base-catalyzed pathways respectively; kON = 1.3 × 10−5 s−1 and k′ON = 1.1 M−1 s−1 (μ = 1.0 M, NaClO4, 25 °C). The O- to N- linkage isomerization has been observed also for complexes of N-methylurea, N,N-dimethylurea and N-phenylurea, but not for the N,N′-dimethylurea species. There is an approximately statistical relationship among the data for −NH2 capture (versus H2O), while −NHR and −NR2 do not compete with water as nucleophiles for Co(III) in either the spontaneous or base-catalyzed hydrolysis processes. For each urea-O complex, O- to N-isomerization is a more significant parallel reaction in the spontaneous as opposed to the base-catalyzed pathway. This is interpreted as being indicative of more associative character in the spontaneous route to products, a conclusion supported by other evidence. Some activation parameter data have been recorded and the effect of the N-substitution on the rates of solvolysis (H2O, Me2SO) is discussed. The urea-N complexes have been isolated as their deprotonated forms, [(NH3)5CoNHCONRR′](ClO4)2·xH2O (R,R′ = H, CH3). They are kinetically inert in neutral to basic solution but in acid they protonate (H2O, pK′a 2–3; μ = 1.0 M, 25 °C) and then isomerize rapidly back to their O-bonded forms. Some solvolysis accompanies this N- to O-rearrangement in H2O and Me2SO. Specific rates and activation parameters are reported. The kinetic data follow a rate law of the form kNO(obs.) = (k + kNO)[H+]/(K′a + [H+]) and the active species in the reaction is the protonated form; k, kNO are the specific rates for hydrolysis and isomerization, respectively. Proton NMR data establish that the site of protonation (in Me2SO) is the cobalt-bound nitrogen atom. For the unsubstituted urea species (NH3)5CoNH2CONH23+, diastereotopic exo-NH2 protons arising from restricted rotation about the CN bond are observed. The relevance to the mechanism of the linkage isomerization process is considered. 13C and 1H NMR and electronic absorption spectral data are presented, and distinctions between linkage isomers and the solution structures (electronic and conformational) are discussed. The urea-N/urea-O complex equilibrium is governed by the relation K′NO(obs.) = K′NO[H+]/[H+](K′a), where K′NO is the equilibrium constant = [(NH35Co(urea-O)3+]/[(NH3)5Co(urea-N)3+]. Values for K′NO(=kNO/kON = 260 and pK′a ≈ 3 for the NH2CONH2 system are consistent with the stability of the N-isomer in feebly acidic to basic solution (e.g. pH 6, K′NO(obs.) = 2.6 × 10−2) and instability in acid solution (e.g. pH 1, K′NO(obs.) = 240). The equilibrium data for this and other urea complexes of (NH3)5Co(III) are contrasted with the result for the analogous Rh(III)NH2CONH2 system K′NO ≈ 1). 相似文献
8.
Although quinones represent a class of organic compounds that may exert toxic effects both in vitro and in vivo, the molecular mechanisms involved in quinone species toxicity are still largely unknown, especially in the presence of transition metals, which may both induce the transformation of the various quinone species and result in generation of harmful reactive oxygen species. In this study, the oxidation of 1,4-naphthohydroquinone (NH2Q) in the absence and presence of nanomolar concentrations of Cu(II) in 10 mM NaCl solution over a pH range of 6.5–7.5 has been investigated, with detailed kinetic models developed to describe the predominant mechanisms operative in these systems. In the absence of copper, the apparent oxidation rate of NH2Q increased with increasing pH and initial NH2Q concentration, with concomitant oxygen consumption and peroxide generation. The doubly dissociated species, NQ2−, has been shown to be the reactive species with regard to the one-electron oxidation by O2 and comproportionation with the quinone species, both generating the semiquinone radical (NSQ−). The oxidation of NSQ− by O2 is shown to be the most important pathway for superoxide (O2−) generation with a high intrinsic rate constant of 1.0×108 M−1 s−1. Both NSQ− and O2− served as chain-propagating species in the autoxidation of NH2Q. Cu(II) is capable of catalyzing the oxidation of NH2Q in the presence of O2 with the oxidation also accelerated by increasing the pH. Both the uncharged (NH2Q0) and the mono-anionic (NHQ−) species were found to be the kinetically active forms, reducing Cu(II) with an intrinsic rate constant of 4.0×104 and 1.2×107 M−1 s−1, respectively. The presence of O2 facilitated the catalytic role of Cu(II) by rapidly regenerating Cu(II) via continuous oxidation of Cu(I) and also by efficient removal of NSQ− resulting in the generation of O2−. The half-cell reduction potentials of various redox couples at neutral pH indicated good agreement between thermodynamic and kinetic considerations for various key reactions involved, further validating the proposed mechanisms involved in both the autoxidation and the copper-catalyzed oxidation of NH2Q in circumneutral pH solutions. 相似文献
9.
