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1.
Carmen Lapadatescu Christian Giniès Aleth Djian Henry-Eric Spinnler Jean-Luc Le Quéré Pascal Bonnarme 《Archives of microbiology》1999,171(3):151-158
The white-rot basidiomycete Bjerkandera adusta was cultivated in a liquid medium enriched with l-phenylalanine and various phospholipid sources (lecithin, egg yolk and asolectin). Three aromatic metabolites (benzaldehyde,
benzyl alcohol and benzoic acid) were produced under these culture conditions. High concentrations of benzaldehyde (404 mg
l–1) were obtained when the cultures were supplemented with 10 g lecithin l–1. Benzyl alcohol production was promoted when the strain was grown with 5 or 10 g lecithin l–1. In the absence of or with a low concentration of lecithin (2.5 g l–1), benzoic acid was the major aryl metabolite synthesized. The results presented here indicate that aryl alcohol oxidase,
an extracellular enzyme catalyzing the oxidation of benzyl alcohol into benzaldehyde, was maximally detected when significant
amounts of benzaldehyde were produced. Aryl alcohol oxidase activity was significantly enhanced in the presence of elevated
concentrations of phospholipid sources. Together with lignin peroxidase, methoxylated and hydroxylated aryl metabolites were
also synthesized under these culture conditions. The possible involvement of phospholipids in the synthesis of aryl metabolites
is discussed.
Received: 7 August 1998 / Accepted: 30 November 1998 相似文献
2.
Removal of organic pollutants and of nitrate from wastewater from the dairy industry by denitrification 总被引:3,自引:0,他引:3
The aim of this work was to remove nitrate-N and organic pollutants from wastewater of the dairy industry by denitrification.
An artificially prepared wastewater, containing 250 mg/l nitrate-N and 1.5 g/l whey powder, was completely denitrified with
removal of 90%–93% of the chemical oxygen demand (COD) of the whey powder by suspended or immobilized mixed cultures and by
a suspended or immobilized pure culture that was isolated from the mixed culture inoculum. For the above COD/nitrate-N ratio
of 6:1, the results indicated that the organic compounds of the wastewater served as electron donors for complete denitrification
and that there was no need to add an external carbon source. In batch denitrification assays the suspended or immobilized
mixed cultures proved to be more active and reacted faster than the isolated pure cultures. In continuous denitrification
processes with immobilized pure or mixed cultures, the alginate beads, used for immobilization, were not stable for more than
12 days of incubation. The mixed free cultures removed the nitrate-N and COD continuously with no change of their activity
for at least 15 days at an optimum hydraulic retention time of 0.27 days with a loading rate of 900 mg nitrate-N l−1 day−1.
Received: 13 October 1997 / Received revision: 16 December 1997 / Accepted: 19 December 1997 相似文献
3.
Characteristics of dipeptide transport in pig jejunum in vitro 总被引:4,自引:0,他引:4
Winckler C Breves G Boll M Daniel H 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(7):495-500
Characteristics of dipeptide transport in pig jejunum were investigated in vitro by applying the Ussing-chamber technique
and mucosal uptake studies. Addition of both glycyl-l-glutamine and glycyl-l-sarcosine (20 mmol · l−1) to the mucosal buffer solution significantly increased the short-circuit current by 2.60 ± 0.15 and 1.57 ± 0.20 μeq · cm−2 · h−1, respectively. Concentration-dependent changes in short-circuit current followed Michaelis-Menten kinetics with similar affinity
constants for both dipeptides. From unidirectional flux rates for radiolabelled glycyl-l-sarcosine, a net flux rate for glycyl-l-sarcosine of 49.8 ± 6.7 nmol · cm−2 · h−1 was calculated. In mucosal uptake experiments, the apical influx of 14C-labelled glycyl-l-sarcosine into isolated porcine mucosa was pH dependent and significantly inhibited by glycyl-l-glutamine. Moreover, RT-PCR studies with primers derived from rabbit PepT1 identified two PCR fragments of identical size
to rabbit PepT1 from pig intestinal mRNA preparations. In conclusion, our studies revealed key features of mammalian intestinal
peptide transporters and give evidence for a PepT1-like transporter in the pig jejunum that could significantly contribute
to the overall amino acid absorption from the gut.
