Uptake of amino acids by actidione-treated yeast cells

Uptake of glyeine,l-cysteine,l-leucine,l-methionine,l-aspartic acid andl-lysine was investigated in resting cells ofSaccharomyces cerevisiae treated with 0.3mm actidione for blocking protein synthesis. The amino acids were taken up against substantial concentration gradients (up to nearly 1,000∶1 for μm l-cysteine and glycine). They were present in the free form inside the cells. Their unidirectional transmembrane fluxes were under a negative feedback control by the intracellular concentration of the amino acid involved. The amino acids tested apparently employed more than one transport agéncies for their membrane passage, the half-saturation constants being 6.2–7.7×10⁻⁴ m for glycine, 2.5×10⁻⁴ m forl-cysteine, 6×10⁻⁵ and 4×10⁻⁴ m forl-lysine, 3×10⁻⁵ and 6×10⁻⁴ m forl-methionine, 7–18×10⁻⁵ and 1.6×10⁻³ m forl-aspartic acid and 6×10⁻⁵ and 2×10⁻³ m forl-leucine. The specificities of the transport systems are overlapping but there emerges a wide-affinity transport system for glycine, alanine, leucine, methionine, serine, cysteine, phenylalanine, aspartic acid, asparagine, glutamic acid and tryptophan (and possibly for other amino acids), and more specific systems for each of the following: glycine, lysine, methionine, histidine, arginine, and aspartic and glutamic acids. Proline had the peculiar effect of stimulating the transport of all the amino acids tested. The amino acids apparently interacted in the uptake not only by competition for the binding site but also by allotopic inhibition (e.g.l-cysteine) and possibly stimulation (l-proline). The initial rate of uptake of amino acids and their steady-state level of distribution were characterized by identical activation energies: 7.5 kcal/mole forl-lysine, 6.9 kcal/mole forl-aspartic acid, and 13.2 kcal/mole for glycine.     

Chiral resolution of phenylalanine by d-Phe imprinted membrane considering rejection property

An enantio-selective d-Phe imprinted P(AA-co-AN) membrane was prepared using the wet-phase inversion method. The membrane not only selectively adsorbed phenylalanine but also rejected it with a rejection selectivity of 0.82–0.64 and 0.91–0.63 during the filtration of 100 and 10 ppm (g m⁻³) racemate solutions, respectively. The fluxes of d-Phe and l-Phe during filtration of 10 ppm racemate solution were 0.0077–0.0229 and 0.0064–0.0208 mg m⁻² s⁻¹, respectively, and the fluxes of d-Phe and l-Phe during filtration of 100 ppm racemate solution were 0.1287–0.2522 and 0.1174–0.2458 mg m⁻² s⁻¹, respectively. The adsorption selectivity was higher at low concentration. The adsorption selectivities varied from 1.11 to 1.65 and from 1.64 to 2.78 during filtration of 100 and 10 ppm racemate solutions, respectively. In respect to desorption, the fractional difference between d-Phe and l-Phe in the recovered solution from 10 ppm was higher than that from 100 ppm.     

Regeneration and large-scale propagation of bamboo (Dendrocalamus strictus Nees) through somatic embryogenesis

A complete protocol for large-scale propagation of Dendrocalamus strictus Nees by somatic embryogenesis has been developed. Seeds cultured on agar-solidified Murashige and Skoog (MS) medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D; 3×10^–5 m) produced embryogenic callus from proliferation of the embryo. Somatic embryos formed in vitro multiplied rapidly (two- to five fold every 5 weeks) on semi-solid MS medium containing 2,4-D (1×10^–5 m), kinetin (Kn) (5×10^–6 m), 1-indolebutyric acid (IBA) (2×10^–6 m) and soluble polyvinylpyrrolidone (PVP) (250 mg l^–1), or MS with 2,4-D (1×10^–5 m), 6-benzylaminopurine (BAP) (1×10^–5 m), and soluble PVP (250 mg l^–1). Upon transfer to MS containing 1-naphthaleneacetic acid (NAA) (5×10^–6 m), Kn (5×10^–6 m) and soluble PVP (250 mg l^–1), the dark-green embryos developed into healthy plantlets. Unrooted shoots, if any, obtained on the multiplication media were rooted on MS major salts reduced to half strength supplemented with NAA (3×10^–6 m) and IBA (2.5×10^–6 m). The rooted plants were successfully transferred to soil in polythene bags with over 80% survival. Using this methodology, more than 100,000 plants have been produced. Received: 16 April 1998 / Revision received: 25 September 1998 / Accepted: 10 October 1998     

