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1.
Hydrogenase was solubilized from the membrane of acetate-grown Methanosarcina barkeri MS and purification was carried out under aerobic conditions. The enzyme was reactivated under reducing conditions in the presence of H2. The enzyme showed a maximal activity of 120±40 mol H2 oxidized · min–1 · min–1 with methyl viologen as an electron acceptor, a maximal hydrogen production rate of 45±4 mol H2 · min–1 · mg–1 with methyl viologen as electron donor, and an apparent K
m for hydrogen oxidation of 5.6±1.7 M. The molecular weight estimated by gel filtration was 98,000. SDS-PAGE showed the enzyme to consist of two polypeptides of 57,000 and 35,000 present in a 1:1 ratio. The native protein contained 8±2 mol Fe, 8±2 mol S2–, and 0.5 mol Ni/mol enzyme. Cytochrome b was reduced by hydrogen in a solubilized membrane preparation. The hydrogenase did not couple with autologous F420 or ferredoxin, nor with FAD, FMN, or NAD(P)+. The physiological function of the membrane-bound hydrogenase in hydrogen consumption is discussed.Abbreviation CoM-S-S-HTP
the heterodisulfide of 7-mercaptoheptanoylthrconine phosphate and coenzyme M (mercaptoethanesulfonic acid) 相似文献
2.
Christian Wandrey Werner Hönig Maria-Regina Kula 《Applied microbiology and biotechnology》1977,3(4):257-265
Summary A new, sensitive and continuous assay for -glucosidase is described exploiting the different angles of rotation for the substrate maltose and the product glucose. Kinetic experiments revealed a very pronounced product inhibition of -glucosidase fromSaccharomyces carlsbergensis with a Ki of 4.85·10–3 M for glucose.The KM of maltose was found to be 37.8·10–3 M. Taking these values, an integral kinetic curve for the enzymatic hydrolysis of maltose was calculated, which is shown to fit the experimental data.Symbols used k1 (min–1)
pseudo first-order rate constant (for enzymatic cleavage)
- k2 (min–1)
rate constant (for mutarotation reaction)
- I, P (mol/1)
inhibitor (product) concentration
- ki (mmol/1)
inhibitor constant
- KM (mmol/l)
Michaelis constant
- [M]
589
30
(degree/m · l/mol)
molecular rotation at 30°C and 589 nm
- s (mmol/l)
substrate concentration
- R (mmol/mg · min)
reaction rate
- Vmax (mmol/mg · min)
maximal rate
- U (mol/min)
activity unit (here at 30°C and pH=6.8)
Indices O
initial value
- max
maximal value 相似文献
3.
In rat cardiac sarcolemmal membranes a phosphoinositide-specific phospholipase C (PLC) was found to be present. The enzyme hydrolysed exogenous [3H-]phosphatidylinositol 4,5-biphosphate ([3H-]PtdIns(4,5)P
2) in an optimized assay mixture containing 15 leg SL protein, 100 mM NaCl, 1 mM free Ca2+,14 mM Na-cholate and 20 AM [3H-]PtdIns (4,5)P
2 (400–500 dpm/gm-l) in 30 mM HEPES-Tris buffer (pH 7.0). The average specific activity was 9.14±0.55 nmol-mg–1·2.5 min–1. The addition of Mg2+ to the assay mixture did not change PLC activity but increased the relative amounts of dephosphorylated inositol products. In the absence of Na+ and at a low Ca2+ concentration (0.3 M), Mg2+ also enhanced the intraSL levels of PtdIns4P and PtdIns, and, moreover, inhibited PLC activity (IC500.07 mM). PtdIns4P seemd to be a good substrate for the rat SL PLC (23.07 ± 1.57 nmol·mg–1·2.5 min–1) whereas PtdIns was hydrolysed at a very low rate (0.36 ± 0.08 nmol·mg–1·2.5 min–1). Unlike PtdIns(4,5)P
2, PLC-dependent PtdIns4P and PtdIns hydrolysis was not inhibited by Ca2+ concentrations over 1 mM. The possibility of distinct isozymes being responsible for the different hydrolytic activities is discussed. (Mol Cell Biochem116: 27–31, 1992).Abbreviations DAG
sn-1,2-diacylglycerol
- EGTA
ethyleneglycol-O,O-bis(aminoethyl)-N,N,N,N,-tetraacetic acid
- Ins(1,4,5)P
3
inositol 1,4,5-trisphosphate
- InsP
inositol monophosphate (unidentified isomer)
- InsP
2
inositol bisphosphate (unidentified isomer)
- InsP
3
inositol trisphosphate (unidentified isomer)
- InsP
x
any inositol phosphate
- PLC
phospholipase C
- PtdIns
phosphatidylinositol
- PtdIns(4,5)P
2
phosphatidylinositol 4,5-bisphosphate
- PtdIns4P
phosphatidylinositol 4-monophosphate
- SL
sarcolemma 相似文献
4.