Accepted: 30 June 1999 相似文献
4.
The use of silica gel prepared by sol-gel method and polyurethane foam as microbial carriers in the continuous degradation of phenol 总被引:5,自引:0,他引:5
A mixed microbial culture was immobilized by entrapment into silica gel (SG) and entrapment/ adsorption on polyurethane foam
(PU) and ceramic foam. The phenol degradation performance of the SG biocatalyst was studied in a packed-bed reactor (PBR),
packed-bed reactor with ceramic foam (PBRC) and fluidized-bed reactor (FBR). In continuous experiments the maximum degradation
rate of phenol (q
s
max) decreased in the order: PBRC (598 mg l−1 h−1) > PBR (PU, 471 mg l−1 h−1) > PBR (SG, 394 mg l−1 h−1) > FBR (PU, 161 mg l−1 h−1) > FBR (SG, 91 mg l−1 h−1). The long-term use of the SG biocatalyst in continuous phenol degradation resulted in the formation of a 100–200 μm thick
layer with a high cell density on the surface of the gel particles. The abrasion of the surface layer in the FBR contributed
to the poor degradation performance of this reactor configuration. Coating the ceramic foam with a layer of cells immobilized
in colloidal SiO2 enhanced the phenol degradation efficiency during the first 3 days of the PBRC operation, in comparison with untreated ceramic
packing.
Received: 2 December 1999 / Revision received: 2 February 2000 / Accepted: 4 February 2000 相似文献
5.
The influence of ammonia on the anaerobic degradation of peptone by mesophilic and thermophilic populations of biowaste was
investigated. For peptone concentrations from 5 g l−1 to 20 g l−1 the mesophilic population revealed a higher rate of deamination than the thermophilic population, e.g. 552 mg l−1 day−1 compared to 320 mg l−1 day−1 at 10 g l−1 peptone. The final degree of deamination of the thermophilic population was, however, higher: 102 compared to 87 mg NH3/g peptone in the mesophilic cultures. If 0.5–6.5 g l−1 ammonia was added to the mesophilic biowaste cultures, deamination of peptone, degradation of its chemical oxygen demand
(COD) and formation of biogas were increasingly inhibited, but no hydrogen was formed. The thermophilic biowaste cultures
were most active if around 1 g ammonia l−1 was present. Deamination, COD degradation and biogas production decreased at lower and higher ammonia concentrations and
hydrogen was formed in addition to methane. Studies of the inhibition by ammonia of peptone deamination, COD degradation and
methane formation revealed a K
i (50%) for NH3 of 92, 95 and 88 mg l−1 at 37 °C and 251, 274 and 297 mg l−1 at 55 °C respectively. This indicated that the thermophilic flora tolerated significantly more NH3 than the mesophilic flora. In the mesophilic reactor effluent 4.6 × 108 peptone-degrading colony-forming units (cfu)/ml were culturable, whereas in the thermophilic reactor effluent growth of only
5.6 × 107 cfu/ml was observed.
Received: 24 April 1998 / Received revision: 26 June 1998 / Accepted: 27 June 1998 相似文献
6.