Regio- and Stereo-selective Hydroxylation of Abietic Acid Derivatives by Mucor circinelloides and Mortierella isabellina

Mucor circinelloides and Mortierella isabellina hydroxylated dehydroabietic acid (DehA). DehA was converted regio- and stereo-selectively by whole cells of Mr. circinelloides to give 2α-hydroxydehydroabietic acid in a 75% molar conversion yield (11 mM from 14.7 mM DehA) after 72 h in the cultivation medium containing 3% (v/v) Tween 80. With cells of Ma. isabellina, under the same conditions, 20.5 mM (6.5 g l⁻¹) 2–hydroxydehydroabietic acid (α/β=81/19) was formed from 26.4 mM DehA.     

Rhamnose lipids – biosynthesis, microbial production and application potential

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⁻¹h⁻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     

Regulation of Cell Volume by β2-adrenergic Stimulation in Rat Fetal Distal Lung Epithelial Cells

Cell-volume changes induced by terbutaline (a specific β₂-agonist) were studied morphometrically in rat fetal distal lung epithelium (FDLE) cells. Cell-volume changes qualitatively differed with the concentration of terbutaline. Terbutaline of 10⁻¹⁰–10⁻⁸ m induced transient cell swelling. Terbutaline of 10⁻⁷ m induced transient cell swelling followed by slow cell shrinkage. Terbutaline of 10⁻⁶–10⁻⁵ m induced rapid cell shrinkage followed by slow cell shrinkage. Terbutaline of 10⁻³ m induced transient cell shrinkage; then cell volume oscillated during stimulation. Benzamil of 10⁻⁶ m suppressed the cell swelling induced by 10⁻¹⁰–10⁻⁸ m terbutaline and quinine of 10⁻³ m inhibited the cell shrinkage induced by 10⁻⁶–10⁻⁵ m terbutaline. These results suggest that cell swelling would be induced by NaCl influx and the cell shrinkage is by KCl efflux. Dibutyryl cyclic AMP (DBcAMP) also induced similar cell-volume changes over a wide range of concentrations (10⁻⁹–10⁻³ m): a low concentration induced transient cell swelling; a high concentration, rapid and slow cell shrinkage. Forskolin (10⁻⁴ m), like terbutaline (10⁻⁵ m), induced rapid cell shrinkage followed by slow cell shrinkage, and this decrease in the cell volume was enhanced by the presence of benzamil. On the other hand, cell shrinkage was induced by ionomycin (even low concentration; 3 × 10⁻¹⁰ m ionomycin), and after that cell volume remained at a plateau level. Removal of extracellular Ca²⁺ abolished the cell swelling caused by terbutaline of 10⁻¹⁰–10⁻⁸ m. With removal of extracellular Ca²⁺, the initial, rapid cell shrinkage induced by 10⁻⁵ m terbutaline became transient, but we still detected slow cell shrinkage similar to that in the presence of extracellular Ca²⁺. Overall, at low concentrations (10⁻¹⁰–10⁻⁸ m), terbutaline induced benzamil-sensitive cell swelling in FDLE cells, which was cAMP- and Ca²⁺-dependent; high concentrations (≥⁻⁶) induced quinine-sensitive rapid cell shrinkage, which was Ca²⁺-dependent; high concentrations (≥⁻⁷) induced slow cell shrinkage, which was cAMP-dependent. These findings suggest that terbutaline regulates cell volume in FDLE cells by cytosolic cAMP and Ca²⁺ through activation of Na⁺ and K⁺ channels. Received: 13 March 1995/Revised: 17 January 1996     

l-Arginine Effects on Na+ Transport in M-1 Mouse Cortical Collecting Duct Cells—A Cationic Amino Acid Absorbing Epithelium

