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1.
Culture of human hepatocytes from small surgical liver biopsies. Biochemical characterization and comparison with in vivo 总被引:4,自引:0,他引:4
M. José Gómez-Lechón Pilar López Teresa Donato Angel Montoya Amparo Larrauri Patricia Giménez Ramón Trullenque Ricardo Fabra José V. Castell 《In vitro cellular & developmental biology. Plant》1990,26(1):67-74
Summary High yields of human hepatocytes (up to 23×106 viable cells/g) were obtained from small surgical liver biopsies (1 to 3 g) by a two-step collagenase microperfusion method.
Cell viability was about 95%, attachment efficiency of hepatocytes seeded on fibronectin-coated plates was 80% within 1 h
after plating, and cells survived for about 2 wk in serum-free Ham’s F12 containing 0.2% bovine serum albumin, 10−8
M insulin, and 10−8
M dexamethasone. To evaluate the metabolism of human hepatocytes in serum-free conditions, we measured their most characteristic
biochemical functions and compared them to those reported for human liver. After 24 h in culture, glycogen content was 1250±177
nmol glucose/mg cell protein and remained stable for several days. Gluconeogenesis from lactate in hormone-free media was
(3.50±0.17 nmol glucose·mg−1·min−1) similar to that reported for human liver. Insulin at 10−8
M activated glycolysis (×1.40) and glycogenesis (×1.34), and glucagon at 10−9
M stimulated gluconeogenesis (×1.35) and glycogenolysis (×2.18). Human hepatocytes synthesized albumin, transferrin, fibrinogen,
α1-antitrypsin, α1-antichymotrypsin, α1-acid glycoprotein, haptoglobin, α2-macroglobulin, and plasma fibronectin and excreted them to the culture medium. Maximum protein synthesis was stimulated by
10−9
M dexamethasone. Basal urea synthesis oscillated between 2.5 and 3.5 nmol·mg−1 cell protein·min−1, about 5 times the value estimated for human liver. Cytochrome P-450 decreased in culture but it was still 20% of freshly
isolated hepatocytes by Day 5 in culture. In addition, ethoxycumarin-O-deethylase and aryl hydrocarbon hydroxylase could be
induced in vitro by treatment with methyl cholanthrene. Glutathione levels were similar to those reported for human liver
(35 nmol·mg−1).
The results of our work show that adult human hepatocytes obtained from small surgical biopsies and cultured in chemically
defined conditions express their most important metabolic functions to an extent that is similar to that reported for adult
human liver. 相似文献
2.
Moro D Bradshaw SD 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(8):538-548
A laboratory study investigated the metabolic physiology, and response to variable periods of water and sodium supply, of
two arid-zone rodents, the house mouse (Mus domesticus) and the Lakeland Downs short-tailed mouse (Leggadina lakedownensis) under controlled conditions. Fractional water fluxes for M. domesticus (24 ± 0.8%) were significantly higher than those of L. lakedownensis (17 ± 0.7%) when provided with food ad libitum. In addition, the amount of water produced by M. domesticus and by L. lakedownensis from metabolic processes (1.3 ± 0.4 ml · day−1 and 1.2 ± 0.4 ml · day−1, respectively) was insufficient to provide them with their minimum water requirement (1.4 ± 0.2 ml · day−1 and 2.0 ± 0.3 ml · day−1, respectively). For both species of rodent, evaporative water loss was lowest at 25 °C, but remained significantly higher
in M. domesticus (1.1 ± 0.1 mg H2O · g−0.122 · h−1) than in L. lakedownensis (0.6 ± 0.1 mg H2O · g−0.122 · h−1). When deprived of drinking water, mice of both species initially lost body mass, but regained it within 18 days following
an increase in the amount of seed consumed. Both species were capable of drinking water of variable saline concentrations
up to 1 mol · l−1, and compensated for the increased sodium in the water by excreting more urine to remove the sodium. Basal metabolic rate
was significantly higher in M. domesticus (3.3 ± 0.2 mg O2 · g−0.75 · h−1) than in L. lakedownensis (2.5 ± 0.1 mg O2 · g−0.75 · h−1). The study provides good evidence that water flux differences between M. domesticus and L. lakedownensis in the field are due to a requirement for more water in M. domesticus to meet their physiological and metabolic demands. Sodium fluxes were lower than those observed in free-ranging mice, whose
relatively high sodium fluxes may reflect sodium associated with available food.