S. Østergaard H. B. Aa. Theilgaard J. Nielsen 《Applied microbiology and biotechnology》1998,50(6):663-668
We have demonstrated that Penicillium chrysogenum possesses the l-cysteine biosynthetic enzyme O-acetyl-l-serine sulphhydrylase (EC 4.2.99.8) of the direct sulphhydrylation pathway. The finding of this enzyme, and thus the presence
of the direct sulphhydrylation pathway in P. chrysogenum, creates the potential for increasing the overall yield in penicillin production by enhancing the enzymatic activity of this
microorganism. Only O-acetyl-l-serine sulphhydrylase and O-acetyl-l-homoserine sulphhydrylase (EC 4.2.99.10) have been demonstrated to use O-acetyl-l-serine as substrate for the formation of l-cysteine. The purified␣enzyme did not catalyse the formation of l-homocysteine from O-acetyl-l-homoserine and sulphide, excluding the possibility that the purified enzyme was O-acetyl-l-homoserine sulphhydrylase with multiple substrate specificity. The purification enhanced the enzymatic specific activity
93-fold in relation to the cell-free extract. Two bands, showing exactly the same intensity, were present on a sodium dodecyl
sulphate/polyacrylamide gel, and the molecular masses of these were estimated to be 59 kDa and 68 kDa respectively. The K
m value for O-acetyl-l-serine and V
max of O-acetyl-l-serine sulphhydrylase were estimated to be 1.3 mM and 14.9 μmol/mg protein−1 h−1 respectively. The activity of the purified enzyme had a temperature optimum of approximately 45 °C, which is much higher
than the actual temperature for penicillin synthesis. Furthermore, O-acetyl-l-serine sulphhydrylase activity was to have a maximum in the range of pH 7.0–7.4.
Received: 20 March 1998 / Received revision: 27 July 1998 / Accepted: 12 August 1998 相似文献
7.
M. Helanto K. Kiviharju T. Granström M. Leisola A. Nyyssölä 《Applied microbiology and biotechnology》2009,83(1):77-83
l-Ribose is a rare and expensive sugar that can be used as a precursor for the production of l-nucleoside analogues, which are used as antiviral drugs. In this work, we describe a novel way of producing l-ribose from the readily available raw material l-arabinose. This was achieved by introducing l-ribose isomerase activity into l-ribulokinase-deficient Escherichia coli UP1110 and Lactobacillus plantarum BPT197 strains. The process for l-ribose production by resting cells was investigated. The initial l-ribose production rates at 39°C and pH 8 were 0.46 ± 0.01 g g−1 h−1 (1.84 ± 0.03 g l−1 h−1) and 0.27 ± 0.01 g g−1 h−1 (1.91 ± 0.1 g l−1 h−1) for E. coli and for L. plantarum, respectively. Conversions were around 20% at their highest in the experiments. Also partially purified protein precipitates
having both l-arabinose isomerase and l-ribose isomerase activity were successfully used for converting l-arabinose to l-ribose. 相似文献
8.
Takashi Nemoto Taisuke Watanabe Yutaka Mizogami Jun-ichi Maruyama Katsuhiko Kitamoto 《Applied microbiology and biotechnology》2009,82(6):1105-1114
The recombinant Pichia pastoris harboring an improved methionine adenosyltransferase (MAT) shuffled gene was employed to biosynthesize S-adenosyl-l-methionine (SAM). Two l-methionine (l-Met) addition strategies were used to supply the precursor: the batch addition strategy (l-Met was added separately at three time points) and the continuous feeding strategies (l-Met was fed continuously at the rate of 0.1, 0.2, and 0.5 g l−1 h−1, respectively). SAM accumulation, l-Met conversion rate, and SAM productivity with the continuous feeding strategies were all improved over the batch addition
strategy, which reached 8.46 ± 0.31 g l−1, 41.7 ± 1.4%, and 0.18 ± 0.01 g l−1 h−1 with the best continuous feeding strategy (0.2 g l−1 h−1), respectively. The bottleneck for SAM production with the low l-Met feeding rate (0.1 g L−1 h−1) was the insufficient l-Met supply. The analysis of the key enzyme activities indicated that the tricarboxylic acid cycle and glycolytic pathway
were reduced with the increasing l-Met feeding rate, which decreased the adenosine triphosphate (ATP) synthesis. The MAT activity also decreased as the l-Met feeding rate rose. The reduced ATP synthesis and MAT activity were probably the reason for the low SAM accumulation when
the l-Met feeding rate reached 0.5 g l−1 h−1. 相似文献
9.