The effect of l-arginine on transepithelial ion transport was examined in cultured M-1 mouse renal cortical collecting duct (CCD) cells using continuous short circuit current (I _SC ) measurements in HCO₃ ⁻/CO₂ buffered solution. Steady state I _SC averaged 73.8 ± 3.2 μA/cm² (n= 126) and was reduced by 94 ± 0.6% (n= 16) by the apical addition of 100 μm amiloride. This confirms that the predominant electrogenic ion transport in M-1 cells is Na⁺ absorption via the epithelial sodium channel (ENaC). Experiments using the cationic amino acid l-lysine (radiolabeled) as a stable arginine analogue show that the combined activity of an apical system y⁺ and a basal amino acid transport system y⁺L are responsible for most cationic amino acid transport across M-1 cells. Together they generate net absorptive cationic amino acid flux. Application of l-arginine (10 mm) either apically or basolaterally induced a transient peak increase in I _SC averaging 36.6 ± 5.4 μA/cm² (n= 19) and 32.0 ± 7.2 μA/cm² (n= 8), respectively. The response was preserved in the absence of bath Cl⁻ (n= 4), but was abolished either in the absence of apical Na⁺ (n= 4) or by apical addition of 100 μm amiloride (n= 6). l-lysine, which cannot serve as a precursor of NO, caused a response similar to that of l-arginine (n= 4); neither L-NMMA (100 μm; n= 3) nor L-NAME (1 mm; n= 4) (both NO-synthase inhibitors) affected the I _SC response to l-arginine. The effects of arginine or lysine were replicated by alkalinization that mimicked the transient alkalinization of the bath solution upon addition of these amino acids. We conclude that in M-1 cells l-arginine stimulates Na⁺ absorption via a pH-dependent, but NO-independent mechanism. The observed net cationic amino acid absorption will counteract passive cationic amino acid leak into the CCD in the presence of electrogenic Na⁺ transport, consistent with reports of stimulated expression of Na⁺ and cationic amino acid transporters by aldosterone. Received: 11 September 2000/Revised: 6 December 2000     

Production of <Emphasis Type="SmallCaps">l</Emphasis>-phenylalanine from glycerol by a recombinant <Emphasis Type="Italic">Escherichia coli</Emphasis>

The production of l-phenylalanine is conventionally carried out by fermentations that use glucose or sucrose as the carbon source. This work reports on the use of glycerol as an inexpensive and abundant sole carbon source for producing l-phenylalanine using the genetically modified bacterium Escherichia coli BL21(DE3). Fermentations were carried out at 37°C, pH 7.4, using a defined medium in a stirred tank bioreactor at various intensities of impeller agitation speeds (300–500 rpm corresponding to 0.97–1.62 m s⁻¹ impeller tip speed) and aeration rates (2–8 L min⁻¹, or 1–4 vvm). This highly aerobic fermentation required a good supply of oxygen, but intense agitation (impeller tip speed ~1.62 m s⁻¹) reduced the biomass and l-phenylalanine productivity, possibly because of shear sensitivity of the recombinant bacterium. Production of l-phenylalanine was apparently strongly associated with growth. Under the best operating conditions (1.30 m s⁻¹ impeller tip speed, 4 vvm aeration rate), the yield of l-phenylalanine on glycerol was 0.58 g g⁻¹, or more than twice the best yield attainable on sucrose (0.25 g g⁻¹). In the best case, the peak concentration of l-phenylalanine was 5.6 g L⁻¹, or comparable to values attained in batch fermentations that use glucose or sucrose. The use of glycerol for the commercial production of l-phenylalanine with E. coli BL21(DE3) has the potential to substantially reduce the cost of production compared to sucrose- and glucose-based fermentations.     