Accepted: 16 August 1999 相似文献
3.
A comparative study of the development of uptake hydrogenase and nitrogenase activities in cells of the cyanobacterium Anabaena variabilis was performed.
The induction of heterocysts is followed by the induction of both in vivo hydrogen uptake and nitrogenase activities. Interestingly,
a low but significant H2-uptake [2–7 μmoles of H2 · mg−1 (Chl a) · h−1] occurs in cultures with no heterocysts and with no nitrogenase activity. A slight stimulatory effect (30–40%) of H2 on in vivo H2-uptake was observed during the early stages of nitrogenase induction.
However, exogenous H2 does not further stimulate the induction of in vivo hydrogen uptake observed during heterocyst differentiation. Similarly,
organic carbon (fructose) did not influence the induction of either in vivo hydrogen uptake or nitrogenase activities. Exogenous
fructose supports higher in vivo hydrogen uptake and nitrogenase activities when the cells enter late exponential phase of
growth.
Received: 22 November 1995 / Accepted: 22 December 1995 相似文献
4.
Collopy-Junior I Kneipp LF da Silva FC Rodrigues ML Alviano CS Meyer-Fernandes JR 《Archives of microbiology》2006,185(5):355-362
In this work, we characterized an ecto-ATPase activity in intact mycelial forms of Fonsecaea pedrosoi, the primary causative agent of chromoblastomycosis. In the presence of 1 mM EDTA, fungal cells hydrolyzed adenosine-5′-triphosphate (ATP) at a rate of 84.6 ± 11.3 nmol Pi h−1 mg−1 mycelial dry weight. The ecto-ATPase activity was increased at about five times (498.3 ± 27.6 nmol Pi h−1 mg−1) in the presence of 5 mM MgCl2, with values of V
max and apparent K
m for Mg-ATP2−corresponding to 541.9 ± 48.6 nmol Pi h−1 mg−1 cellular dry weight and 1.9 ± 0.2 mM, respectively. The Mg2+-stimulated ecto-ATPase activity was insensitive to inhibitors of intracellular ATPases such as vanadate (P-ATPases), bafilomycin A1 (V-ATPases), and oligomycin (F-ATPases). Inhibitors of acid phosphatases (molybdate, vanadate, and fluoride) or alkaline phosphatases (levamizole) had no effect on the ecto-ATPase activity. The surface of the Mg2+-stimulated ATPase in F. pedrosoi was confirmed by assays in which 4,4′-diisothiocyanostylbene-2,2′-disulfonic acid (DIDS), a membrane impermeant inhibitor, and suramin, an inhibitor of ecto-ATPase and antagonist of P2 purinoreceptors. Based on the differential expression of ecto-ATPases in the different morphological stages of F. pedrosoi, the putative role of this enzyme in fungal biology is discussed. 相似文献
5.