Biosurfactants containing rhamnose and β-hydroxydecanoic acid and called rhamnolipids are reviewed with respect to microbial
producers, their physiological role, biosynthesis and genetics, and especially their microbial overproduction, physicochemical
properties and potential applications. With Pseudomonas species, more than 100 g l−1 rhamnolipids were produced from 160 g l−1 soybean oil at a volumetric productivity of 0.4 g l−1 h−1. The individual rhamnolipids are able to lower the surface tension of water from 72 mN m−1 to 25–30 mN m−1 at concentrations of 10–200 mg l−1. After initial testing, rhamnolipids seem to have potential applications in combating marine oil pollution, removing oil
from sand and in combating zoosporic phytopathogens. Rhamnolipids are also a source of l-rhamnose, which is already used for the industrial production of high-quality flavor components.
Received: 1 July 1998 / Received revision: 11 September 1998 / Accepted: 13 September 1998 相似文献
10.
J. Q. Liu M. Odani T. Dairi N. Itoh S. Shimizu H. Yamada 《Applied microbiology and biotechnology》1999,51(5):586-591
A new enzymatic resolution process was established for the production of l-threo-3-[4-(methylthio)phenylserine] (MTPS), an intermediate for synthesis of antibiotics, florfenicol and thiamphenicol, using
the recombinant low-specificity d-threonine aldolase from Arthrobacter sp. DK-38. Chemically synthesized dl-threo-MTPS was efficiently resolved with either the purified enzyme or the intact recombinant Escherichiacoli cells overproducing the enzyme. Under the optimized experimental conditions, 100 mM (22.8 g l−1) l-threo-MTPS was obtained from 200 mM (45.5 g l−1) dl-threo-MTPS, with a molar yield of 50% and a 99.6% enantiomeric excess.
Received: 2 September 1998 / Received revision: 27 October 1998 / Accepted: 29 November 1998 相似文献
11.
The use of amiloride to uncouple branchial sodium and proton fluxes in the brown trout, Salmo trutta
I. D. Nelson W. T. W. Potts H. Huddart 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(2):123-128
Resting proton, ammonium and sodium fluxes in Salmo trutta were 492.6 ± 19.5 (n = 29); 122.9 ± 34.2 (n = 28) and 277.1 ± 18.5 (n = 50) μmol · kg−1 · h−1, respectively. The resting transepithelial potential was found to be composed of three successive potentials, the outermost
averaging −7.36 ± 0.19mV, the second, −14.3 ± 1.4 mV and the third −37 ± 1.7 mV. Amiloride inhibits the proton, ammonium and
sodium fluxes in a dose-dependent manner at concentrations of 0.5 mmol · 1−1 and 0.1 mmol · l−1, but at 0.01 mmol · l−1, proton and ammonium fluxes remained at control levels whilst the sodium was reduced to 70.59 ± 7.29 μmol · kg−1 · h−1. The trans-epithelial potential was effected in a bi-phasic manner by 0.5 mmol · l−1 amiloride. An initial hyperpolarisation of ca. 6 mV was followed by a sustained depolarisation of ca. 14 mV (towards zero)
which persisted until the amiloride was washed off the gill. The initial hyperpolarisation was thought to reflect a rapid
inhibition of a positive inward sodium current and the subsequent depolarisation was due to the inhibition of a positive outward
current (proton) which would abolish the transepithelial potential. However, at 0.01 mmol · l−1 only the hyperpolarisation was seen, due to the inhibition of only the inward sodium current. Acetazolamide (0.1 mmol · l−1) was found to have no significant effect on the proton, ammonium and sodium fluxes. These results indicate that the proton
and sodium fluxes across the gill of the freshwater trout are not tightly linked. While this suggests that the trout gill
resembles the model of Ehrenburg et al. (1985) of sodium uptake in frog skin, the apical potentials measured in the pavement
epithelial cell(s) are too low to account for sodium uptake unless the activity of the sodium in the cells is very low.
Accepted: 8 August 1996 相似文献
12.