Litre-scale microbial fuel cells operated in a complete loop

Using the anode effluent to compensate the alkalinization in a bio-cathode has recently been proposed as a way to operate a microbial fuel cell (MFC) in a continuous and pH neutral way. In this research, we successfully demonstrated that the operation of a MFC without any pH adjustments is possible by completing the liquid loop over cathode and anode. During the complete loop operation, a stable current production of 23.2 ± 2.5 A m⁻³ MFC was obtained, even in the presence of 3.2–5.2 mg O₂ L⁻¹ in the anode. The use of current collectors and subdivided electrical circuitries for relative large 2.5-L-scale MFCs resulted in ohmic cell resistances in the order of 1.4–1.7 mΩ m³ MFC, which were comparable to values of ten times smaller MFCs. Nevertheless, the bio-cathode activity still needs to be improved significantly with a factor 10–50 in order achieve desirable current densities of 1,000 A m⁻³ MFC. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Amino acid transport inRhodotorula glutinis

The yeastRhodotorula glutinis was found to transport amino acids against a concentration gradient (100∶1 for 10⁻⁶ m l-lysine and 1500∶1 for 10⁻⁶ m α-aminoisobutyric acid). Anaerobically, the concentration gradients of free amino acids were occasionally higher than aerobically. The influx is saturable with an apparentK _m of 1mm forl-lysine and 2mm for α-aminoisobutyric acid. The pH optimum for AIB uptake was 5.0, the apparent activation energy between 5° and 30° was 13,200 cal/mole. Competition of an asymmetric nature among various amino acids for uptake was observed. Intracellular amino acids did not leave the cell under any conditions of incubation, short of breaking up the plasma membrane, but they showed a powerful “trans” inhibitory effect on the uptake of amino acids.     

Chloride Currents Activated by Calcitonin and cAMP in Primary Cultures of Rabbit Distal Convoluted Tubule

Chloride (Cl⁻) conductances were studied in primary cultures of the bright part of rabbit distal convoluted tubule (DCTb) by the whole cell patch clamp technique. The bath solution (33°C) contained (in mm): 140 NaCl, 1 CaCl₂, 10 N-2-hydroxy-ethylpiperazine-N′-2-ethanesulfonic acid (HEPES), pH 7.4 and the pipette solution 140 N-methyl-d-glucamine (NMDG)-Cl, 5 MgATP, 1 ethylene-glycol-bis(b-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), 10 HEPES, pH 7.4. We identified a Cl⁻ current activated by 10⁻⁵ m forskolin, 10⁻³ m 8-bromo adenosine 3′,5′-cyclic monophophosphate (8 Br-cAMP), 10⁻⁶ m phorbol 12-myristate 13-acetate (PMA), 10⁻³ m intracellular adenosine 3′,5′-cyclic monophophosphate (cAMP) and 10⁻⁷ m calcitonin. The current-voltage relationship was linear and the relative ion selectivity was Br⁻ > Cl⁻≫ I⁻ > glutamate. This current was inhibited by 10⁻³ m diphenylamine-2-carboxylate (DPC) and 10⁻⁴ m 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) and was insensitive to 10⁻³ m 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS). These characteristics are similar to those described for the cystic fibrosis transmembrane conductance regulator (CFTR) Cl⁻ conductance. In a few cases, forskolin and calcitonin induced an outwardly rectifying Cl⁻ current blocked by DIDS. To determine the exact location of the Cl⁻ conductance 6-methoxy-1-(3-sulfonatopropyl) quinolinium (SPQ) fluorescence experiments were carried out. Cultures seeded on collagen-coated permeable filters were loaded overnight with 5 mm SPQ and the emitted fluorescence analyzed by laser-scan cytometry. Cl⁻ removal from the apical solution induced a Cl⁻ efflux which was stimulated by 10⁻⁵ m forskolin, 10⁻⁷ calcitonin and inhibited by 10⁻⁵ m NPPB. In 140 mm NaBr, forskolin stimulated an apical Br⁻ influx through the Cl⁻ pathway. Forskolin and calcitonin had no effect on the basolateral Cl⁻ permeability. Thus in DCTb cultured cells, exposure to calcitonin activates a Cl⁻ conductance in the apical membrane through a cAMP-dependent mechanism. Received: 5 July 1995/Revised: 21 December 1995     