Nigel J. Adams Berry Pinshow Leonard Z. Gannes 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(6):444-450
We used tritium-labeled water to measure total body water, water influx (which approximated oxidative water production) and
water efflux in free-flying tippler pigeons (Columba livia) during flights that lasted on average 4.2 h. At experimental air temperatures ranging from 18 to 27 °C, mean water efflux
by evaporation and excretion [6.3 ± 1.3 (SD) ml · h−1, n = 14] exceeded water influx from oxidative water and inspired air (1.4 ± 0.7 ml · h−1, n = 14), and the birds dehydrated at 4.9 ± 0.9 ml · h−1. This was not significantly different from gravimetrically measured mass loss of 6.2 ± 2.1 g · h−1 (t = 1.902, n = 14, P>0.05). This flight-induced dehydration resulted in an increase in plasma osmolality of 4.3 ± 3.0 mosmol · kg−1 · h−1 during flights of 3–4 h. At 27 °C, the increase in plasma osmolality above pre-flight levels (ΔP
osm = 7.6±4.29 mosmol · kg−1 · h−1, n = 6) was significantly higher than that at 18 °C (ΔP
osm = 0.83±2.23 mosmol · kg−1 · h−1, (t = 3.43, n = 6, P < 0.05). Post-flight haematocrit values were on average 1.1% lower than pre-flight levels, suggesting plasma expansion. Water
efflux values during free flight were within 9% of those in the one published field study (Gessaman et al. 1991), and within
the range of values for net water loss determined from mass balance during wind tunnel experiments (Biesel and Nachtigall
1987). Our net water loss rates were substantially higher than those estimated by a simulation model (Carmi et al. 1992) suggesting
some re-evaluation of the model assumptions is required.
Accepted: 8 April 1997 相似文献
6.
Jesús Adolfo Jiménez Nieves Alonso-Blázquez Dolores López-Vela Cristina Celestino Mariano Toribio Jesus Alegre 《In vitro cellular & developmental biology. Plant》2011,47(5):578-588
Somatic embryogenesis can be induced in the leaves of cork oak (Quercus suber L.) trees. The use of this propagation system in multivarietal forestry requires the mass production of cloned plants at
low cost. Investigations were made into the influence of three types of Erlenmeyer flask and three orbiting speeds (60, 110,
and 160 rpm) on oxygen transfer rate (KL
a), the shear force index (SFI), biomass production, and the proliferation of embryogenic clumps (EMCs) in cultures during
the proliferation phase. KL
a varied between 0.11 and 1.47 h−1 without biomass production being limited by oxygen availability. The EMCs grew even in hypoxic conditions, although the suppression
of gaseous exchange strongly reduced biomass production. Cultures with different levels of hydrodynamic stress and SFI values
(1.4·10−3–8.8·10−3 cm min−1) were obtained. Proliferation rates of EMCs increased with agitation rate and the SFI. The largest number of EMCs was obtained
in baffled flasks agitated at 160 rpm (KL
a of 1.47 h−1, and SFI of 8.8·10−3 cm min−1) with mild hydrodynamic stress enhancing growth. Biomass production increased with agitation and hydrodynamic stress, but
only when the SFI value was below 5·10−3 cm min−1. The greatest biomass production was obtained in smooth 100 ml flasks agitated at 160 rpm. The differentiation of embryos
was favoured by the lowest KL
a (0.11 h−1) and SFI (1.40·103 cm min−1) values, achieved using these flasks when agitated at 60 rpm. 相似文献
7.
Bernd Schröder Ina Rittmann Ernst Pfeffer Gerhard Breves 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):43-51
Unidirectional flux rates of Ca2+ across gastrointestinal tissues from sheep and goats were measured in vitro by applying the Ussing-chamber technique. Except for the sheep duodenum, mucosal to serosal Ca2+ flux rates (J
ms) exceeded respective flux rates in the opposite direction (J
sm) in both species and in all segments of the intestinal tract. This resulted in net Ca2+ flux rates␣(J
net = J
ms − J
sm) ranging between −2 and 9 nmol · cm−2 · h−1 in sheep and between 10 and 15 nmol cm−2 · h−1 in goats. In sheep, only J
net in jejunum, and in goats, J
netin duodenum and jejunum were significantly different from zero. Using sheep rumen wall epithelia, significant J
net of Ca2+ of around 5 nmol · cm−2 · h−1 could be detected. Since the experiments were carried out in the absence of an electrochemical gradient, significant net
Ca2+ absorption clearly indicates the presence of active mechanisms for Ca2+ transport. Dietary Ca depletion caused increased calcitriol plasma concentrations and induced significant stimulations of
net Ca2+ absorption in goat rumen. J
net of Ca2+ across goat rumen epithelia was significantly reduced by 1 mmol · l −1 verapamil in the mucosal buffer solution. In conclusion, there is clear evidence for the rumen as a main site for active
Ca2+ absorption in small ruminants. Stimulation of active Ca2+ absorption by increased plasma calcitriol levels and inhibition by mucosal verapamil suggest mechanistic and regulatory similarities
to active Ca2+ transport as described for the upper small intestines of monogastric species.
