The use of various substrates and substrate concentrations by a Hyphomicrobium sp. isolated from soil: Effect on growth rate and growth yield

The content of Hyphomicrobium sp. was estimated from a clay loam soil using the most probable number technique with methanol as the sole carbon source. The method enumerated Hyphomicrobia as 0.2% of the total bacteria determined by acridine orange direct counts. Hyphomicrobium sp. was not able to use C-C compounds such as glucose or acetate for growth. Maximal growth yield and growth rate were obtained when the concentration of methanol was in the range of 0.5–5 mg C/liter. Substrate affinity measurements revealed K_s values of 0.8 m and 5.8 m when the methanol concentration was 0.5–2.5 m and 5–200 m, respectively. Hyphomicrobium sp. had the ability to assimilate volatile organic compounds from air for growth. A growth yield of 0.7 mg/liter cell carbon was obtained in a mineral medium that contained no additions of organic compounds but had been stored for 4 weeks in flasks, allowing volatile compounds from the air to dissolve in the medium. When air was pumped into the culture during cultivating, the growth yield was proportional to the flow rate of air into the culture. Correspondence to: Kari Aa     

Partial purification and characterization of β-hydroxybutyric acid dehydrogenase of a methylotrophic bacterium,Pseudomonas 135

Summary An intracellular enzyme, d(—)--hydroxybutyric acid dehydrogenase involved in an intracellular poly-d(—)--hydroxybutyric acid degredation was isolated from a facultative methylotrophic bacterium, Pseudomonas 135, grown on methanol as a sole carbon and energy source. This enzyme was partially purified to 11.6-fold by ammonium sulphate fractionation and a dye-affinity chromatography. The enzyme catalysed simultaneously the oxidation of d(—)--hydroxybutyric acid (D-HB) and the reduction of acetoacetate. The optimum pH was 8.5 for the oxidation reaction and 5.5–6.0 for the reduction reaction, and the enzyme was stable for 2 weeks at — 20° C. The K _m values for oxidation and reduction reactions were determined as 1.84 mm for D-HB, 0.244 mm for NAD⁺, 0.319 mm for acetoacetate and 0.032 mm for NADH, respectively. It was also found that d-lactate and NADH significantly inhibited the oxidation reaction by competitive inhibition, and acetoacetate by non-competitive inhibition, respectively. The inhibition constants were determined as 1.49 mm for d-lactate, 0.196 mm for NADH and 1.82 mm for acetoacetate, respectively. According to an experiment with resting cells, it seemed that the enzyme was constitutive. Correspondence to: J. M. Lebeault     

Excretion of photosynthetically fixed organic carbon by metalimnetic phytoplankton

The effects of light intensity, oxygen concentration, and pH on the rates of photosynthesis and net excretion by metalimnetic phytoplankton populations of Little Crooked Lake, Indiana, were studied. Photosynthetic rates increased from 1.42 to 3.14 mg C·mg^–1 chlorophylla·hour^–1 within a range of light intensities from 65 to 150E·m^–2·sec^–1, whereas net excretion remained constant at 0.05 mg C·mg^–1 chlorophylla·hour^–1. Bacteria assimilated approximately 50% of the carbon released by the phytoplankton under these conditions. Excreted carbon (organic compounds either assimilated by bacteria or dissolved in the lake water) was produced by phytoplankton at rates of 0.02–0.15 mg C·mg^–1 chlorophylla·hour^–1. These rates were 6%–13% of the photosynthetic rates of the phytoplankton. Both total excretion of carbon and bacterial assimilation of excreted carbon increased at high light intensities whereas net excretion remained fairly constant. Elevated oxygen concentrations in samples incubated at 150E· m^–2·sec^–1 decreased rates of both photosynthesis and net excretion. The photosynthetic rate increased from 3.0 to 5.0 mg C·mg^–1 chlorophylla· hour^–1 as the pH was raised from 7.5 to 8.8. Net excretion within this range decreased slightly. Calculation of total primary production using a numerical model showed that whereas 225.8 g C·m^–2 was photosynthetically fixed between 12 May and 24 August 1982, a maximum of about 9.3 g C·m^–2 was released extracellularly.     