Summary. The kinetic aspects of the Perinaphthenone-sensitized photooxidation (singlet molecular oxygen [O2 (1Δg)]-mediated) of α-chymotrypsin (α-Chymo) have been studied at pH 8 and pH 11 as well in reverse micelles (RMs) of sodium 1,
4 bis (2-ethylhexyl) sulfosuccinate (AOT) in n-heptane.
The rate constant values for both overall (kt) and chemical (kr) quenching of O2 (1Δg) by α-Chymo in homogeneous media were higher at pH = 11 than at pH = 8, indicating that the OH-ionized tyrosine (Tyr) residues,
clearly dominate the quenching process. Besides, the rate constants in water were higher than those determined in RMs, demonstrating
that the organized medium protects the protein against photooxidation, probably due to a diminution in both, the accessibility
towards oxidizable amino acid residues and the polarity inside the aggregate, as compared to water. The protection effect
of α-Chymo against the attack by the oxidative species O2 (1Δg) in RMs of AOT seems to be due to the increase of protein stability by the encapsulation within the micellar structure.
The effect of both, surfactant concentration and variation of the ratio ([H2O]/[AOT]) = W on the reactive rate constant was also investigated. The process does not depend significantly on micelles concentration
while the kr values increase as W increases. Furthermore, at W = 30, the highest W studied, kr tends to the value obtained in aqueous medium.
Authors’ address: M. A. Biasutti, Departamento de Química, Campus Universitario, Universidad Nacional de Río Cuarto, (X5804ALH)
Río Cuarto, Argentina 相似文献
10.
The cytochrome b
6
f (Cyt b
6
f) complex, which functions as a plastoquinol-plastocyanin oxidoreductase and mediates the linear electron flow between photosystem
II (PSII) and photosystem I (PSI) and the cyclic electron flow around PSI, was isolated from spinach (Spinacia oleracea L.) chloroplasts using n-octyl-β-D-glucopyranoside (β-OG). The preparation was also able to catalyze the peroxidase-like reaction in the presence
of hydrogen peroxide (H2O2) and guaiacol. The optimal conditions for peroxidase activity of the preparation included: pH 3.6, ionic strength 0.1, and
temperature 35°C. The apparent Michaelis constant (K
m) values for H2O2 and guaiacol were 50 mM and 2 mM, respectively. The bimolecular rate constant (k
obs) was about 26 M−1 s−1 and the turnover number (K
cat) was about 60 min−1 (20 mM guaiacol, 100 mM sodium phosphate, pH 3.6, 25°C, [H2O2]<100mM). These parameters were similar to those of several other heme-containing proteins, such as myoglobin and Cyt c. 相似文献
11.
We have compared the effect of ethanol, a membrane perturbant, on the muscarinic binding sites in neural membranes from a vertebrate (rat) and an insect (locust). The binding of the muscarinic antagonist [3H]quinuclidinyl benzilate ([3H]QNB) to both rat and locust neural membranes was inhibited by ethanol at 10–500 mM concentrations; but this inhibition was greater in the locust. Ethanol (500 mM) increased the apparent dissociation constant (K
d) of [3H]QNB binding to rat membranes from 0.13±0.01 nM in control to 0.20±0.02 nM; there was also an small but significant reduction in the number of binding sitesB
max. In locust, 500 mM ethanol reduced theB
max of [3H]QNB binding from 590±30 in control to 320±40 pmol/g protein; no significant alteration in theK
D was detected. The dissociation rate constant (k
off) of [3H]QNB increased from 0.020±0.003 in controls to 0.031±0.004 (min–1) in the presence of 500mM ethanol, the association rate constant (k
on) did not change significantly. In locust, 500 mM ethanol did not affect eitherk
on ork
off. Competition experiments revealed that the binding affinities of both the agonist carbamylcholine and the antagonist atropine to the rat membranes were reduced in the presence of ethanol. In contrast, ethanol caused no alteration in the binding affinities of these ligands to the locust membranes. This differential effect of ethanol on rat and locust muscarinic binding suggests a difference in the hydrophobic domains and/or the membrane interactions of the muscarinic receptors in the two species. 相似文献
12.