Accepted: 31 July 1996 相似文献
8.
Submerged aquatic higher plants maintain acropetal water transport to the young leaves in active growth to satisfy their
demand for nutrients and hormones derived from the roots. We here present the first measurements of hydraulic properties for
a submerged plant, the monocotyledon Sparganium emersum Rehman. The hydraulic conductance per unit length, Kh, was measured in leaf segments without the leaf tip and shown to be greater in old, fully developed leaves (1.5 · 10−10 · m4 · MPa−1 · s−1) than in young leaves (1.0 · 10−10 · m4 · MPa−1 · s−1). In leaves with intact leaf tips, however, Kh was significantly greater in the youngest leaves, which suggests that the leaf tip with the hydathode influences resistance
and thus flow. Microscopy confirmed that the hydathodal area, which is an apical opening, undergoes structural changes with
leaf age; a matrix of microorganisms develops in the older leaves and probably restricts water flow by clogging the hydathodes.
The leaf specific conductivity expressing transport capacity relative to the leaf area supplied, of S. emersum (0.1 · 10−8 to 9 · 10−8 · m2 MPa−1· s−1) was within the same range as for various species of terrestrial ferns, vines and trees. This finding does not support the
traditional concept of functionally reduced vascular transport in
Received: 15 July 1996 / Accepted: 30 November 1996 相似文献
9.
Pre-matured florets of Benibana, a cultivar of saffron thistle (Carthamus tinctorius L.) was irradiated with UV-B (280–320 nm) or UV-C (254 nm) light for 48 h at 23±1 °C and the influence of UV-light on carthamin
accumulation and floret elongation was investigated. UV-C light enhances carthamin accumulation most prominently, showing
a specific value of 52.3 nmol carthamin·dm−3·h−1·25μm−2 (13.9 times of control), while it restricts floret elongation by a light-suppression manner (net elongation: 0.058 mm·h−1, one ninth of control). UV-B light is also promotive for the red colour appearance (25.0 nmol carthamin·dm−3·h−1·25 μm−2, 6.7 times of control) with suppressing floret elongation (net elongation: 0.17 mm·h−1, one third of control). Heterogeneous productivity of carthamin was seen in floret tissues after continuous treating under
UV-C light. Carthamin accumulation, heterogeneous carthamin productivity and decrease of floret elongation restraint under
UV-lights are discussed. 相似文献
10.
Bacillus mycoides strain RIJ B-017, a growth-associated poly-3-hydroxybutyrate (PHB) producer was grown on sucrose-containing media. PHB accumulated
in cells up to 72% of dry cell mass. The overall maximum value of PHB yield (Y
p/s) and productivities (Q
p andq
p) 250 mgp/gs, 120 mgp L−1 h−1 and 30 mgp gx
−1 h−1, respectively, were obtained at 15 g/L sucrose. Differential scanning calorimeter heating curve showed two peaks, one at
95.9 °C and another at 165.4°C with a shoulder around 154.6 °C. The viscosity-average molar mass in chloroform at 27°C was
505 kDa. The carbon content of PHB was 55.4% of the mass. 相似文献
11.
S A Shaikh J M Khire M I Khan 《Journal of industrial microbiology & biotechnology》1997,19(4):239-245
A thermostable β-galactosidase was produced extracellularly by a thermophilic Rhizomucor sp, with maximum enzyme activity (0.21 U mg−1) after 4 days under submerged fermentation condition (SmF). Solid state fermentation (SSF) resulted in a nine-fold increase
in enzyme activity (2.04 U mg−1). The temperature range for production of the enzyme was 38–55°C with maximum activity at 45°C. The optimum pH and temperature
for the partially purified enzyme was 4.5 and 60°C, respectively. The enzyme retained its original activity on incubation
at 60°C up to 1 h. Divalent cations like Co2+, Mn2+, Fe2+ and Zn2+ had strong inhibitory effects on the enzyme activity. The K
m and V
max for p-nitrophenyl-β- D-galactopyranoside and o-nitrophenyl-β - D-galactopyranoside were 0.39 mM, 0.785 mM and 232.1 mmol min−1 mg−1 respectively. The K
m and V
max for the natural substrate lactose were 66.66 μM and 0.20 μ mol min−1 mg−1.