The stability and, consequently, the lifetime of immobilized enzymes (IME) are important factors in practical applications of IME, especially so far as design and operation of the enzyme reactors are concerned. In this paper a model is presented which describes the effect of intraparticle diffusion on time stability behaviour of IME, and which has been verified experimentally by the two-substrate enzymic reaction. As a model reaction the ethanol oxidation catalysed by immobilized yeast alcohol dehydrogenase was chosen. The reaction was performed in the batch-recycle reactor at 303 K and pH-value 8.9, under the conditions of high ethanol concentration and low coenzyme (NAD+) concentration, so that NAD+ was the limiting substrate. The values of the apparent and intrinsic deactivation constant as well as the apparent relative lifetime of the enzyme were calculated.The results show that the diffusional resistance influences the time stability of the IME catalyst and that IME appears to be more stabilized under the larger diffusion resistance.List of Symbols
C
A, CB, CE mol · m–3
concentration of coenzyme NAD+, ethanol and enzyme, respectively
-
C
p mol · m3
concentration of reaction product NADH
-
d
p mm
particle diameter
-
D
eff m2 · s–1
effective volume diffusivity of NAD+ within porous matrix
-
k
d s–1
intrinsic deactivation constant
-
K
A, KA, KB mol · m–3
kinetic constant defined by Eq. (1)
-
K
A
x
mol · m–3
kinetic constant defined by Eq. (5)
-
r
A mol · m–3 · s–1
intrinsic reaction rate
-
R m
particle radius
-
R
v mol · m–3 · s–1
observed reaction rate per unit volume of immobilized enzyme
-
t
E s
enzyme deactivation time
-
t
r s
reaction time
-
V mol · m–3 · s–1
maximum reaction rate in Eq. (1)
-
V
x mol · m–3 · s–1
parameter defined by Eq. (4)
-
V
f m3
total volume of fluid in reactor
-
w
s kg
mass of immobilized enzyme bed
-
factor defined by Eqs. (19) and (20)
-
kg · m–3
density of immobilized enzyme bed
-
unstableness factor
-
effectiveness factor
-
Thiele modulus
-
relative half-lifetime of immobilized enzyme
Index
o
values obtained with fresh immobilized enzyme 相似文献
5.
A modified Rotating Biological Contactor (RBC) was used for the treatability studies of synthetic tapioca wastewaters. The RBC used was a four stage laboratory model and the discs were modified by attaching porous nechlon sheets to enhance biofilm area. Synthetic tapioca wastewaters were prepared with influent concentrations from 927 to 3600 mg/l of COD. Three hydraulic loads were used in the range of 0.03 to 0.09 m3·m–2·d–1 and the organic loads used were in the range of 28 to 306 g COD· m–2·d–1. The percentage COD removal were in the range from 97.4 to 68. RBC was operated at a rotating speed of 18 rpm which was found to be the optimal rotating speed. Biokinetic coefficients based on Kornegay and Hudson models were obtained using linear analysis. Also, a mathematical model was proposed using regression analysis.List of Symbols
A m2
total surface area of discs
-
d m
active depth of microbial film onany rotating disc
-
K
s mg ·l–1
saturation constant
-
P mg·m–2·–1
area capacity
-
Q l·d–1
hydraulic flow rate
-
q m3·m–2·d–1
hydraulic loading rate
-
S
0 mg·l–1
influent substrate concentration
-
S
e mg·l–1
effluent substrate concentration
-
w rpm
rotational speed
-
V m3
volume of the reactor
-
X
f mg·l–1
active biomass per unit volume ofattached growth
-
X
s mg·l–1
active biomass per unit volume ofsuspended growth
-
X mg·l–1
active biomass per unit volume
-
Y
s
yield coefficient for attachedgrowth
-
Y
A
yield coefficient for suspendedgrowth
-
Y
yield coefficient, mass of biomass/mass of substrate removed
Greek Symbols
hr
mean hydraulic detention time
- (max)A d–1
maximum specific growth rate forattached growth
- (max)s d–1
maximum specific growth rate forsuspended growth
- max d–1
maximum specific growth rate
- d–1
specific growth rate
- v mg·l–1·hr–1
maximum volumetric substrateutilization rate coefficient 相似文献
6.
