Summary A mathematical model simulating the behaviour or Streptomyces aureofaciens in batch culture under conditions when tetracyclines are synthesized in excessive amounts has been formulated. The response of the mathematical model to the experimental conditions applied corresponds with data obtained in the experiments. The mathematical model demonstrated that the level of tetracycline production is determined during the period of culture growth beginning with exhaustion of inorganic phosphate from the medium and ending with inhibition of the synthesis of enzymes caused by the synthesized tetracyclines. Further tetracycline synthesis is then proportional to the amount of enzymes synthesized in this interval.List of symbols
E
Activity of ACT-oxygenase (10×nkat/g)
-
P
Product concentration (mg/l)
-
k1-k6
Rate constants
-
KS
Saturation constant (g sugar/l)
-
KI1
Inhibition constant (mg product/l)
-
KI2
Inhibition constant (mM phosphate/l)
-
KI3
Inhibition constant (mg product/l)
-
S1
Substrate sucrose (g sugar/l)
-
S2
Substrate concentration — phosphate (mM/l)
-
rP
Specific rate of product formation (mg product/g · h)
-
rE
Specific rate of enzyme synthesis (10×nkat/g2 · h), Expressed by activity units
-
t
Cultivation time (hour)
-
X
Biomass dry weight (g/l)
-
YS/X
Yield coefficient
-
Specific growth rate (h-1) 相似文献
Radioiodination of highly purified human follicle-stimulating hormone (hFSH) (4000 IU/mg) was performed every other week for 23 weeks using 2 mCi carrier free Na 125I (Amersham Corp., 15 mCi/μg I2) in the presence of lactoperoxidase. Incorporation of 125I into hFSH was determined by the method of [7.]Biochem. J.89, 114). Hormone binding was studied in vitro under steady-state conditions (16 h, 20°C) using different calf testis membrane preparations having similar receptor characteristics. Each 125I-hFSH preparation was characterized for maximum bindability, specific activity of bindable radioligand as determined by self-displacement analysis, and by determination of Ka and Rt. Incorporation of 125I into FSH was relatively constant over the large number of experiments (62.4 ± 6.4 μCi/μg; n = 23). By comparison, however, specific radioactivity of the receptor bindable fraction of 125I-hFSH was related to the lot of 125I utilized, and was significantly (P ≤ 0.01) lower and more variable (28.7 ± 10.5 μCi/μg). Maximum bindability of 125I-hFSH was not correlated to specific activity (r = 0.06) but was negatively correlated to hFSH 125I incorporation (r = −0.47; P ≤ 0.05). These observations demonstrate the need to assess the quality of each batch of radioligand before undertaking radioligand-receptor assays and suggest that differences in Na125I lots affect specific radioactivity of the radioligand and its receptor binding characteristics. 相似文献
The applicability of emission of the N3Λσ triplet states of molecular hydrogen for spectral diagnostics of the positive column of a dc glow discharge in hydrogen at translational gas temperatures of 360–600 K, specific absorbed powers of 0.8–4.25 W/cm, gas pressures of p = 0.3–15.0 Torr, reduced fields of E/N = 30–130 Td, and electron densities of ne = 4.0 × 109–6.5 × 1010 cm–3 is analyzed by using an advanced level-based semi-empirical collisional?radiative model. It is found that secondary processes make the main contribution to the population and decay of the N3Λσ = a3Σ+g, c3Πu, g3Σ+g, h3Σ+g, and i3Πg triplet states. The dipole-allowed transitions e3Σ+g → a3Σ+g, f3Σ+g → a3Σ+g, g3Σ+g and k3Πu → a3Σ+g can be used for spectral diagnostics of a dc discharge within a simplified coronal model. 相似文献
Zusammenfassung Bei der Bestimmung der Anzahl Bakterien in frisch genommenen Seewasserproben mit dem Plattengußverfahren reduziert eine Agarmenge von über 10 ml die Anzahl sich entwickelnder Kolonien. Die erhaltenen Zahlen sind im allgemeinen am höchsten und die Ergebnisse am besten reproduzierbar, wenn genau 10 ml des Nähragars benutzt wird im Gegensatz zu unbestimmten Mengen zwischen 5 und 30 ml. Obgleich auch andere Faktoren eine Rolle spielen, wird der ungünstige Einfluß von Agarmengen, die merklich größer als 10 ml sind, in erster Linie den langsameren Abkühlungsraten während des üblichen Plattengußverfahrens zugeschrieben. Wenn Nähragar von 42° C bei Raumtemperatur (22–24° C) in Pyrex-Petrischalen gegossen wurde, kühlten 10 ml in ca. 1 min. auf 30° C ab, während 5 bis 24 min. gebraucht wurden, um Agarmengen von 20 bis 50 ml von 42° C auf 30° C abzukühlen. Viele marine Bakterien werden geschädigt, wenn sie Temperaturen ausgesetzt werden, die über 30° C liegen, wobei das Ausmaß der Schädigung von der Einwirkungszeit abhängt. Deswegen ist es überaus wichtig, daß der Agar vor dem Gießen auf 42° C gekühlt wird. Die Abkühlungsrate des Agarmediums in den Platten wird von der Beschaffenheit und der Temperatur der Tischoberfläche, auf der die Platten stchen, beeinflußt.