Received 10 March 1997/ Accepted in revised form 17 July 1997 相似文献
12.
Two carotenoid 1,2-hydratase (CrtC) genes from the photosynthetic bacteria Rubrivivax gelatinosus and Thiocapsa roseopersicina were cloned and expressed in Escherichia coli in an active form and purified by affinity chromatography. The biochemical properties of the recombinant enzymes and their
substrate specificities were studied. The purified CrtCs catalyze cofactor independently the conversion of lycopene to 1-HO-
and 1,1′-(HO)2-lycopene. The optimal pH and temperature for hydratase activity was 8.0 and 30°C, respectively. The apparent K
m and V
max values obtained for the hydration of lycopene were 24 μM and 0.31 nmol h−1 mg−1 for RgCrtC and 9.5 μM and 0.15 nmol h−1 mg−1 for TrCrtC, respectively. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis revealed two protein bands of 44 and
38 kDa for TrCrtC, which indicate protein processing. Both hydratases are also able to convert the unnatural substrate geranylgeraniol
(C20 substrate), which functionally resembles the natural substrate lycopene. 相似文献
13.
Hee Wook Ryu So Jong Kim Kyung-Suk Cho Tae Ho Lee 《Biotechnology and Bioprocess Engineering》2008,13(3):360-365
In the present study, toluene elimination in the polyurethane (PU) biofilter during long-term (145 day) operation was characterized,
and assessed the effects of changing the inlet loading and space velocity (SV). A very high elimination capacity of 3.7 kg·m−3·h−1 was obtained at an inlet loading of 4.0 kg·m–3·h−1 (inlet toluene concentration of 900 ppmv at a SV of 1,040 h−1). Backwashing with irrigation and compressed air allowed maintenance of a pressure drop of < 80 mm H2O·m−1-filter at an SV of 830 h−1 and an elimination efficiency of > 90% during the 145 day of operation. In conclusion, the PU biofilter can overcome the
problems of clogging caused by excess biomass growth and of low treatment capacities of conventional biofilters. 相似文献
14.
Schröder B Vössing S Breves G 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(7):487-494
From various in vivo and in vitro studies it has been shown that the rumen represents a significant site of Ca2+ absorption in sheep and goats. It was the aim of the present study to further characterize the underlying mechanisms. Unidirectional
flux rates of Ca2+ across rumen wall epithelia of sheep were measured in vitro by applying the Ussing-chamber technique in the absence of electrochemical
gradients. Under these conditions, significant Ca2+ net flux rates (Jnet) clearly indicate the presence of active mechanisms for Ca2+ transport. Short chain fatty acids (SCFAs) caused highest stimulation of Ca2+ Jnet (6.3 ± 1.9 nmol · cm−2 · h−1) when used as a mixture of acetate, proprionate and butyrate in physiological proportions (36, 15, 9 mmol · l−1, respectively). The effect of 30 mmol · l−1 butyrate (3.2 ± 0.6 nmol · cm−2 · h−1) was higher than respective amounts of propionate and acetate (0.6 ± 0.8 nmol · cm−2 · h−1 and 0.9 ± 0.8 nmol · cm−2 · h−1, respectively). Eliminating SCFAs resulted in Ca2+ Jnet of 0.4 ± 1.1 nmol . cm−2 . h−1. Addition of Ca channel blocker verapamil (mucosal 1 mmol · l−1) had no significant effect on SCFA-stimulated Jnet of Ca2+, whereas application of Na+/H+ inhibitor amiloride (mucosal 1 mmol · l−1) further enhanced the Ca2+ Jnet by >65%. The Ca2+-pump inhibitor vanadate had no significant effect on Jnet of Ca2+. Dietary Ca depletion enhanced calcitriol plasma concentrations but had no effect on active Ca2+ absorption across the rumen wall of sheep. In addition, no effect on active Ca2+ absorption could be observed during early lactation. In conclusion, there is clear evidence for the rumen as a main site
for active Ca2+ absorption in sheep. Our results suggest the presence of a Ca2+/H+ exchange mechanism in the apical membrane of rumen epithelial cells which depends on SCFA absorption and which does not seem
to be under the control of calcitriol. Basolateral Ca2+ extrusion occurs independently from Ca2+-pump activity and may be accomplished via Na+/Ca2+ exchange.