Aerobic nitrate and nitrite reduction in continuous cultures of Escherichia coli E4

Nitrate and nitrite was reduced by Escherichia coli E4 in a l-lactate (5 mM) limited culture in a chemostat operated at dissolved oxygen concentrations corresponding to 90–100% air saturation. Nitrate reductase and nitrite reductase activity was regulated by the growth rate, and oxygen and nitrate concentrations. At a low growth rate (0.11 h^–1) nitrate and nitrite reductase activities of 200 nmol · mg^–1 protein · min^–1 and 250 nmol · mg^–1 protein · min^–1 were measured, respectively. At a high growth rate (0.55 h^–1) both enzyme activities were considerably lower (25 and 12 nmol mg^–1 · protein · min^–1). The steady state nitrite concentration in the chemostat was controlled by the combined action of the nitrate and nitrite reductase. Both nitrate and nitrite reductase activity were inversely proportional to the growth rate. The nitrite reductase activity decreased faster with growth rate than the nitrate reductase. The chemostat biomass concentration of E. coli E4, with ammonium either solely or combined with nitrate as a source of nitrogen, remained constant throughout all growth rates and was not affected by nitrite concentrations. Contrary to batch, E. coli E4 was able to grow in continuous cultures on nitrate as the sole source of nitrogen. When cultivated with nitrate as the sole source of nitrogen the chemostat biomass concentration is related to the activity of nitrate and nitrite reductase and hence, inversely proportional to growth rate.     

Heterotrophic growth of Thiobacillus acidophilus in batch and chemostat cultures

Heterotrophic growth of the facultatively chemolithoautotrophic acidophile Thiobacillus acidophilus was studied in batch cultures and in carbon-limited chemostat cultures. The spectrum of carbon sources supporting heterotrophic growth in batch cultures was limited to a number of sugars and some other simple organic compounds. In addition to ammonium salts and urea, a number of amino acids could be used as nitrogen sources. Pyruvate served as a sole source of carbon and energy in chemostat cultures, but not in batch cultures. Apparently the low residual concentrations in the steady-state chemostat cultures prevented substrate inhibition that already was observed at 150 M pyruvate. Molar growth yields of T. acidophilus in heterotrophic chemostat cultures were low. The Y _max and maintenance coefficient of T. acidophilus grown under glucose limitation were 69 g biomass · mol^–1 and 0.10 mmol · g^–1 · h^–1, respectively. Neither the Y _max nor the maintenance coefficient of glucose-limited chemostat cultures changed when the culture pH was increased from 3.0 to 4.3. This indicates that in T. acidophilus the maintenance of a large pH gradient is not a major energy-requiring process. Significant activities of ribulose-1,5-bisphosphate carboxylase were retained during heterotrophic growth on a variety of carbon sources, even under conditions of substrate excess. Also thiosulphate- and tetrathionate-oxidising activities were expressed under heterotrophic growth conditions.     

Living cell reaction process forl-isoleucine andl-valine production

Summary A new process (Living Cell Reaction Process) forl-isoleucine production using viable, non-growing cells ofBrevibacterium flavum AB-07 was optimised using ethanol as the energy source and -ketobutyric acid (-KB) as precursor.l-valine also could be produced from glucose at high yield by this process. This process differs from the usual fermentation method in that non-growing cells are used, and the production ofl-isoleucine andl-valine were carried out under conditions of repressed cell division and growth. Minimal medium missing the essential growth factor, biotin was employed as the reaction mixture for the production ofl-isoleucine andl-valine. The productivity ofl-isoleucine andl-valine were 200 mmol·l^–1 · day^–1 (molecular yield to -KB: 95%) and 300 mmol · l^–1 · day^–1 (molecular yield to glucose: 80%) respectively. The content ofl-isoleucine andl-valine in total amino acids produced in the each mixture were 97% and 96% respectively.     

High efficiency styrene biodegradation in a biphasic organic/water continuous reactor

Styrene was degraded as sole source of carbon and energy by a selected bacterial community in a two-phase aqueous-organic medium (80%:20%, vol/vol). Silicone oil was used to solubilize styrene, which is sparingly soluble in water and to prevent its toxicity toward microorganisms. Preliminary studies with the mixed population in batch cultures indicate that the specific activity and the maximum growth rate at optimal 3H 6.0 were 46 mg·g^–1·h^–1 and 0.15 h^–1, respectively. In pH-regulated chemostat cultures, styrene was degraded at dilution rates ranging from 0.05 to 0.20 h^–1. Kinetic parameters and the proportion of each strain in the mixed culture were followed. At 0.20 h^–1, only one strain as compared to four initially present, remained in the medium. This strain Pseudomonas aeruginosa, degrades styrene with a specific activity of 293 mg·g^–1·h^–1. Such results could lead to industrial treatment of waste gas or water polluted with styrene. Correspondence to: J,-M. Lebeault     