Plating the heterogeneous bacteria occuring naturally in samples of raw sea water with volumes of molten nutrient agar exceeding 10 ml reduces the number of colonies which develop. Plate counts on replicate samples of sea water are generally highest and results are more nearly reproducible when 10 ml of nutrient agar is used rather than volumes ranging randomly from 5 to 30 ml. Although other factors are involved, the adverse effects of volumes of nutrient agar appreciable larger than 10 ml are attributed primarily to the slower cooling rates during conventional plating procedures. When nutrient agar medium at 42° C was poured into pyrex Petri dishes at room temperature (22–24° C), 10 ml of the medium cooled to 30° C in about one minute, whereas from about 5 to 24 minutes were required for 20 to 50 ml of the medium to cool from 42° C down to 30 ° C. Many marine bacteria are injured by being subjected to temperatures higher than 30° C, the extent of the injury being a function of time. Therefore, it is of paramount importance that agar be cooled to 42° C prior to pouring. The rate at which agar medium cools in plates is influenced by the composition and temperature of the table top on which the plates rest.
Contribution from the Scripps Institution of Oceanography, University of California, La Jolla, California. 相似文献
In this study, the spatial distribution of brood-bearing females of five species of limnetic cladocerans (Daphnia cucullata, D. longispina, Bosmina coregoni, B.longirostris, Diaphanosoma brachyurum) in the deep mesotrophic lake in relation to the predation pressure of planktivorous fish (roach Rutilus rutilus, perch Perca fluviatilis, catfish Ictalurus nebulosus, white fish Coregonus albula, bleak Alburnus alburnus), and planktonic invertebrates (cyclopoids Mesocyclops leuckartii, Thermocyclops oithonoides, T.crassus, and cladoceran Leptodora kindtii) as well as some environmental variables was estimated. Most cladocerans showed apparent differences in horizontal distribution (ANOVA F = 0.2–0.45, P < 0.05) in the littoral zone and lack of such differences in the pelagic zone (F = 0.07–0.13, P > 0.05). Vertical distribution of most species, in turn, showed a clear pattern in the pelagic zone (F = 0.31–0.39, P < 0.05) and less regularities in the littoral zone (F = 0.15–029, P > 0.05). The differences in spatial distribution of non-predated and predated species suggest that predation pressure, but not predatory type, was an important factor structuring their distribution. Other factors that affected their distribution were conductivity, dissolved oxygen, TOC and macrophyte biomass; however, most of those variables better explained the distribution of brood-bearing cladocerans in the vertical than horizontal aspect. 相似文献
Remarkable qualitative and quantitative differences in non-glycosylated triterpenoid profiles of twelve Dioscorea spp. leaves were demonstrated with the use of GC–MS/FID analysis. The total content of tetracyclic triterpenoids and their esters ranged from 397 μg/g of dry leaf weight in D. bulbifera to 762 μg/g d.w. in D. discolor and 777 μg/g d.w. in D. alata. Three main phytosterols, i.e. campesterol (1), sitosterol (2) and stigmasterol (3) were found in extracts from all analyzed species in total amount ranging from 316 μg/g in D. bulbifera to 676 μg/g of dry leaf weight in D. hispida, with either sitosterol (2) or stigmasterol (3) as predominant in the profile. Extracts from D. hispida and D. purpurea leaves were distinguished from the others by particularly high amount of campesterol (1). In the majority of the species, except for D. caucasica, other tetracyclic triterpenoids were found: cycloartanol (4), 24-methylenecycloartanol (5) and cycloeucalenol (6). Less common steroids, stigmastan-3-en-6β-ol (7) and ergosta-7,22-dien-3β-ol (8) were detected in D. japonica. The significant content (992 μg/g) of pentacyclic triterpenoids of ursane, oleanane, taraxastane and taraxerene (friedooleanane)-type carbon skeletons, i.e. α-amyrin (9), β-amyrin (10), taraxasterol (11) and taraxerol (12), respectively, was found in D. caucasica. The obtained results supplement the knowledge of biochemical diversity of Dioscorea genus. 相似文献