Summary Some environmental affects on cell aggregation described in the literature are briefly summarized. By means of a biomass recirculation culture (Contact system), using the yeast Torulopsis glabrata, the aggregation behavior of cells in static and in dynamic test systems is described. Sedimentation times required to obtain 50 g · l–1 yeast dry matter in static systems were always higher than in dynamic ones.In addition to, influencing the biomass yield, the specific growth rate of the yeast also affected cell aggregation. The specific growth rate and therefore the aggregation could be regulated by the biomass recirculation rate as well as by the sedimenter volume.Abbreviations fo
Overflow flow rate (l·h–1)
- fR
Recycle flow rate (l·h–1)
- ft0t
Total flow rate through the fermenter (l·h–1)
- g
Gram
- h
Hour
- DR
Fermenter dilution rate due to recycle (h–1)
- DS
Fermeter dilution rate due to substrate (h–1)
- Dtot
Total fermenter dilution rate (h–1)
- l
Liter
-
Specific growth rate (h–1)
- PF
Fermenter productivity (g·l–1·h–1)
- PFS
Overall productivity (g·l–1·h–1)
- RpM
Rates per minute
- RS
Residual sugar content in the effluent with respect to the substrate concentration (%)
- Y
Yield of biomass with respect to sugar concentration (%)
-
Sed 50
Sedimentation time to reach a YDM of 50 g·l–1 (min)
- V
Volume (l)
- VF
Fermenter volume (l)
- VSed
Sedimenter volume (l)
- VVM
Volumes per volume and minute
- XF
YDM in the fermenter (g·l–1)
- XF
YDM in the recycle (g·l–1)
- XS
Yeast dry matter due to substrate concentration (g·l–1)
- YDM
Yeast dry matter (g·l–1) 相似文献
7.
Summary
Chaetomium cellulolyticum (ATCC 32319) was cultivated on glucose, Avicel and/or Sigmacell in a 20-1 stirred tank batch reactor. The substrate (cellulose) concentration, the cell mass concentration (through protein and/or nitrogen content), reducing sugar concentration, the enzyme activity, the alkali consumption rate, the dissolved O2 and CO2 concentrations in the outlet gas were measured. The specific growth rate, the substrate yield coefficient, cell productivity, the oxygen consumption rate, the CO2 production rate and the volumetric mass transfer coefficient were determined. At the beginning of the growth phase the oxygen utilization rate exhibits a sharp maximum. This maximum could be used to start process control. Because of the long lag phase periodic batch operation is recommended.Symbols CP
cell protein concentration (g l–1)
- FPA
FP enzyme activity (IU l–1)
- GP
dissolved protein concentration (g l–1)
- IU
international unit of enzyme activity
- kLa
volumetric mass tranfer coefficient (h–1)
- LG
alkali (1 n NaOH) consumption (ml)
- LGX
specific alkali consumption rate per cell mass (ml g–1 h–1)
- P
cell mass productivity (g l–1 h–1)
-
specific oxygen consumption rate per cell mass (g g–1 h–1)
- Q
aeration rate (volumetric gas flow rate per volume of medium, vvm) (min–1)
- N
impeller speed (revolution per minute, rpm) (min–1)
- S
substrate concentration (g l–1)
- S0
S at tF=0 (g l–1)
- S0
S in feed (g l–1)
- SR
acid consumption (ml)
- TDW
total dry weight (g l–1)
- T
temperature (° C)
- tF
cultivation time (h)
- U
substrate conversion
- X
cell mass concentration (g l–1)
- YX/S
vield coefficient
-
specific growth rate (h–1)
- m
maximum specific growth rate (h–1) 相似文献
8.
Lactate content and lactate dehydrogenase activity inPalaemon serratus abdominal muscle during temperature changes 总被引:1,自引:1,他引:0
M. T. Thébault 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1984,154(1):85-89
Summary Lactate concentration was measured in the abdominal muscle of the shrimpPalaemon serratus. Rapid and seasonal temperature changes result in an increase of the lactate content of approximately 3–4 fold.Lactate dehydrogenase from the abdominal muscle exhibits a temperature dependent pyruvate inhibition with pyruvate as substrate.The kinetic parameters of lactate dehydrogenase fromPalaemon serratus are found to vary during rapid temperature changes: Vmax increases with temperature from 0.06 mol min–1 (mg protein)–1 at 10°C to 0.28 mol min–1 (mg protein)–1 at 30°C with lactate as substrate, and from 5.5 mol min–1 (mg protein)–1 at 10°C to 26.2 mol min–1 (mg protein)–1 at 30°C, with pyruvate (Table 1). The Hill coefficientn
H, decreases with temperature from 2.2 to 1.2 when the pyruvate reduction is examined, but remains near 1.2 when the activity is measured with lactate as substrate (Table 1). The S0.5 values for lactate show a tendency to increase below 30 °C (18.9 mM l–1 at 20 °C) whereas the S0.5 for pyruvate is found to increase greatly with temperature (0.004 mM l–1 at 10 °C and 0.06 mM l–1 at 20 °C).Long term temperature changes involve variations of lactate dehydrogenase activity leading to inverse thermal compensation (Table 2).Activation energy (about 56 kJ both with pyruvate and lactate) does not vary during the year, suggesting that temperature adaptation does not induce important catalytic changes (Table 3).Abbreviation LDH
lactate dehydrogenase 相似文献
9.