The rate of reaction of [Cr(III)Y]aq (Y is EDTA anion) with hydrogen peroxide was studied in aqueous nitrate media [μ = 0.10 M (KNO3)] at various temperatures. The general rate equation, Rate = [Cr(III)Y]aq[H2O2] holds over the pH range 5–9. The decomposition reaction of H2O2 is believed to proceed via two pathways where both the aquo and hydroxo-quinquedentate EDTA complexes are acting as the catalyst centres. Substitution-controlled mechanisms are suggested and the values of the second-order rate constants k1 and k2 were found to be 1.75 × 10?2 M?1 s?1 and 0.174 M?1 s?1 at 303 K respectively, where k2 is the rate constant for the aquo species and k2 is that for the hydroxo complex. The respective activation enthalpies (ΔH*1 = 58.9 and ΔH*2 = 66.5 KJ mol?1) and activation entropies (ΔS*1 = ?85 and ΔS*2 = ?40 J mol?1 deg?1) were calculated from a least-squares fit to the Eyring plot. The ionisation constant pK1, was inferred from the kinetic data at 303 K to be 7.22. Beyond pH 9, the reaction is markedly retarded and ceases completely at pH ? 11. This inhibition was attributed in part to the continuous loss of the catalyst as a result of the simultaneous oxidation of Cr(III) to Cr(VI). 相似文献
13.
M. V. Potapovich A. N. Eryomin I. M. Artzukevich I. P. Chernikevich D. I. Metelitza 《Biochemistry. Biokhimii?a》2001,66(6):646-657
Catalase (CATpp) with molecular weight 223 kD was isolated from the methylotrophic yeast Pichia pastoris and purified 90-fold by ion-exchange chromatography and gel filtration. Quantitative parameters of absorption and CD spectra of CATpp solutions and of its membrane-concentrated form (CATpp-conc) were studied. Rates of H2O2 decomposition and kinetic characteristics K
m and k
cat of CATpp and CATpp-conc were determined in 10 mM phosphate buffer (pH 7.4) at 30°C, as well as the effective constant k
in of the enzyme inactivation rate during the catalysis and the constant k
2 of the interaction rate of the Complex I catalases with H2O2. Thermal inactivation of CATpp in solutions at 45°C was characterized by the effective rate constant k
in
*, and the low-frequency (27 kHz) ultrasonic inactivation of CATpp at 20°C was characterized by the firstorder rate constant k
in (US). All spectral and kinetic characteristics of CATpp and CATpp-conc were compared with the corresponding values for catalase from bovine liver (CAT) and for catalase from the methylotrophic yeast Candida boidinii (CATcb). All three catalases were rather similar in their spectral properties but strongly varied in their kinetic parameters, and their comparison suggests that CATpp should be the best enzyme in its overall properties as it displayed the maximal efficiency in terms of k
cat/K
m, thermal stability comparable with the thermal stability of CAT in terms of k
in
*, the minimal k
in, and high stability in the ultrasonic cavitation field at the US power of 60 W/cm2. 相似文献
14.
Reactive nitrogen intermediates are synthesized by activated macrophages. These molecules, and nitrous anhydride (N2O3) in particular, are known to be potent nitrosylating species. We investigated the role of macrophage-derived N2O3 in extracellular nitrosylation. We used dilution experiments to demonstrate the intracellular production of N2O3 and its export into the extracellular medium, with a rate constant kex = 6.8 × 106 M s−1. The kinetics of the competition between extracellular hydrolysis of N2O3 and its reaction with added glutathione were also studied. We obtained a value of the rate constant kGSH for the latter reaction of 4.4 × 107 M−1 s−1, consistent with earlier determinations in cell-free systems. The implications of these results in human albumin nitrosylation were investigated. Nitrosylated albumin was detected in activated macrophages supernatants using an anti-NO-acetylated cysteine antibody. It was estimated that 10% of N2O3 produced by activated cells participate in extracellular nitrosylation. N2O3 thus appears to be a new effector molecule of the immune system, as an agent for the nitrosylation of albumin, the main nitric oxide carrier in vivo. 相似文献
15.