Hfq is an RNA-binding protein that participates in the regulatory activity of small non-coding RNAs (sRNAs) in many species of bacteria. Hfq protein was first crystallized from Staphylococcus aureus and this crystal structure constitutes a hallmark for bacterial Sm-like proteins. Paradoxically, however, the functional relevance/role of S. aureus Hfq (HfqSA) remains uncertain, as growing evidence suggests that the hfqSA gene is expressed at very low levels or unexpressed in many S. aureus strains. To gather further insight, in the present work we exchanged the structural portion of the hfq gene of Salmonella enterica serovar Typhimurium (hfqSTM) with hfqSA and analyzed the effects of the replacement on various Hfq-related phenotypes. Our results show that the replacement strain – in spite of expressing HfqSA at levels comparable to HfqSTM in wild-type Salmonella – behaves as an hfq null mutant in three discrete small RNA-mediated regulatory responses. These defects correlate with an abrupt reduction in the intracellular concentration of sRNAs, as observed in an hfq null mutant. Failure of HfqSA to protect Salmonella sRNAs from degradation suggests that HfqSa does not bind to these sRNAs. A parallel study with the Borrelia burgdorferi hfq gene (hfqBB) gave essentially identical results: when made from a single copy chromosomal gene, HfqBB fails to substitute for HfqSTM in sRNA-mediated regulation. 相似文献
Despite the progress in studies of the properties and functions of low-threshold calcium channels (LTCCs) [1], the mechanisms
of their selectivity and permeability remain unstudied in detail. We performed a comparative analysis of the selectivity of
three cloned pore-forming LTCC subunits (α1G, α1H, and α1I) functionally expressed in Xenopus oocytes with respect to bivalent alkaline-earth metal cations (Ba2+, Ca2+, and Sr2+. The relative conductivities (G) of these channels were determined according to the amplitudes of macroscopic currents (I) and potentials of zero currents (E). The currents were recorded after preliminary intracellular injection of a fast calcium buffer, BAPTA, in order to suppress
the endogenous calcium-dependent chloride conductivity. Channels formed by α1G subunits demonstrated the following ratios
of the amplitudes of macroscopic currents and potentials of zero current: ICa:IBa:ISr = 1.00:0.75:1.12 and ECa ≈ EBa ≈ ESr. For channels that were formed by α1H and α1I subunits, these ratios were as follows: ICa:IBa:ISr = 1.00:1.20:1.17, ECa ≈ EBa ≈ ESr and ICa:IBa:ISr = 1.00:1.48: 1.45, ECa ≈ EBa ≈ ESr respectively. The different macroscopic conductivities and similar potentials of zero current typical of α1G and α1I channels
indicate that, probably, various bivalent cations can in a differential manner influence the stochastic parameters of functioning
of these channels. At the same time, channels formed by α1H subunits are characterized by more positive potentials of zero
current for Ca2+. It seems possible that the selectivity of the above channels is determined by mechanisms that mediate the selectivity of
most high-threshold calcium channels (more affine binding of Ca2+ inside the pore).