Transport of monoamine and amino acid neurotransmitters by primary astroglial cultures

The transport of [³H]l-glutamate, [³H]l-aspartate, [³H]-aminobutyric acid ([³H]GABA), [³H]dopamine, [³H]norepinephrine and [³H]5-hydroxytryptamine (³H-5-HT) was measured in primary astroglial cultures from newborn rat cerebral hemispheres. There was a high-affinity uptake with aK _m of 69.0 M for L-glutamate, 12.3 M forl-aspartate and 3.1 M for GABA. The uptake showed properties of high capacity with aV _max of 17.0 nmol·mg prot^–1·min^–1 forl-glutamate, 1.1 nmol·mg prot^–1·min^–1 forl-aspartate and 0.04 nmol·mg prot^–1·min^–1 for GABA. No high-affinity high capacity transport system was found for the monoamines studies. Autoradiographic examination demonstrated a heavy deposit of grains suggesting a prominent accumulation of [³H]l-glutamate and [³H]l-aspartate in the astroglial-like cells of the cultures, while the [³H]GABA accumulation was less intense. On the other hand, there was only a weak accumulation of grains after incubating the cultures with [³H]dopamine, [³H]norepinephrine or [³H]5-HT. Thus, astroglial cells in culture accumulate amino acid neurotransmitters and monoamines in different ways with a high-affinity high-capacity uptake of glutamate, aspartate and GABA and a diffusion-uptake of dopamine, norepinephrine and 5-HT.     

Light response of D1 turnover and photosystem II efficiency in the seagrassZostera capricorni

Biochemical and biophysical parameters, including D1-protein turnover, chlorophyll fluorescence, oxygen evolution activity and zeaxanthin formation were measured in the marine seagrassZostera capricorni (Aschers) in response to limiting (100 mol·m^–2·^–1), saturating (350 mol·m^–2·s^–1) or photoinhibitory (1100 mol·m^–2·s^–1) irradiances. Synthesis of D1 was maximal at 350 mol·m^–2·s^–1 which was also the irradiance at which the rate of photosynthetic O₂ evolution was maximal. Degradation of D1 was saturated at 350 mol·m^–2·s^–1. The rate of D1 synthesis at 1100 mol·m^–2·s^–1 was very similar to that at 350 mol·m^–2·s^–1 for the first 90 min but then declined. At limiting or saturating irradiance little change was observed in the ratio of variable to maximal fluorescence (Fv/Fm) measured after dark adaptation of the leaves, while significant photoinhibition occurred at 1100 mol·m^–2·s^–1. The proportion of zeaxanthin in the total xanthophyll pool increased with increasing irradiance, indicative of the presence of a photoprotective xanthophyll cycle in this seagrass. These results are consistent with a high level of regulatory D1 turnover inZostera under non-photoinhibitory irradiance conditions, as has been found previously for terrestrial plants.We would like to thank Professor Peter Böger (Department of Plant Biochemistry, University of Konstanz, Germany) for the kind gift of D1 antibodies. This work was partly supported by a University of Queensland Enabling Grant to CC.     

Biological denitrification of water in a two-chambered immobilized-cell bioreactor

Summary A double-chambered bioreactor based on a composite immobilized-cell gel layer/microporous membrane structure was applied to the continuous denitrification of high-nitrate water. Immobilized denitrifying bacteria (Pseudomonas denitrificans) were provided with separate flows of nitrate and carbon (C) nutrient, with no contamination of the treated water by cell leakage from the gel. Using acetate (7.5 mm) as a C source and a C/N ratio of 3 (mol/mol), specific denitrification rates ranging from 15 to 25 g NO _inf3 ^sup– · h^–1 · – cm^–2 membrane surface (50–85 g NO _inf3 ^sup– · h^–1 · cm^–3 gel) were obtained. The denitrifying activity remained stable for several months. At the flow rate used (10 cm³ · h^–1), the effluents contained noticeable amounts of NO _inf2 ^sup– ions but the treated water remained uncontaminated by the carbon nutrient. Most NO _inf2 ^sup– ions disappeared from the treated water in a second reactor connected in series. When fed with an unchlorinated sludge supernatant as C nutrient, immobilized bacteria performed efficient denitrification of water for only 3 weeks. Diffusion experiments showed that acetate ions diffused much less rapidly than NO _inf3 ^sup– or NO _inf2 ^sup– ions through the composite structure. Further developments of the system are considered.     