The rate of reaction between superoxide anion (O¯.2) and 1,2-dihydroxybenzene-3,5-disulfonic acid (tiron) was measured with pulse radiolysis-generated O¯.2. A kinetic spectrophotometric method utilizing competition betweenp-benzoquinoneand tiron for O¯.2 was employed. In this system, the known rate of reduction ofp-benzoquinonewas compared with the rate of oxidation of tiron to the semiquinone. From the concentration dependence of the rate of tiron oxidation, the absolute second order rate constant for the reaction was determined to be 5 · 108 M?·s?1. Ascorbat reduced O¯.2 to hydrogen peroxide with a rate constant of 108 M?1 · s?1 as determined by the same method. The tiron semiquinone may be used as an indicator free radical for the formation of superoxide anion in biological systems because of the rapid rate of oxidation of the catechol by O¯.2 compared to the rate of O¯.2 formation in most enzymatic systems.Tiron oxidation was used to follow the formation of superoxide anion in swollen chloroplasts. The chloroplasts photochemically reduced molecular oxygen which was further reduced to hydrogen peroxide by tiron. Tiron oxidation specifically required O¯.2 since O2 was consumed in the reaction and tiron did not reduce the P700 cation radical or other components of Photosystem I under anaerobic conditions. 相似文献
16.
Enzyme production in a cell recycle fermentation system was studied by computer simulations, using a mathematical model of -amylase production by Bacillus amyloliquefaciens. The model was modified so as to enable simulation of enzyme production by hypothetical organisms having different production kinetics at different fermentation conditions important for growth and production. The simulations were designed as a two-level factorial assay, the factor studied being fermentation with or without cell recycling, repression of product synthesis by glucose, kinetic production constants, product degradation by a protease, mode of fermentation, and starch versus glucose as the substrate carbon source.The main factor of importance for ensuring high enzyme production was cell recycling. Product formation kinetics related to the stationary growth phase combined with continuous fermentation with cell recycling also had a positive impact. The effect was greatest when two or more of these three factors were present in combinations, none of them alone guaranteeing a good result. Product degradation by a protease decreased the amount of product obtained; however, when combined with cell recycling, the protease effect was overshadowed by the increased production. Simulation of this type should prove a useful tool for analyzing troublesome fermentations and for identifying production organisms for further study in integrated fermentation systems.List of Symbols
a
proportionality constant relating the specific growth rate to the logarithm of G (h)
-
a
1
reaction order with respect to starch concentration
-
a
2
reaction order with respect to glucose concentration
-
c
starch concentration (g/l)
-
c
0
starch concentration in the feed (g/l)
-
D
dilution rate (h–1)
-
e
intrinsic intracellular amylase concentration (g product/g cell mass)
-
E
extracellular amylase concentration (g/l)
-
F
volumetric flow rate (l/h)
-
G
average number of genome equivalents of DNA/cell
-
K
1
intracellular repression constant
-
K
2
intracellular repression constant
-
K
s
Monod saturation constant (g/l)
-
k
3
product excretion rate constant (h–1)
-
k
I
translation constant (g product/g mRNA/h)
-
k
d
first order decay constant (h–1)
-
k
dw
first order decay constant (h–1)
-
k
gl
rate constant for glucose production (g/l/h)
-
k
m, dgr
saturation constant for product degradation (g/l)
-
k
st
rate constant for starch hydrolysis (g/l/h)
-
k
t1
proportionality constant for amylase production (g mRNA/g substrate)
-
k
t2
proportionality constant for amylase production (g mRNA *h/g substrate)
-
k
w
protease excretion rate constant (h–1)
-
k
wt1
proportionality constant for protease production (g mRNA/g substrate)
-
k
wt2
proportionality constant for protease production (g mRNA *h/g substrate)
-
k
wI
translation constant (g protease/g mRNA/h)
-
m
maintenance coefficient (g substrate/g cell mass/h)
-
n
number of binding sites for the co-repressor on the cytoplasmic repressor
-
Q
repression function, K1/K2 less than or equal to 1.0
-
Q
w
repression function, K1/K2 less than or equal to 1.0
-
r
intrinsic amylase mRNA concentration (g mRNA/g cell mass)
-
r
m
intrinsic protease mRNA concentration (g mRNA/g cell mass)
-
R
ex
retention by the filter of the compounds x=: C starch, E amylase, or S glucose
-
R
t
amylase transport rate (g product/g cell mass/h)
-
R
wt
protease transport rate (g protease/g cell mass/h)
-
R
s
rate of glucose production (g/l/h)
-
R
c
rate of starch hydrolysis (g/l/h)
-
S
0
feed concentration of free reducing sugar (g/l)
-
s
extracellular concentration of reducing sugar (g/l)
-
t
time (h)
-
V
volume (1)
-
w
intracellular protease concentration (g/l)
-
W
extracellular protease concentration (g/l)
-
X
cell mass concentration (dry weight) (g/l)
-
Y
yield coefficient (g cell mass/g substrate)
-
substrate uptake (g substrate/g cell mass/h)
-
specific growth rate of cell mass (h–1)
-
d
specific death rate of cells (h–1)
-
m
maximum specific growth rate of cell mass (h–1)
-
m,dgr
maximum specific rate of amylase degradation (h–1)
This study was supported by the Nordic Industrial Foundation Bioprocess Engineering Programme and the Center for Process Biotechnology, The Technical University of Denmark. 相似文献
17.