Neirofiziologiya/Neurophysiology, Vol. 37, No. 4, pp. 319–329, July–August, 2005. 相似文献
Several mutants of tomatoes are known in which the carotene content of the fruit is markedly altered qualitatively and quantitatively from that found in the standard red tomato variety. These selections are: rr (yellow flesh, low carotene); tt (tangerine, orange, proneurosporene and prolycopene); at at (apricot, low in acyclic carotenes); ogc ogc (crimson, high in lycopene); Verkerk 377-2αα (probably identical to vircscent orange vo vo, high in ζ-carotene); B B (Hi-β, high in β-carotene), and Del Del (Hi-δ, high in δ-carotenc). Studies of carotene synthesis from [1-14C]isopentenyl pyrophosphate, [14C]phytoene, and [14C]lycopcne by soluble enzyme systems obtained from fruits of these selections have shown unexpected enzyme activities. All selections evidence activity for the synthesis of phytoene. All mutants have also been found to contain an enzyme system for the synthesis of β-carotenefrom lycopene. Three of the selections analyzed (rr, at at, and ogc ogc) also contain an enzyme system for the conversion of lycopene to α-carotene and the variants rr and tt contain an enzyme for the synthesis of poly-cis-carotencs from isopentenyl pyrophosphate and phytocne.The reasons for the discrepancies that are observed between carotene composition of fruit of field-grown tomato selections and enzyme activities for carotene synthesis by cell-free preparations obtained from these fruits are not presently known. It is obvious, however, that either inhibitors are present, cofactors are missing, or there are permeability barriers to substrate or cofactor transport into plastids of selections in which enzyme activities are not expressed in field-grown fruit. Further investigations will be required for clarification of this problem. 相似文献
Nucleophilic Michael-type additions to aldohexofuranoid 3-C-methylene derivatives, namely, 3-deoxy-1,2:5,6-di-O-isopropylidene-3-C-nitromethylene-α-d-ribo-hexofuranose and 3-C-[cyano(ethoxycarbonyl)methylene]-3-deoxy-1,2:5,6-di-O-isopropylidene-α-d-ribo-hexofuranose employing phase-transfer catalysis, afforded novel gem-di-C-substituted sugars. The conversion of 3-deoxy-1,2:5,6-di-O-isopropylidene-3-C-methyl-3-C-nitromethyl-α-d-allo-hexofuranose into a 3-C-hydroxymethyl-3-C-methyl derivative with titanium trichloride, and that of the nitromethyl groups of 3-deoxy-1,2:5,6-di-O-isopropylidene-3,3-di-C-nitromethyl-α-d-ribo-hexofuranose, and 3-deoxy-1,2:5,6-di-O-isopropylidene-3-C-methyl-3-C-nitromethyl- and -3-C-nitromethyl-α-d-allo-hexofuranose into cyano groups with phosphorus trichloride in pyridine is also described. 相似文献
Complexes cis,trans-Fe(CO)2(PMe3)2RR′ (R = CH3, R′ = Ph (2); R = CH3, R′ = CHCH2 (3); R = CHCH2, R′ = Ph (4); R = R′ = CHCH2 (5); R = R′ = CH3 (6)) were prepared by reaction of cis,trans-Fe(CO)2(PMe3)2RCl (1) with organolithium reagents LiR′. All complexes were characterized in solution by IR and 1H, 31P and, in a few cases, 13C NMR mono- and bi-dimensional spectroscopies. Complexes 5 and 6 were structurally characterized by X-ray diffractometric methods. In solution complexes 2, 3 and 4 undergo slowly coupling of the σ-hydrocarbyl substituents leading to Fe(CO)3(PMe3)2 and other decomposition products. Complex 6 was very stable in solution in the absence of nucleophiles and in the solid state. Complex 5 transformed through intramolecular coupling of the vinyl groups into Fe(CO)(PMe3)2(η4-butadiene) (7), which was characterized in solution by IR and NMR spectroscopies. 相似文献
There are some analytical solutions of the Penna model of biological aging; here, we discuss the approach by Coe et al. (Phys.