Regeneration of Syngonium podophyllum ‘Variegatum’ through direct somatic embryogenesis

A simple and effective method of regenerating Syngonium podophyllum ‘Variegatum’ via direct somatic embryogenesis has been established. Leaf and petiole explants were cultured on Murashige and Skoog (MS) medium supplemented with N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU) or N-phenyl-N′-1,2,3-thiadiazol-5-ylurea (TDZ) with either α-naphthalene acetic acid (NAA) or 2,4-dichlorophenoxyacetic acid (2,4-D). Somatic embryos directly formed at one or two sides of petiole explants on MS medium supplemented 2.5 mg l⁻¹ TDZ with 0.5 mg l⁻¹ NAA or 2.0 mg l⁻¹ TDZ with 0.2 mg l⁻¹ NAA or with 0.2 and 0.5 mg l⁻¹ 2,4-D, respectively. The frequency of petiole explants with somatic embryos produced was as high as 86% when cultured on medium containing 2.5 mg l⁻¹ TDZ with 0.5 mg l⁻¹ NAA. Up to 85% of somatic embryos were able to germinate after transferring onto medium containing 2.0 mg l⁻¹ 6-benzylaminopurine (BA) and 0.2 mg l⁻¹ NAA. Approximately 50–150 plantlets were regenerated from a single petiole explant. However, there was no somatic embryo formation from leaf explants regardless of growth regulator combinations used. Regenerated plantlets from petiole explants were stable and grew vigorously after transplanting to a soilless container substrate in a shaded greenhouse.     

Isolation of <Emphasis Type="Italic">Aspergillus oryzae</Emphasis> mutants for heterologous protein production from a double proteinase gene disruptant

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.     

Regulation of metabolite production by precursors and elicitors in liquid cultures of <Emphasis Type="Italic">Hypericum perforatum</Emphasis>

Four precursors (l-phenylalanine, l-tryptophan, cinnamic acid and emodin) and one signal elicitor (methyl jasmonate, MeJA) were added to liquid cultures of Hypericum perforatum L. to study their effect on production of hyperforin and hypericins (pseudohypericin and hypericin). The addition of l-phenylalanine (75 to 100 mg l⁻¹) enhanced production of hypericins, but hyperforin levels were decreased. Hypericin, pseudohypericin and hyperforin concentrations were all decreased when l-tryptophan (25 to 100 mg l⁻¹) was added to the medium. However, addition of l-tryptophan (50 mg l⁻¹) with MeJA (100 μM) stimulated hyperforin production significantly (1.81-fold) and resulted in an increased biomass. Cinnamic acid (25, 50 mg l⁻¹) and emodin (1.0 to 10.0 mg l⁻¹) each enhanced hyperforin accumulation in H. perforatum, but did not affect accumulation of hypericins.     

Influence of auxins on growth ofClaviceps purpurea (Fries) tulasne in saprophytic cultures

A 10⁻³ m β-indolebutyric and 2,4-dichlorophenoxyacetic acid concentration stimulated the fresh weight increase and dry matter production in the mycelium of staticClaviceps purpurea cultures to 170–180% of the control value. Higher concentrations severely inhibited growth. α-Naphthylacetic acid was less active. β-Indoleacetic acid differed markedly from the other auxins, as it stimulated the fresh weight increase, but at the same time inhibited dry matter production. In submerse cultivation, the differences between the test auxins disappeared; none of them stimulated growth and only inhibition of growth, by concentrations of over 10⁻⁵–10⁻⁴ m, was observed. The used strain did not produce alkaloids in saprophytic cultures, even in the presence of auxins.     