Glutathione reductase activity was detected and characterized in heterocysts and vegetative cells of the cyanobacterium Nostoc muscorum. The activity of the enzyme varied between 50 and 150 nmol reduced glutathione· min-1·mg protein-1, and the apparent Km for NADPH was 0.125 and 0.200 mM for heterocysts and vegetative cells, respectively. The enzyme was found to be sensitive to Zn+2 ions, however, preincubation with oxidized glutathione rendered its resistance to Zn+2 inhibition. Nostoc muscorum filaments were found to contain 0.6–0.7mM glutathione, and it is suggested that glutathione reductase can regenerate reduced glutathione in both cell types. The combined activity of glutathione reductase and isocitrate dehydrogenase in heterocysts was as high as 18 nmol reduced glutathione·min-1·mg protein-1. A relatively high superoxide dismutase activity was found in the two cell types; 34.2 and 64.3 enzyme units·min-1·mg protein-1 in heterocysts and vegetative cells, respectively.We suggest that glutathione reductase plays a role in the protection mechanism which removes oxygen radicals in the N2-fixing cyanobacterium Nostoc muscorum.Abbreviations DTNB
5-5-dithiobis-(2-nitrobenzoic acid)
- EDTA
ethylenediaminetetra-acetic acid
- GR
glutathione reductase (EC1.6.4.2)
- GSH
reduced glutathione
- GSSG
oxidized glutathione
- OPT
O-phtaldialdehyde
- SOD
superoxide dismutase (EC 1.15.1.1) 相似文献
10.
The balance equations pertaining to the modelling of a slap-shaped bead containing immobilized enzyme uniformly distributed which catalyzes the sequential reactions of degradation of a polymeric substrate were written and analytically solved in dimensionless form. The effect of the Thiele modulus on the selectivity of consumption of each multimeric product was studied for a simple case. Whereas plain diffusional regime leads to lower selectivities than plain kinetic regime, improvements in selectivity of species A
i
relative to species Ai+1 may be obtained at the expense of higher Thiele moduli within a limited range when the diffusivity of A
i
is larger than that of A
i
+1, or when the pseudo first order kinetic constant describing the rate of consumption of A
i
is lower than that of Ai+1.List of Symbols
A
i
polymeric substrate containing i monomeric subunits
-
C
i
mol·m–3
normalized counterpart of C
i
-
C
i
mol·m–3
concentration of substrate A
i
-
C
i,0
mol·m–3
initial concentration of substrate A
i
-
C
i,0
normalized counterpart of C
i,0
-
D
ap,i
m2·s–1
apparent diffusivity of substrate A
i
-
k
i
s–1
pseudo-first order rate constant
-
K
m,i
mol·m–3
Michaelis-Menten constant associated with substrate A
i
-
L m
half-thickness of the catalyst slab
-
N
number of monomeric subunits of the largest substrate molecule
-
Th
Thiele modulus
-
V
i
mol·m–3·s–1
rate of rection of substrate A
i
- Vmax,i mol·m–3·s–1
maximum rate of reaction under saturating conditions of substrate A
i
-
x m
longitudinal coordinate
-
S
i,i+1
selectivity of enzyme with respect to substrates with consecutive numbers of monomeric subunits
Greek Symbols
i
ratio of maximum rates of reaction
-
i
ratio of apparent diffusivities 相似文献
11.
A. Gomez Aguirre R. Quintero A. Lopez-Munguia 《Bioprocess and biosystems engineering》1993,9(4):147-154
Enzyme reactors for the industrial hydrolysis of penicillin are analyzed in terms of biocatalyst stability to pH. A multicolumn system with packed beds placed in parallel and operating under recirculating conditions is proposed as an adequate reactor for this process. The system is studied both experimentally and with the aid of a simulation program.List of Symbols
A
transversal area (cm2)
-
C
A
ammonia concentration in the reaction mixture (M)
-
C
1
concentration of KH2PO4 in buffer (M)
-
C
2
concentration of K2HPO4 in buffer (M)
-
d
p
biocatalyst diameter (cm)
-
E
enzyme or biocatalyst concentration (gcat l–1)
-
K
APA
APA non competitive inhibition constant (M)
-
K
IS
excess substrate inhibition constant (M)
-
Km
constant Michaelis-Menten (M)
-
K
PAA
PAA competitive inhibition constant (M)
-
Q
recirculation flow rate (cm3 min–1)
-
Q
T
recirculation flow rate per column (cm3 min–1)
-
Re
Reynolds number
-
S
E
substrate concentration entering the neutralization tank (M)
-
S
0
initial substrate concentration (M)
-
S
T
substrate concentration in neutralization tank (M)
-
t
time (min)
-
v
i
initial reactor rate (mol min–1 gcat–1)
-
V
s
superficial velocity (cm seg–1)
-
V
T
volume of neutralization tank (cm3)
-
X
E
substrate conversion entering tank
-
X
T
substrate conversion in neutralization tank
-
X
conversion
-
Z
reactor length (cm)
-
z
axial position in reactor (cm)
-
z
*
non-dimensional axial position in reactor
-
biocatalyst's density (gcat cm–3)
-
p
pressure drop in the packed-bed reactor 相似文献
12.