S. S. Sudge K. B. Bastawde D. V. Gokhale U. R. Kalkote T. Ravindranathan 《Applied microbiology and biotechnology》1998,49(5):594-599
About 1000 bacterial colonies isolated from sea water were screened for their ability to convert dl-5-phenylhydantoin to d(−)N-carbamoylphenylglycine as a criterion for the determination of hydantoinase activity. The strain M-1, out of 11 hydantoinase-producing
strains, exhibited the maximum ability to convert dl-5-phenylhydantoin to d(−)N-carbamoylphenylglycine. The strain M-1 appeared to be a halophilic Pseudomonas sp. according to morphological and physiological characteristics. Optimization of the growth parameters revealed that nutrient
broth with 2% NaCl was the preferred medium for both biomass and enzyme production. d-Hydantoinase of strain M-1 was not found to be inducible by the addition of uracil, dihydrouracil, β-alanine etc. The optimum
temperature for enzyme production was about 25 °C and the organism showed a broad pH optimum (pH 6.5–9.0) for both biomass
and hydantoinase production. The organism seems to have a strict requirement of NaCl for both growth and enzyme production.
The optimum pH and temperature of enzyme activity were 9–9.5 and 30 °C respectively. The biotransformation under the alkaline
conditions allowed the conversion of 80 g l−1
dl-5-phenylhydantoin to 82 g l−1
d(−)N-carbamoylphenylglycine within 24 h with a molar yield of 93%.
Received: 15 September 1997 / Received revision: 5 January 1998 / Accepted: 6 January 1998 相似文献
13.
J. M. Obón J. R. Maiquez M. Cánovas H.-P. Kleber J. L. Iborra 《Applied microbiology and biotechnology》1999,51(6):760-764
The use of a biological procedure for l-carnitine production as an alternative to chemical methods must be accompanied by an efficient and highly productive reaction
system. Continuous l-carnitine production from crotonobetaine was studied in a cell-recycle reactor with Escherichia coli O44 K74 as biocatalyst. This bioreactor, running under the optimum medium composition (25 mM fumarate, 5 g/l peptone), was
able to reach a high cell density (26 g dry weight/l) and therefore to obtain high productivity values (6.2 g l-carnitine l−1 h−1). This process showed its feasibility for industrial l-carnitine production. In addition, resting cells maintained in continuous operation, with crotonobetaine as the only medium
component, kept their biocatalytic capacity for 4 days, but the biotransformation capacity decreased progressively when this
particular method of cultivation was used.
Received: 10 December 1998 / Received revision: 19 February 1999 / Accepted: 20 February 1999 相似文献
14.
The development of a rapid protocol for high-efficiency somatic embryogenesis and plant regeneration from seed-derived embryogenic
callus cultures of California poppy (Eschscholzia californica Cham.) is reported. The optimized procedure required less than 13 weeks from the initiation of seed cultures to the recovery
of plantlets and involved the sequential transfer of cultures onto solid Murashige and Skoog basal medium containing three
different combinations of growth regulators. All steps were performed at 25 °C. Friable primary callus was induced from seeds
of E. californica cultured on medium supplemented with 1.0 mg l−1 2,4-dichlorophenoxyacetic acid. The primary callus was transferred to medium containing 1.0 mg l−1 1-naphthaleneacetic acid and 0.5 mg l−1 6-benzylaminopurine to establish embryogenic callus and promote somatic embryogenesis. Regenerated plantlets were recovered
after the conversion of somatic embryos on medium containing 0.05 mg l−1 6-benzylaminopurine and showed normal development. Embryogenic callus was induced at a frequency of 85%, an average of 45
somatic embryos were produced per callus, 90% of the somatic embryos converted, and about 70% of the plantlets were recovered
in soil. The growth rate of somatic embryo-derived shoots could be increased by gibberellic acid treatment, but the resulting
plantlets were hyperhydritic.
Received: 14 February 1999 / Revision received: 27 April 1999 / Accepted: 14 May 1999 相似文献
15.