Rev. Lett. 89, 288103, 2002), based on the concept of self-consistent solution of a master equation representing the Penna
model. The equation describes transition of the population distribution at time t to next time step (t + 1). For the steady state, the population n(a, l, t) at age a and for given genome length l becomes time-independent. In this paper we discuss the stability of the analytical solution at various ranges of the model
parameters—the birth rate b or mutation rate m. The map for the transition from n(a, l, t) to the next time step population distribution n(a + 1, l, t + 1) is constructed. Then the fix point (the steady state solution) brings recovery of Coe et al. results. From the analysis
of the stability matrix, the Lyapunov coefficients, indicative of the stability of the solutions, are extracted. The results
lead to phase diagram of the stable solutions in the space of model parameters (b, m, h), where h is the hunt rate. With increasing birth rate b, we observe critical b0 below which population is extinct, followed by non-zero stable single solution. Further increase in b leads to typical series of bifurcations with the cycle doubling until the chaos is reached at some bc. Limiting cases such as those leading to the logistic model are also discussed. 相似文献
Pseudobactin is a structurally complex and physiologically important siderophore (microbial iron chelator) from Pseudomonas putida- fluorescens. Various fragments of the unusual peptide component of pseudobactin listed below were prepared by solution-phase peptide synthesis. L -Lys· D -threo-β-OH Asp· L -Ala· D -allo-Thr· L -Ala L -Lys· D -threo-βOH Asp· L -Ala· D -allo-Thr D -threo-β-OH Asp· L -Ala· D - allo-Thr· L -Ala· D -N-OH-cycloOrn D -threo-β-OH-Asp· L -Ala· D -allo-Thr· L -Ala L -Ala· D -allo-Thr· L - Ala· D -N-OH-cycloOrn A class of related peptides named pseudomycins have shown promising antifungal activity. To examine if these peptide fragments above would elicit similar activity, the fragments were tested and found to have no antifungal activity in limited bioassays. 相似文献
A comparison of vanadium-rich activity of three species fungi of Basidiomycetes, Ganoderma lucidum, Coprinus comatus, and Grifola frondosa, was studied. By fermentation and atomic absorption spectroscopy analysis, the biomass of G. lucidum and G. frondosa declined rapidly when the concentration of vanadium exceeded 0.3% but the biomass of C. comatus did not decline rapidly until the concentration of vanadium exceeded 0.4% and the content of vanadium accumulated in the
mycelia was 3529.3 μg/g. After the mice were administered (intragastrically) with vanadium-rich C. comatus, the blood glucose of alloxan-induced hyperglycemic mice was decreased (p < 0.05) and the body weight of the alloxan-induced hyperglycemic mice was increased gradually. Thus, we selected C. comatus to absorb vanadium and chose 0.4% as the optimal concentration of vanadium for the pharmacological works. 相似文献
Stopped-flow kinetic studies of the formation of ferrioxamine B were performed. Formation of the complex follows the rate law where Ka is the acid dissociation constant of the iron(III) aquo species in 0.1 M formate buffer. At 25°C k1 = 3.94 × 102M?1 sec?1, k2Ka = 1.18 × 10?1 sec?1, k3 = 3.6 × 10?1 sec?1. Activation parameters for k1 are ΔH≠ = 11.7 kcal mole?1 and ΔS≠ = ?8 cal K?1 mole?1. An associative mechanism is proposed. Attachment of the first chelate ring is the slow step and favorably positions the second chelate ring for attachment. Coordination of two chelate rings favorably positions the third chelate ring for attachment. These results are compared to kinetics of formation of model complexes and to a previous study of the formation of ferrioxamine B in which attachment of the third chelate ring was proposed as the slow step 相似文献
Genomes of various hyperthermophilic and extremely thermophilic prokaryotes were analyzed with respect to size, physical
organization, and 16S rDNA copy number. Our results show that all the genomes are circular, and they are in the size range
of 1.6–1.8 Mb for Pyrodictium abyssi, Methanococcus igneus, Pyrobaculum aerophilum, Archaeoglobus fulgidus, Archaeoglobus lithotrophicus, and Archaeoglobus profundus (the two bacteria Fervidobacterium islandicum and Thermosipho africanus possess genomes of 1.5-Mb size). A systematic study of all validly described species of the order Sulfolobales revealed the existence of two classes of genome size for these archaea, correlating with phylogenetic analyses. The Metallosphaera–Acidianus group, plus Sulfolobus metallicus, have genomes of ca. 1.9 Mb; the other members of the order Sulfolobales group possess genomes >2.7 Mb. The special case of Stygiolobus azoricus is discussed.
Received: August 10, 1997 / Accepted: January 1, 1998 相似文献