Desulfotomaculum acetoxidans has been proposed to oxidize acetate to CO2 via an oxidative acetyl-CoA/carbon monoxide dehydrogenase pathway rather than via the citric acid cycle. We report here the presence of the enzyme activities required for the operation of the novel pathway. In cell extracts the following activities were found (values in brackets=specific activities and apparent K
m; 1 U·mg-1=1 mol·min-1·mg protein-1 at 37°C): Acetate kinase (6.3 U·mg-1; 2 mM acetate; 2.4 mM ATP); phosphate acetyltransferase (60 U·mg-1, 0.4 mM acetylphosphate; 0.1 mM CoA); carbon monoxide dehydrogenase (29 U·mg-1; 13% carbon monoxide; 1.3 mM methyl viologen); 5,10-methylenetetrahydrofolate reductase (3 U·mg-1, 0.06 mM CH3–FH4); methylenetetrahydrofolate dehydrogenase (3.6 U·mg-1, 0.9 mM NAD, 0.1 mM CH2=FH4); methenyltetrahydrofolate cyclohydrolase (0.3 U·mg-1); formyltetrahydrofolate synthetase (3 U·mg-1, 1.4 mM FH4, 0.4 mM ATP, 13 mM formate); and formate dehydrogenase (10 U·mg-1, 0.4 mM formate, 0.5 mM NAD). The specific activities are sufficient to account for the in vivo acetate oxidation rate of 0.26 U·mg-1.Non-standard abbreviations FH4
Tetrahydrofolate
- CHO-FH4
N10-formyltetrahydrofolate
- CHFH4
N5,N10-methenyltetrahydrofolate
- CH2=FH4
N5,N10-methylenetetrahydrofolate
- CH3–FH4
N5-methyltetrahydrofolate
- MOPS
morpholinopropane sulfonic acid
- DTT
d,l-1,4-dithiothreitol
- TRIS
tris-(hydroxymethyl)-aminomethane
- Ap5A
p1,P5-di(adenosine-5)pentaphosphate
- MV
methyl viologen 相似文献
13.
Rhodopseudomonas acidophila strain 7050 can satisfy all its nitrogen and carbon requirements from l-alanine. Addition of 100 M methionine sulfoximine to alanine grown cultures had no effect on growth rate indicating that deamination of alanine via alanine dehydrogenase and re-assimilation of the released NH
4
+
by glutamine synthetase/glutamate synthase was an insignificant route of nitrogen transfer in this bacterium. Determination of aminotransferase activities in cell-free extracts failed to demonstrate the presence of direct routes from alanine to either aspartate or glutamate. The only active aminotransferase involving l-alanine was the alanine-glyoxylate enzyme (114–167 nmol·min–1·mg–1 protein) which produced glycine as end-product. The amino group of glycine was further transaminated to yield aspartate via a glycineoxaloacetate aminotransferase (117–136 nmol·min–1 ·mg–1 protein). No activity was observed when 2-oxoglutarate was substituted for oxaloacetate. The formation of glutamate from aspartate was catalysed by aspartate-2-oxoglutarate aminotransferase (85–107 nmol·min–1·mg–1 protein). Determinations of free intracellular amino acid pools in alanine and alanine+100 M methionine sulfoximine grown cells showed the predominance of glutamate, glycine and aspartate, providing further evidence that in alanine grown cultures R. acidophila satisfies its nitrogen requirements for balanced growth by transamination.Abbreviations ADH
alanine dehydrogenase
- GDH
glutamate dehydrogenase
- GS
glutamine synthetase
- GOGAT
glutamate synthase
- MSO
methionine sulfoximine
- GOT
glutamate-oxaloacetate aminotransferase
- GPT
glutamate-pyruvate amino-transferase
- AGAT
alanine-glyoxylate aminotransferase
- GOAT
glycine-oxaloacetate aminotransferase
- GOTAT
glycine-2-oxoglutarate aminotransferase
- AOAT
alanine-oxaloacetate aminotransferase 相似文献
14.