Biotransformation of benzaldehyde to l-phenylacetylcarbinol (l-PAC) as a key intermediate for l-ephedrine synthesis has been evaluated using immobilized Candida utilis. During biotransformation, the benzaldehyde level and respiratory quotient significantly affected both l-PAC and by-product benzyl alcohol formation. By controlling the benzaldehyde level at 2 g/l, maintaining a respiratory quotient of 5–7 and pulse feeding glucose, a final concentration of 15.2 g/l l-PAC was achieved in a fed-batch process. This compares with previous published results of 10–12 g/l in batch culture and 10 g/l l-PAC in a semicontinuous process with immobilized Saccharomyces cerevisiae. In a single stage continuous process with immobilized C. utilis, the steady state l-PAC concentration was significantly reduced because of the sustained toxic effects of benzaldehyde. 相似文献
16.
Continuous production of l(+)-lactic acid by Lactobacillus casei in two-stage systems 总被引:2,自引:0,他引:2
Bruno-Bárcena JM Ragout AL Córdoba PR Siñeriz F 《Applied microbiology and biotechnology》1999,51(3):316-324
A two-stage two-stream chemostat system and a two-stage two-stream immobilized upflow packed-bed reactor system were used
for the study of lactic acid production by Lactobacillus casei subsp casei. A mixing ratio of D
12/D
2 = 0.5 (D = dilution rate) resulted in optimum production, making it possible to generate continuously a broth with high lactic acid
concentration (48 g l−1) and with a lowered overall content of initial yeast extract (5 g l−1), half the concentration supplied in the one-step process. In the two-stage chemostat system, with the first stage at pH
5.5 and 37 °C and a second stage at pH 6.0, a temperature change from 40 °C to 45 °C in the second stage resulted in a 100%
substrate consumption at an overall dilution rate of 0.05 h−1. To increase the cell mass in the system, an adhesive strain of L. casei was used to inoculate two packed-bed reactors, which operated with two mixed feedstock streams at the optimal conditions
found above. Lactic acid fermentation started after a lag period of cell growth over foam glass particles. No significant
amount of free cells, compared with those adhering to the glass foam, was observed during continuous lactic acid production.
The extreme values, 57.5 g l−1 for lactic acid concentration and 9.72 g l−1 h−1 for the volumetric productivity, in upflow packed-bed reactors were higher than those obtained for free cells (48 g l−1 and 2.42 g l−1 h−1) respectively and the highest overall l(+)-lactic acid purity (96.8%) was obtained in the two-chemostat system as compared with the immobilized-cell reactors (93%).
Received: 4 December 1997 / Received revision: 23 February 1998 / Accepted: 14 March 1998 相似文献
17.
In order to improve the production rate of l-lysine, a mutant of Corynebacterium glutamicum ATCC 21513 was cultivated in complex medium with gluconate and glucose as mixed carbon sources. In a batch culture, this
strain was found to consume gluconate and glucose simultaneously. In continuous culture at dilution rates ranging from 0.2
h−1 to 0.25 h−1, the specific l-lysine production rate increased to 0.12 g g−1 h−1 from 0.1 g g−1 h−1, the rate obtained with glucose as the sole carbon source [Lee et al. (1995) Appl Microbiol Biotechnol 43:1019–1027]. It
is notable that l-lysine production was observed at higher dilution rates than 0.4 h−1, which was not observed when glucose was the sole carbon source. The positive effect of gluconate was confirmed in the shift
of the carbon source from glucose to gluconate. The metabolic transition, which has been characterized by decreased l-lysine production at the higher glucose uptake rates, was not observed when gluconate was added. These results demonstrate
that the utilization of gluconate as a secondary carbon source improves the maximum l-lysine production rate in the threonine-limited continuous culture, probably by relieving the limiting factors in the lysine
synthesis rate such as NADPH supply and/or phosphoenolpyruvate availability.
Received: 16 May 1997 / Received revision: 28 August 1997 / Accepted: 29 August 1997 相似文献
18.