Accepted: 29 June 1999 相似文献
15.
Sharma NN Sharma M Bhalla TC 《Journal of industrial microbiology & biotechnology》2011,38(9):1235-1243
Nitrilase of Nocardia globerula NHB-2 was induced by short-chain aliphatic nitriles (valeronitrile > isobutyronitrile > butyronitrile > propionitrile) and
exhibited activity towards aromatic nitriles (benzonitrile > 3-cyanopyridine > 4-cyanopyridine > m-tolunitrile > p-tolunitrile). Hyperinduction of nitrilase (6.67 U mgDCW−1, 18.7 U mL−1) was achieved in short incubation time (30 h, 30°C) through multiple feeding of isobutyronitrile in the growth medium. The
nitrilase of this organism exhibits both substrate and product inhibition effects. In a fed batch reaction at 1 L scale using
hyperinduced resting cells corresponding to 10 U mL−1 nitrilase activity (1.5 mgDCW mL−1), a total of 123.11 g nicotinic acid was produced at a rate of 24 g h−1 gDCW−1. 相似文献
16.
Chaoning Liang Yanfen Xue Marco Fioroni Francisco Rodríguez-Ropero Cheng Zhou Ulrich Schwaneberg Yanhe Ma 《Applied microbiology and biotechnology》2011,89(2):315-326
A β-1,4-endoglucanase (Cel5A) was cloned from the genomic DNA of saccharolytic thermophilic eubacterium Thermoanaerobacter tengcongensis MB4 and functionally expressed in Escherichia coli. Substrate specificity analysis revealed that Cel5A cleaves specifically the β-1,4-glycosidic linkage in cellulose with high
activity (294 U mg−1; carboxymethyl cellulose sodium (CMC)). On CMC, kinetics of Cel5A was determined (K
m 1.39 ± 0.12 g l−1; k
cat/K
m 1.41 ± 0.13 g−1 s−1). Cel5A displays an activity optimum between 75 and 80 °C. Residues Glu187 and Glu289 were identified as key catalytic amino
acids by sequence alignment. Interestingly, derived from a non-halophilic bacterium, Cel5A exhibits high residual activities
in molar concentration of NaCl (3 M, 49.3%) and KCl (4 M, 48.6%). In 1 M NaCl, 82% of Cel5A activity is retained after 24
h incubation. Molecular Dynamics studies performed at 0 and 3 M NaCl, correlate the Cel5A stability to the formation of R-COO−···Na+ ···−OOC-R salt bridges within the Cel5A tertiary structure, while activity possibly relates to the number of Na+ ions trapped into the negatively charged active site, involving a competition mechanism between substrate and Na+. Additionally, Cel5A is remarkably resistant in ionic liquids 1-butyl-3-methyllimidazolium chloride (1 M, 54.4%) and 1-allyl-3-methylimidazolium
chloride (1 M, 65.1%) which are promising solvents for cellulose degradation and making Cel5A an attractive candidate for
industrial applications. 相似文献
17.
Summary Cells ofCandida shehatae repressed by growth in glucose- or D-xylose-medium produced a facilitated diffusion system that transported glucose (K
s±2 mM,V
max±2.3 mmoles g−1 h−1),d-xylose (K
s±125 mM,V
max±22.5 mmoles g−1 h−1) and D-mannose, but neither D-galactose norl-arabinose.