Nucleoside transport in mammalian cell membranes

Summary Transport of the nucleoside analog cytosine-arabinoside (CAR) in transformed hamster cells in culture has been studied in conditions of minimal metabolic conversion. Uptake (zero-trans in) properties at 20°C over a limited range of CAR concentrations were characterized by aK _m of 350 m and a maximal velocity (V) of 780 m·min^–1 (V/K _m =2.28 min^–1). Equilibrium exchange at 20°C over a wider range of concentrations was best described by a saturable component with aK _m of 500 m and av of 1230 m·min^–1 (V/K _m =2.26 min^–1) and either a saturable component of highK _m or a nonsaturable component ofk=0.3 min^–1. For the saturable component, thev/K _m values were similar in both procedures.CAR transport was inhibited by various metabolizable nucleosides. Uptake of some of these nucleosides was inhibited by CAR. CAR transport and uridine uptake were inhibited in a reversible but partially competitive fashion by high affinity probes like S-(p-nitrobenzyl-6-mercaptoinosine (NBMI) (K _i <0.5nm) and in an irreversible fashion by SH reagents such as N-ethylmaleiimide (NEM). The organomercurialp-hydroxymercuribenzene sulfonate (pMBS) markedly stimulated transport of these nucleosides, but also markedly potentiated the inhibitory effects of either NBMI or NEM. These effects are interpreted either in terms of models which invoke allosteric properties or in terms of two transport systems which display distinct chemical susceptibilities to externally added probes.     

Mineralization of 3-chloro-4-methylaniline via an ortho-cleavage pathway by Pseudomonas cepacia strain CMA1

Pseudomonas cepacia strain CMA1, which was isolated from soil, utilized 3-chloro-4-methylaniline (3C4MA) in concentrations up to 1.4 mm (0.2 g·l^–1) as the sole source of carbon, nitrogen, and energy. In addition, 3-chloroaniline, 4-chloroaniline and phenol, but not aniline or methylanilines, were degraded by strain CMA1. Biodegradation of the anilines was coupled to the liberation of ammonium and chloride. The broad specificities of the aniline- and catechol-oxidizing enzymes were demonstrated in oxygen uptake experiments, which in addition showed higher activities for ring-cleaving than for aniline-oxidizing enzymes. Two ring-cleaving catechol 1,2-dioxygenases, which were induced selectively after growth on 3C4MA (pyrocatechase type II) and phenol (pyrocatechase type I), respectively, were discerned after partial purification by DEAE-cellulose chromatography. Correspondence to: F. Streichsbier     

Presence of an X AG − carrier in frog (Rana esculenta) red blood cells

Evidence is presented that the high levels of internal l-glutamic and l-aspartic acid in frog Rana esculenta red blood cells are due to the existence of a specific carrier for acidic amino acids of high affinity K _m = 3 m and low capacity (V_max) 0.4 mol l-Glu · Kg^–1 dry cell mass · 10 min^–1. It is Na+ dependent and the incorporation of l-glutamic acid can be inhibited by l and d-aspartate and l-cysteic acid, while d-glutamic does not inhibit. Moreover, this glutamic uptake shows a bell-shaped dependence on the external pH. All these properties show that this carrier belongs to the system X _AG ^– family. Besides the incorporation through this system, l-glutamic acid is also taken up through the ASC system, although, under physiological conditions, this transport is far less important, since it has relatively low affinity K _m 39 m but high capacity (V _max) 1.8 mol l-Glu · Kg^–1 dry cell mass · 10 min^–1.     

Regulation of phospho(enol)-pyruvate-and oxaloacetate-converting enzymes in Corynebacterium glutamicum

The presence and properties of the enzymes involved in the synthesis and conversion of phospho(enol)pyruvate (PEP) and oxaloacetate (OAA), the precursors for aspartate-derived amino acids, were investigated in three different Corynebacterium strains. This study revealed the presence of both PEP carboxykinase 0.29 mol·min^–1·mg^–1 of protein [units (U)·mg^–1] and PEP synthetase (0.13 U·mg^–1) in C. 2 glutamicum as well as pyruvate kinase (1.4 U·mg^–1) and PEP carboxylase (0.16 U·mg^–1). With the exception of PEP carboxykinase these activities were also present in glucose-grown C. flavum and C. lactofermentum. Pyruvate carboxylase activity was not detected in all three species cultivated on glucose or lactate. At least five enzyme activities that utilize OAA as a substrate were detected in crude extracts of C. glutamicum: citrate synthase (2 U·mg^–1), malate dehydrogenase (2.5 U·mg^–1), glutamate: OAA transaminase (1 U·mg^–1), OAA-decarboxylating activity (0.89 U·mg^–1) and the previously mentioned PEP carboxykinase (0.29 U·mg^–1). The partially purified OAA-decarboxylase activity of C. glutamicum was completely dependent on the presence of inosine diphosphate and Mn²⁺, had a Michaelis constant (K _m) of 2.0mm for OAA and was inhibited by ADP and coenzyme A (CoA). Examination of the kinetic properties showed that adenine nucleotides and CoA derivatives have reciprocal but reinforcing effects on the enzymes catalyzing the interconversion of pyruvate, PEP and OAA in C. glutamicum. A model for the regulation of the carbon flow based on these findings is presented.Correspondence to: M. S. M. Jetten     