A necessary condition is found for the intermediate temperatures and substrate concentrations in a series of CSTR's performing an enzyme-catalyzed reaction which leads to the minimum overall volume of the cascade for given initial and final temperatures and substrate concentrations. The reaction is assumed to occur in a single phase under steady state conditions. The common case of Michaelis-Menten kinetics coupled with first order deactivation of the enzyme is considered. This analysis shows that intermediate stream temperatures play as important a role as intermediate substrate concentrations when optimizing in the presence of nonisothermal conditions. The general procedure is applied to a practical example involving a series of two reactors with reasonable values for the relevant five operating parameters. These parameters are defined as dimensionless ratios involving activation energies (or enthalpy changes of reaction), preexponential factors, and initial temperature and substrate concentration. For negligible rate of deactivation, the qptimality condition corresponds to having the ratio of any two consecutive concentrations as a single-parameter increasing function of the previous ratio of consecutive concentrations.List of Symbols
C
E,0 mol.m–3
Initial concentration of active enzyme
-
C
E,i mol.m–3
Concentration of active enzyme at the outlet of the i-th reactor
-
C
S,0 mol.m–3
Initial concentration of substrate
-
C
S,i mol.m–3
Concentration of substrate at the outlet of the i-th reactor
-
Da
i
Damköhler number associated with the i-th reactor ((V
i.kv,0.CE,0)/(Q.CS,0))
-
Da
min
Minimum value of the overall Damköhler number
-
Da
tot
Overall Damköhler number
-
E
d J.mol–1
Activation energy of the step of deactivation of the enzyme
-
E
m J.mol–1
Standard enthalpy change of the step of binding of substrate to the enzyme
-
E
v J.mol–1
Activation energy of the step of enzymatic transformation of substrate
-
i
Integer variable
-
j
Dummy integer variable
-
k
Dummy integer variable
-
k
d,i s–1
Kinetic constant associated with the deactivation of enzyme in the i-th reactor (k
d,o·exp{–E
d/(R.T
i})
-
k
d,0 s–1
Preexponential factor of the kinetic constant associated with the deactivation of the enzyme
-
K
m,i mol.m–3
Equilibrium constant associated with the binding of substrate to the enzyme in the i-th reactor, (k
m,o·exp{–E
m}(R.T
i})
-
K
m,0 mol.m–3
Preexponential factor of the Michaelis-Menten constant associated with the binding of substrate to the enzyme
-
k
v,i s–1
Kinetic constant associated with the transformation of the substrate by the enzyme in the i-th reactor (k
v,o·exp{–E
v/(R.T
i}))
-
k
v,0 s–1
Preexponential factor of the kinetic constant associated with the transformation of the substrate by the enzyme
-
N
Number of reactors in the series
-
Q m3.s–1
Volumetric flow rate of reacting liquid through the reactor network
-
R J.K–1.mol–1
Ideal gas constant
-
T
i K
Absolute temperature at the outlet of the i-th reactor
-
T
0 K
Initial absolute temperature
-
V
i m3
Volume of the i-th reactor
-
v
max mol.m–3.s–1
Maximum rate of reaction under saturation conditions of substrate
-
x
i
Normalized concentration of substrate (CS,i/CS, 0)
-
x
i,opt
Optimum value of the normalized concentration of substrate
-
y
i
Dimensionless temperature (exp{–T
0/T
i})
-
y
i,opt
Optimum value of the dimensionless temperature
Greek Symbols
Dimensionless preexponential factor associated with the Michaelis-Menten constant (K
m,0/Cs,0)
-
Dimensionless activation energy of the step of enzymatic transformation of substrate (E
v/R.T0))
-
Dimensionless standard enthalpy change of the step of binding of substrate to the enzyme (E
m/(R.T0))
-
Dimensionless activation energy of the step of deactivation of the enzyme (E
d/(R.T0))
-
Dimensionless deactivation preexponential factor ((k
d,0.CS,0)/(kv,0.CE,0) 相似文献
15.
Summary Cellobiose oxidase from Phanerochaete chrysosporium was used for continuous monitoring of cellulase action on microcrystalline cellulose (Avicel). Two protocols are described, the parameter monitored being either the decline in electrode potential as ferricyanide is reduced or consumption of dioxygen. Most experiments used a commercial cellulase preparation from Trichoderma reesei and ferricyanide as acceptor. Within 1 min of an addition of cellulase, ferricyanide reduction reached a steady rate. This was converted into a rate of production of substrate for celobiose oxidase, in mol·min–1. Experiments were conducted either with a constant concentration of cellulase and increasing Avicel, or with constant Avicel and increasing cellulase. Kinetic analysis of the experiments with constant cellulase indicated a K
mof 4.8 ± 1.0 (g cellulose)·1–1, which was close to the value predicted from binding studies. The specific activity of the cellulase was measured as 375±25 mol·(g cellulase)–1·min–1 in experiments with a high cellulose concentration, but was less than half this value when the cellulose was saturated with cellulase. The maximal rate of cellulose degradation was 9.6±1.3 mol·(g cellulose)–1·min–1. 相似文献
16.