Summary The influence of temperature on the growth of the theromophilic Bacillus caldotenax was investigated using chemostat techniques and a chemically defined minimal medium. All determined growth constants, that is maximal specific growth rate, yield and maintenance, were temperature dependent. It was striking that the very large maintenance requirement was about 10 times higher than for mesophilic cells under equivalent conditions. A death rate, which was very substantial at optimal and supraoptimal growth temperatures, was estimated by comparing the maintenance for substrate and oxygen. There was no indication for a thermoadaptation as postulated by Haberstich and Zuber (1974).Symbols D
Dilution rate (h–1)
- Dc=max
Critical dilution rate (h–1)
- E
Temperature characteristic (J mol–1)
- k
Organism constant
- kd
Death rate coefficient (h–1)
- km
Maintenance substrate coefficient estimated from MO (h–1)
- MO
Maintenance respiration, mmol O2 per g dry biomass and h (mmol g–1h–1)
- MO
Maintenance respiration, taking kd into account
- mS
Maintenance substrate coefficient, g glucose per g dry biomass and h (h–1)
- OD
Optical density at 546 nm
- QO2
Specific O2-uptake rate (mmol g–1h–1)
- Q
O2
V
Specific O2-uptake rate for viable portion of biomass (mmol g–1 h–1)
- QS
Specific glucose uptake rate (h–1)
- Q
S
V
Specific glucose uptake rate for viable portion of biomass (h–1)
- R
Gas constant 8.28 J mol–1K–1
- S
Substrate concentration in reactor (g l–1)
- SO
Influent substrate concentration (g l–1)
- Tmax
Maximal growth temperature (°C)
- Tmin
Minimal growth temperature (°C)
- X
Dry biomass (g l–1)
- XtOt=X
Dry biomass containing dead and viable cells
- Xv
Viable portion of biomass
- Y
O
m
Potential yield for O2 corrected for maintenance respiration (g mol–1)
- Y
S
m
Potential yield for substrate corrected for maintenance requirement, g biomass per g glucose (–)
-
Specific growth rate (h–1)
- max
Maximal specific growth rate (h–1) 相似文献
18.
A. N. Eryomin M. V. Makarenko L. A. Zhukovskaya R. V. Mikhailova 《Applied Biochemistry and Microbiology》2006,42(3):304-311
Hydroxides of magnesium and zinc, aluminum oxide, zinc phosphate, and co-precipitated Ca3(PO4)2 and Mg(OH)2 were efficient in binding extracellular glucose oxidase (GO) of P. adametzii LF F-2044.1 in a culture liquid filtrate (CLF). Basic Al2O3 was the most appropriate adsorbent for GO isolation from the CLF of the fungus. A GO isolation method was developed, which allowed for obtaining an enzyme with a high degree of purification. Spectral properties of the enzyme, its catalytic activity, and stability were characterized. The GO of P. adametzii LF F-2044.1 exhibited high pH stability, retaining activity within the range 4.5–9.0. The rate that GO-catalyzed D-glucose oxidation increased as the temperature increased (up to approximately 60°C). The catalytic activity and thermal stability of GO depended on its concentration in the medium. Under optimum conditions, the fractions GO-1 and GO-2 were characterized by K M values of 1.56 × 10?2 and 2.19 × 10?2 M, respectively; the corresponding values of k cat equaled 235.1 and 318.2 s?1. 相似文献
19.