Cells derepressed by starvation formed several sugar-proton symports. One proton symport accumulated 3-0-methylglucose about
400-fold and transported glucose (K
s±0.12 mM,V
max ± 3.2 mmoles g−1 h−1) andd-mannose, a second proton symport transportedd-xylose (K
s± 1.0 mM,V
max 1.4 mmoles g−1 h−1) andd-galactose, whilel-arabinose apparently used a third proton symport. The stoicheiometry was one proton for each molecule of glucose or D-xylose
transported. Substrates of one sugar proton symport inhibited non-competitively the transport of substrates of the other symports.
Starvation, while inducing the sugar-proton symports, silenced the facilitated diffusion system with respect to glucose transport
but not with respect to the transport of D-xylose, facilitated diffusion functioning simultaneously with thed-xylose-proton symport. 相似文献
18.
Ferdinand Schanz 《Hydrobiologia》1986,134(2):183-192
Spectral light attenuation, from the surface to 20 m, was followed on 15 sunny days and compared with the vertical phytoplankton
distribution. The most penetrating wavelengths lie between 565 and 590 nm. High phytoplankton density causes a rapid loss
of blue light with depth. Consequently the yellow and red regions of the spectrum contain a relatively high proportion of
the light energy present at a particular depth. The vertical attenuation coefficients of monochromatic light Kd(λ) in the 400 to 700 nm region are influenced significantly by the phytoplankton biomass. The specific light attenuation
coefficient for chlorophyll a (kc) is highest below 550 nm (e.g. 450 nm, surface layer: kc = 0.027 m2 · mg−1, n = 14; lowermost layer: kc = 0.044 m2 · mg−1, n = 9). 相似文献
19.
Isochorismate hydroxymutase (i.e. isochorismate synthase, EC 5.4.99.6) was purified from an anthraquinone-producing cell-suspension
culture of Galium mollugo L. Although attempts to stabilize the labile enzyme met with little success, a substantial increase in enzyme activity was
observed in the presence of glycine betaine (500 mM). Column chromatography on solid supports other than diethylaminoethyl
(DEAE)-Sephacel, Phenylsepharose Cl-4B or Cibacron Blue 3G-A did not give active enzyme preparations. In spite of these drawbacks
the enzyme was purified 573-fold. Enzyme activity depended strictly on the presence of Mg2+. Kinetic data for chorismate in the forward reaction (K
m = 807 μM, V
max = 6.2 pkat · mg−1) and for isochorismate in the reverse reaction (K
m = 675 μM, V
max = 5.9 pkat · mg−1) were determined.
Received: 18 November 1996 / Accepted: 28 December 1996 相似文献
20.
I. C. Potter D. J. Macey A. R. Roberts P. C. Withers 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,166(5):331-336
When covered by moistened lint-free gauze, the larvae (ammocoetes) of the lamprey Geotria australis survived, without apparent discomfort, for 4 days in water-saturated air at 10, 15 and 20 °C. In air, the mean standard rates
of O2 consumption of medium to large ammocoetes of G. australis (xˉ=0.52 g) at 10, 15 and 20 °C were 14.5, 35.7 and 52.1 μl⋅g-1⋅h-1, respectively. At 15 °C, the slope of the relationship between log O2 consumption (μl O2⋅h-1) and log body weight for ammocoetes over a wide range in body weight was 0.987. The Q
10s for rate of O2 consumption between 10 and 15 °C, 15 and 20 °C and 10 and 20 °C were 4.9, 2.9 and 3.6, respectively. Our results and observations
of the ammocoetes suggest that, when out of water, larval G. australis derives most of its O2 requirements from cutaneous respiration, particularly at lower temperatures. This would be facilitated by the small size
and elongate shape (and thus a relatively high surface-to-volume ratio), low metabolic rate, thin dermis, extensive subdermal
capillary network and high haemoglobin concentration of larval G. australis.
Accepted: 28 March 1996 相似文献