An NADP+ —dependent reversible 3-hydroxycarboxylate oxidoreductase present in Clostridium tyrobutyricum has been purified. As judged by gel electrophoresis the enzyme was pure after a 940-fold enrichment by four chromatographic steps. Its molecular mass was estimated to be 40–43 kDa. The enzyme was most active at pH 4.5 in the reduction of 3-oxobutyrate. Other substrates were 3-oxovalerate, 3-oxocaproate, 3-oxoisocaproate and 4-chloro-3-oxobutyrate. Except for the latter all substrates were converted enantioselectively to (S)-3-hydroxy acids in the presence of NADPH. 4-Chloro-3-oxobutyrate was reduced to the (R)-3-hydroxy acid. The specific activity of the enzyme was about 1400 mol min–1 mg–1 protein for the reduction of 3-oxobutyrate at pH 5.0. The Michaelis constant (K
m) values for 3-oxobutyrate, 3-oxovalerate and 3-oxocaproate were determined to be 0.22, 1.6 and 3.0 mM, respectively. The K
m values for dehydrogenation of (S)-3-hydroxybutyrate, (S)-3-hydroxyvalerate and (S)-3-hydroxycaproate were found to be 2.6, 1.1 and 5.2 mM, respectively. The identity of 43 of the first 45 N-terminal amino acid residues has been determined. So far such enzyme activities have been described in eucaryotes only.Dedicated to Prof. A. Trebst on the occasion of his 65th birthday 相似文献
17.
Alberto Concu Claudio Marcello 《European journal of applied physiology and occupational physiology》1993,66(1):11-17
Using the impedance cardiography method, heart rate (
c) matched changes on indexed stroke volume (SI) and cardiac output (CI) were compared in subjects engaged in different types of training. The subjects consisted of untrained controls (C), volleyball players (VB) who spent about half of their training time (360 min · week–1) doing anaerobic conditioning exercises and who had a maximal oxygen uptake (
) 41% higher than the controls, and distance runners (D) who spent all their training time (366 min·week–1) doing aerobic conditioning exercises and who had a
26% higher than VB. The subjects performed progressive submaximal cycle ergometer exercise (10 W·min–1) up to
c of 150 beats·min–1. In group C, SI had increased significantly (P<0.05) at
c of 90 beats·min–1 ( + 32%) and maintained this difference up to 110 beats·min–1, only to return to resting values on reaching 130 beats·min–1 with no further changes. In group VB, SI peaked (+ 54%) at
c of 110 beats·min–1, reaching a value significantly higher than that of group C, but decreased progressively to 22010 of the resting value on reaching 150 beats·min–1. In group D, SI peaked at
c of 130 beats·min–1 (+ 54%), reaching a value significantly higher than that of group VB, and showed no significant reduction with respect to this peak value on reaching 150 beats·min–1. As a consequence, the mean CI increase per
c unit was progressively higher in VB than in C (+46%) and in D than in VB (+ 105%). It was concluded that thef
c value at which SI ceased to increase during incremental exercise was closely related to the endurance component in the training programme. 相似文献
18.
A. K. McConnell E. S. G. Semple C. T. M. Davies 《European journal of applied physiology and occupational physiology》1993,66(4):332-337
The present investigation examined the relationship between CO2 sensitivity [at rest (S
R) and during exercise (S
E)] and the ventilatory response to exercise in ten elderly (61–79 years) and ten younger (17–26 years) subjects. The gradient of the relationship between minute ventilation and CO2 production (
E/
CO2) of the elderly subjects was greater than that of the younger subjects [mean (SEM); 32.8 (1.6) vs 27.3 (0.4); P<0.01]. At rest, S
R was lower for the elderly than for the younger group [10.77 (1.72) vs 16.95 (2.13) 1 · min–1 · kPa–1; 1.44 (0.23) vs 2.26 (0.28) 1 · min–1 · mmHg–1; P<0.05], but S
E was not significantly different between the two groups [17.85 (2.49) vs 19.17 (1.62) l · min–1 · kPa–1; 2.38 (0.33) vs 2.56 (0.21) 1 · min–1 · mmHg–1]. There were significant correlations between both S
R and S
E, and
E/
CO2 (P<0.05; P<0.001) for the younger group, bot none for the elderly. The absence of a correlation for the elderly supports the suggestion that
E/
CO2 is not an appropriate index of the ventilatory response to exercise for elderly humans. 相似文献
19.