<Emphasis Type="SmallCaps">l</Emphasis>-Proline nutrition and catabolism in <Emphasis Type="Italic">Staphylococcus saprophyticus</Emphasis>

Staphylococcus saprophyticus strains ATCC 15305, ATCC 35552, and ATCC 49907 were found to require l-proline but not l-arginine for growth in a defined culture medium. All three strains could utilize l-ornithine as a proline source and contained l-ornithine aminotransferase and Δ¹-pyrroline-5-carboxylate reductase activities; strains ATCC 35552 and ATCC 49907 could use l-arginine as a proline source and had l-arginase activity. The proline requirement also could be met by l-prolinamide, l-proline methyl ester, and the dipeptides l-alanyl-l-proline and l-leucyl-l-proline. The bacteria exhibited l-proline degradative activity as measured by the formation of Δ¹-pyrroline-5-carboxylate. The specific activity of proline degradation was not affected by addition of l-proline or NaCl but was highest in strain ATCC 49907 after growth in Mueller–Hinton broth. A membrane fraction from this strain had l-proline dehydrogenase activity as detected both by reaction of Δ¹-pyrroline-5-carboxylate with 2-aminobenzaldehyde (0.79 nmol min⁻¹ mg⁻¹) and by the proline-dependent reduction of p-iodonitrotetrazolium (20.1 nmol min⁻¹ mg⁻¹). A soluble fraction from this strain had Δ¹-pyrroline-5-carboxylate dehydrogenase activity (88.8 nmol min⁻¹ mg⁻¹) as determined by the NAD⁺-dependent oxidation of dl-Δ¹-pyrroline-5-carboxylate. Addition of l-proline to several culture media did not increase the growth rate or final yield of bacteria but did stimulate growth during osmotic stress. When grown with l-ornithine as the proline source, S. saprophyticus was most susceptible to the proline analogues L-azetidine-2-carboylate, 3,4-dehydro-dl-proline, dl-thiazolidine-2-carboxylate, and l-thiazolidine-4-carboxylate. These results indicate that proline uptake and metabolism may be a potential target of antimicrobial therapy for this organism.     

Olfactory sensitivity to amino acids in the blackspot sea bream (<Emphasis Type="Italic">Pagellus bogaraveo</Emphasis>): a comparison between olfactory receptor recording techniques in seawater

The current study investigated the olfactory sensitivity of the blackspot sea bream to amino acids, odorants associated with food detection in fish, and compared the efficacy of two different experimental methods: multi-unit recording from the olfactory nerve and the electro-olfactogram (EOG). Twenty essential amino acids plus l-DOPA evoked clear, concentration-dependent olfactory responses using both methods, with estimated thresholds of 10^−8.5–10^−6.2 M (nerve recording) and 10^−7.5–10^−4.8 M (EOG). The most potent amino acids were l-cysteine, l-methionine (both sulphur-containing), l-alanine, l-leucine (both neutral), l-glutamine (amide-containing) and l-serine (hydroxyl-containing). The least potent were l-proline (secondary α-amino group), the aromatic amino acids and glycine (simplest). Although the rank order of olfactory potency was similar for the two methods used, and the calculated thresholds given by the two methods were positively correlated, the sensitivity of the EOG was consistently lower than multi-unit recording by approximately one order of magnitude, presumably due to the electrical shunting effect of seawater. As in freshwater, the EOG could be a valid method for comparing olfactory potency of different odorants in stenohaline marine fish; however, for absolute ‘biological’ thresholds, a more invasive recording technique, such as multi-unit recording from the olfactory nerve, should be used.     