L. Lesage-Meessen M. Haon M. Delattre J.-F. Thibault B. Colonna Ceccaldi M. Asther 《Applied microbiology and biotechnology》1997,47(4):393-397
The effects of adding cellobiose on the transformation of vanillic acid to vanillin by two strains of Pycnoporus cinnabarinus MUCL39532 and MUCL38467 were studied. When maltose was used as the carbon source in the culture medium, very high levels
of methoxyhydroquinone were formed from vanillic acid. When cellobiose was used as the carbon source and/or added to the culture
medium of P. cinnabarinus strains on day 3 just before vanillic acid was added, it channelled the vanillic acid metabolism via the reductive route
leading to vanillin. Adding 3.5 g l−1 cellobiose to 3-day-old maltose cultures of P. cinnabarinus MUCL39532 and 2.5 g l−1 cellobiose to 3-day-old cellobiose cultures of P. cinnabarinus MUCL38467, yielded 510 mg l−1 and 560 mg l−1 vanillin with a molar yield of 50.2 % and 51.7 % respectively. Cellobiose may either have acted as an easily metabolizable
carbon source, required for the reductive pathway to occur, or as an inducer of cellobiose:quinone oxidoreductase, which is
known to inhibit vanillic acid decarboxylation.
Received: 24 July 1996 / Received revision: 29 November 1996 / Accepted: 29 November 1996 相似文献
19.
S. M. E. Guirguis J. C. Yee D. F. Stiffler 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(5):328-334
The skin of intact, free-swimming Xenopus laevis transports Ca2+ inwardly in a manner that is proportional to the external [Ca2+] up to about 0.3 mmol · l−1, saturates above 0.3 mmol · l−1, and is opposed to the electrochemical gradient. Efflux is relatively constant at external concentrations between 0.016 and
0.6 mmol · l−1; net flux which is negative below 0.125 mmol · l−1 becomes positive above this external [Ca2+]. Allometric analysis suggests that both Ca2+ influx and efflux scale to the 2/3 power approximately like surface area. There were no significant differences in influx
between summer and fall animals; however, efflux was greater in the fall and this resulted in a change from positive balance
in the summer to negative balance in the fall. Isolated skins were shown to support a Ca2+ uptake rate of nearly 30 nmol · cm−2 · h−1. The phenylalkylamine verapamil in the apical bathing solution significantly inhibited this at 25 μmol · l−1. The benzothiazepine diltiazem was also effective at 50 μmol · l−1 while the dihydropyradine nifedipine was ineffective up to 100 μmol · l−1. The inorganic ion La3+ was effective at blocking Ca2+ uptake at 300 μmol · l−1; Ni2+ was also effective at 500 μmol · l−1 but Co2+ was ineffective up to 500 μmol · l−1. These results suggest that apical calcium channels in Xenopuslaevis skin have properties similar to mammalian L-channels and fish gill Ca2+ channels.
Accepted: 23 January 1997 相似文献
20.
T. Ohshiro M. Shinji Y. Morita Y. Takayama Y. Izumi 《Applied microbiology and biotechnology》1997,48(4):546-548
Microorganisms capable of cleaving the urethane bond of t-butoxycarbonyl (Boc) amino acids in a whole-cell reaction were screened among stock cultures, and Corynebacterium aquaticum IFO12154 was the most promising. The conversion of Boc-Ala to Ala was stimulated by CoSO4 in the medium and reaction mixture. The optimum whole-cell concentration was 25 mg lyophilized cells/ml. Boc-l-Met was the best substrate for this reaction, and other Boc-L-amino acids, as well as benzyloxycarbonyl-l-amino acids with hydrophobic residues, were also good substrates. Boc-d- and Z-d-amino acids were inert. When the reactions had proceeded for 24 h with each substrate at 10 mM, the molar conversion rates
from Boc-l-, dl- and d-Met were 100%, 50%, and 0% respectively. From 150 mM Boc-l-Met, 143 mM l-Met was formed at a molar yield of 95.3%.
Received: 3 September 1996 / Received last revision: 7 April 1997 / Accepted: 19 April 1997 相似文献