F. X. Malcata 《Bioprocess and biosystems engineering》1995,13(1):51-55
The balance equations pertaining to the modelling of a CSTR performing an enzyme-catalyzed reaction in the presence of enzyme deactivation are developed. Combination of heuristic correlations for the size-dependent cost of equipment and the purification-dependent cost of recovery of product with the mass balances was used as a basis for the development of expressions relating a (suitably defined) dimensionless economic parameter with the optimal outlet substrate concentration under the assumption that overall production costs per unit mass of product were to be minimized. The situation of Michaelis-Menten kinetics for the substrate depletion and first order kinetics for the deactivation of enzyme (considering that the free enzyme and the enzyme in the enzyme/substrate complex deactivate at different rates) was explored, and plots for several values of the parameters germane to the analysis are included.List of Symbols
C
E
mol m–3
concentration of active enzyme
-
C
E,0
mol m–3
initial concentration of active enzyme
-
C
p
mol m–3
concentration of product of interest
-
C
s
mol m–3
concentration of substrate
-
C
s,0
mol m–3
initial concentration of substrate
-
I $
capital cost of equipment
-
k
d
s–1
deactivation constant of free enzyme
-
k
d
s–1
deactivation constant of enzyme in enzyme/substrate complex
-
K
m
mol m–3
Michaelis-Menten constant
-
K
m
dimensionless counterpart of K
m
-
k
r
s–1
rate constant associated with conversion of enzyme/substrate complex into product
-
M
w
kg mol–1
molecular weight of product of interest
-
P $ kg–1
cost of recovery of product of interest in pure form
-
Q m3s–1
volumetric flow rate
-
V m3
volume of reactor
-
X $ kg–1
global manufacture cost of product of interest in pure form
-
X
dimensionless counterpart of X
Greek Symbols
1 $ m–1.8
constant
-
2 $ m–3
constant
-
t s
useful life of CSTR
-
0
ratio of initial concentrations of enzyme and substrate
-
ratio of deactivation constant of free enzyme to rate constant of depletion of substrate
-
ratio of deactivation constants
-
univariate function expressing the dependence of the rate of enzyme deactivation on C
S
-
univariate function expressing the dependence of the rate of substrate depletion on C
S
-
dimensionless economic parameter 相似文献
20.
S. N. Mukhopadhyay A. Ornelas Vale E. Camargo Rubio G. Cassarubias Arcos 《Applied microbiology and biotechnology》1978,6(1):55-66
Summary Submerged batch cultivation under controlled environmental conditions of pH 3.8, temperature 30°C, and KLa200 h–1 (above 180 mMO2
l
–1 h–1 oxygen supply rate) produced a maximum (12.0 g·l
–1) SCP (Candida utilis) yield on the deseeded nopal fruit juice medium containing C/N ratio of 7.0 (initial sugar concentration 25 g·l
–1) with a yield coefficient of 0.52 g cells/g sugar. In continuous cultivation, 19.9 g·l
–1 cell mass could be obtained at a dilution rate (D) of 0.36 h–1 under identical environmental conditions, showing a productivity of 7.2 g·l
–1·h–1. This corresponded to a gain of 9.0 in productivity in continuous culture over batch culture. Starting with steady state values of state variables, cell mass (CX–19.9 g·l
–1), limiting nutrient concentration (Cln–2.5 g·l
–1) and sugar concentration (CS–1.5 g·l
–1) at control variable conditions of pH 3.8, 30°C, and KLa 200 h–1 keeping D=0.36 h–1 as reference, transient response studies by step changes of these control variables also showed that this pH, temperature and KLa conditions are most suitable for SCP cultivation on nopal fruit juice. Kinetic equations obtained from experimental data were analysed and kinetic parameters determined graphically. Results of SCP production from nopal fruit juice are described.Nomenclature Cln
concentration of ammonium sulfate (g·l
–1)
- CS
concentration of total sugar (g·l
–1)
- CX
cell concentration (g·l
–1)
- D
dilution rate (h–1)
- Kln
Monod's constant (g·l
–1)
- m
maintenance coefficient (g ammonium sulfate cell–1 h–1)
- m(S)
maintenance coefficient (g sugar g cell–1 h–1)
- t
time, h
- Y
yield coefficient (g cells/g ammonium sulfate)
- Ym
maximum of Y
- YS
yield coefficient based on sugar consumed (g cells · g sugar–1)
- YS(m)
maximum value of YS
-
µm
maximum specific growth rate constant (h–1) 相似文献