Histidine Absorption across Apical Surfaces of Freshwater Rainbow Trout Intestine: Mechanistic Characterization and the Influence of Copper

The essential amino acid histidine performs critical roles in health and disease. These functions are generally attributed to the amino acid itself, but could also be mediated by a positive effect on trace element bioavailability. Mechanistic information regarding the absorption of histidine across the gastrointestinal tract is essential for understanding the interplay between amino acid and mineral nutrients and the implications of these interactions for nutrition and toxicology. Using intestinal brush-border membrane vesicles obtained from freshwater rainbow trout, absorption of histidine over the range 0.78–780 μm was found to be saturable, with a maximal transport rate (J _max) of 9.1 ± 0.8 nmol mg protein⁻¹ min⁻¹ and a K _m (histidine concentration required to reach 50% of this level) of 339 ± 68 μm. Histidine uptake was highly specific as 10-fold elevated levels of a variety of amino acids with putative shared transporters failed to significantly inhibit uptake. Elevated levels of d-histidine, however, impaired uptake of the natural l-isomer. The presence of “luminal” copper (8.3 μm) significantly increased both the J _max and K _m of histidine transport. This suggests that chelated copper–histidine species cross the brush-border epithelium through transport pathways distinct from those used by histidine alone.     

A Novel,Volume-correlated Cl− Conductance in Marginal Cells Dissociated from the Stria Vascularis of Gerbils

Using the whole-cell patch-clamp technique, we examined Cl⁻-selective currents manifested by strial marginal cells isolated from the inner ear of gerbils. A large Cl⁻-selective conductance of ∼18 nS/pF was found from nonswollen cells in isotonic buffer containing 150 mm Cl⁻. Under a quasi-symmetrical Cl⁻ condition, the `instantaneous' current-voltage relation was close to linear, while the current-voltage relation obtained at the end of command pulses of duration 400 msec showed weak outward rectification. The permeability sequence for anionic currents was as SCN⁻ > Br⁻≅ Cl⁻ > F⁻ > NO⁻ ₃≅ I⁻ > gluconate⁻, corresponding to Eisenmann's sequence V. When whole-cell voltage clamped in isotonic bathing solutions, the cells exhibited volume changes that were accounted for by the Cl⁻ currents driven by the imposed electrochemical potential gradients. The volume change was elicited by lowered extracellular Cl⁻ concentration, anion substitution and altered holding potentials. The Cl⁻ conductance varied in parallel with cell volume when challenged by bath anisotonicity. The whole-cell Cl⁻ current was only partially blocked by both 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB, 0.5 mm) and diphenylamine-2-carboxylic acid (DPC, 1.0 mm), but 4-acetamido-4′-isothiocyanato-stilbene-2,2′-disulfonic acid (SITS, 0.5 mm) was without effect. The properties of the present whole-cell Cl⁻ current resembled those of the single Cl⁻ channel previously found in the basolateral membrane of the marginal cell (Takeuchi et al., Hearing Res. 83:89–100, 1995), suggesting that the volume-correlated Cl⁻ conductance could be ascribed predominantly to the basolateral membrane. This Cl⁻ conductance may function not only in cell volume regulation but also for the transport of Cl⁻ and the setting of membrane potential in marginal cells under physiological conditions. Received: 15 August 1995/Revised: 3 November 1995     

Taxane Production in Suspension Culture of <Emphasis Type="Italic">Taxus</Emphasis> × <Emphasis Type="Italic">Media</Emphasis> var. <Emphasis Type="Italic">Hicksii</Emphasis> Carried Out in Flasks and Bioreactor

Paclitaxel and 10-deacetylbaccatin III (10-DAB III) were produced in suspension cultures of Taxus × media var. Hicksii grown in shake-flasks and in a 7-l bioreactor reaching, in the bioreactor, 4.4 mg l⁻¹ (on day 14) and 37.5 mg l⁻¹ (on day 11). In shake-flasks the highest total content of paclitaxel and 10-DAB III was 7.3 mg l⁻¹ (on day 4) and 8.8 mg l⁻¹ (on day 18). Phenylalanine, at 0.05 mM, increased paclitaxel accumulation in cells cultivated in bioreactor and flasks 30-fold and 9-fold (from 0.02 mg l⁻¹ to 0.6 mg l⁻¹ and to 0.2 mg l⁻¹, respectively). The 10-DAB III content in cells from flasks was increased from 0.4 mg l⁻¹ to 1.6 mg l⁻¹.