M. L. F. Giuseppin 《Applied microbiology and biotechnology》1984,20(3):161-165
Summary The influence of the concentration of oxygen on lipase production by the fungus Rhizopus delemar was studied in different fermenters. The effect of oxygen limitation ( 47 mol/l) on lipase production by R. delemar is large as could be demonstrated in pellet and filamentous cultures. A model is proposed to describe the extent of oxygen limitation in pellet cultures. Model estimates indicate that oxygen is the limiting substrate in shake flask cultures and that an optimal inoculum size for oxygen-dependent processes can occur.Low oxygen concentrations greatly negatively affect the metabolism of R. delemar, which could be shown by cultivation in continuous cultures in filamentous growth form (Doptimal=0.086 h-1). Continuous cultivations of R. delemar at constant, low-oxygen concentrations are a useful tool to scale down fermentation processes in cases where a transient or local oxygen limitation occurs.Symbols and Abbreviations CO
Oxygen concentration in the gas phase at time = 0 (kg·m-3)
- CO
2i
Oxygen concentration at the pellet liquid interface (kg·m-3)
- CO
2i
Oxygen concentration in the bulk (kg·m-3)
-
D
Dilution rate (h-1)
- IDO
2
Diffusion coefficient for oxygen (m2·s-1)
-
dw
Dry weight of biomass (kg)
-
f
Conversion factor (rs
O
2 to oxygen consumption rate per m3) (-)
-
k
Radial growth rate (m·s-1)
-
K
Constant
-
kla
Volumetric mass transfer coefficient (s-1)
-
klA
Oxygen transfer rate (m-3·s-1)
-
kl
Mass transfer coefficient (m·s-1)
-
K
O
2
Affinity constant for oxygen (mol·m-3)
-
K
w
Cotton plug resistance (m-3·s-1)
-
M
Henry coefficient (-)
-
NV
Number of pellets per volume (m-3)
-
R
Radius (m)
-
RO
Radius of oxygen-deficient core (m)
-
RQ
Respiration quotient (mol CO2/mol O2)
-
rs
O
2
Specific oxygen consumption rate per dry weight biomass (kg O2·s-1[kg dw]-1)
-
rX
Biomass production rate (kg·m-3·s-1)
-
SG
Soytone glucose medium (for shake flask experiments)
-
SG
4
Soytone glucose medium (for tower fermenter and continuous culture experiments)
-
V
Volume of medium (m-3)
-
X
Biomass (dry weight) concentration (kg·m-3)
-
XR
o
Biomass concentration within RO for a given X (kg·m-3)
-
Y
O
2
Biomass yield calculated on oxygen (kg dw/kg O2)
-
Thiele modulus
-
Efficiency factor =1-(RO/R)3 (-)
-
Growth rate (m-1·s-1·kg1/3)
-
Dry weight per volume of pellet (kg·m-3) 相似文献
20.
Myung-Yeol Lee Chang-Won SuhYong-Tae Ahn Hang-Sik Shin 《Bioresource technology》2009,100(11):2816-2822
The objective of the study was to examine the application of the Anaerobic Digestion Model No. 1 (ADM1) developed by the IWA task group for mathematical modelling of anaerobic process. Lab-scale temperature-phased anaerobic digestion (TPAD) process were operated continuously, and were fed with co-substrate composed of dog food and flour. The model platform implemented in the simulation was a derivative of the ADM1. Sensitivity analysis showed that km.process (maximum specific uptake rate) and KS.process (half saturation value) had high sensitivities to model components. Important parameters including maximum uptake rate for propionate utilisers (km.pro) and half saturation constant for acetate utilisers (KS.ac) in the thermophilic digester and maximum uptake rate for acetate utilisers (km.ac) in the mesophilic digester were estimated using iterative methods, which optimized the parameters with experimental results. Simulation with estimated parameters showed good agreement with experimental results in the case of methane production, uptake of acetate, soluble chemical oxygen demand (SCOD) and total chemical oxygen demand (TCOD). Under these conditions, the model predicted reasonably well the dynamic behavior of the TPAD process for verifying the model. 相似文献