Continuous chemotrophic growth and respiration of Chromatiaceae species at low oxygen concentrations

Endogenous and maximum respiration rates of nine purple sulfur bacterial strains were determined. Endogenous rates were below 10 nmol O₂ · (mg protein · min)^-1 for sulfur-free cells and 15–35 nmol O₂ · (mg protein · min)^-1 for cells containg intracellular sulfur globules. With sulfide as electron-donating substrate respiration rates were considerably higher than with thiosulfate. Maximum respiration rates of Thiocystis violacea 2711 and Thiorhodovibrio winogradskyi SSP1 (254.8 and 264.2 nmol O₂ · (mg protein · min)^-1, respectively) are similar to those of aerobic bacteria. Biphasic respiration curves were obtained for sulfur-free cells of Thiocystis violacea 2711 and Chromatium vinosum 2811. In Thiocystis violacea the rapid and incomplete oxidation of thiosulfate was five times faster than the oxidation of stored sulfur. A high affinity of the respiratoty system for oxygen (K _m =0.3–0.9 M O₂, V _max=260 nmol O₂ · (mg protein · min)^-1 with sulfide as substrate, K _m =0.6–2.4 M O₂, V _max=14–40 nmol O₂ · (mg protein · min)^-1 with thiosulfate as substrate), for sulfide (K _m =0.47 M, V _max=650 nmol H₂S · (mg protein × min)^-1, and for thiosulfate (K _m =5–6 M, V _max =24–72 nmol S₂O ₃ ^2- · (mg protein · min)^-1 was obtained for different strains. Respiration of Thiocystis violacea was inhibited by very low concentrations of NaCN (K _i =1.7 M) while CO concentrations of up to 300 M were not inhibitory. The capacity for chemotrophic growth of six species was studied in continuous culture at oxygen concentrations of 11 to 67 M. Thiocystis violacea 2711, Amoebobacter roseus 6611, Thiocapsa roseopersicina 6311 and Thiorhodovibrio winogradskyi SSP1 were able to grow chemotrophically with thiosulfate/acetate or sulfide/acetate. Chromatium vinosum 2811 and Amoebobacter purpureus ML1 failed to grow under these conditions. During shift from phototrophic to chemotrophic conditions intracellular sulfur and carbohydrate accumulated transiently inside the cells. During chemotrophic growth bacteriochlorophyll a was below the detection limit.     

Effect of oligomycin on NADH oxidation and its coupled phosphorylation with the particulate fraction from dark aerobically grown Rhodospirillum rubrum

Summary NADH oxidation with the particulate fraction from dark aerobically grown Rhodospirillum rubrum is significantly stimulated by the addition of phosphate (Pi) and Mg⁺⁺, or Pi, Mg⁺⁺, ATP and the hexokinase-glucose system. K _m values for Pi in NADH oxidation and phosphorylation are 10^–3 m and 8×10^–4 m, respectively. These K _m values are almost the same as in corresponding photophosphorylation and oxidative phosphorylation catalyzed with chromatophores. As in the case of NADH oxidation with chromatophores, NADH oxidation with the particulate fraction has an optimal pH at 7.5 without additions, which is shifted to 6.9 by the addition of Pi and Mg⁺⁺, or Pi, Mg⁺⁺, ATP and the hexokinase-glucose system. The optimal pH for coupled phosphorylation is 6.9. 10 g per ml of oligomycin can suppress stimulation of NADH oxidation by Pi, or by the energy trapping system, and prevent the shift of optimal pH. The particulate fraction can catalyze Pi-incorporation into glucose-6-phosphate without externally added ATP, so that Pi-incorporation is inhibited by oligomycin. From these findings, it is concluded that NADH oxidation in the particulate fraction is tightly coupled to phosphorylation.     

Decrease of polypeptides in the PS I antenna complex with increasing growth irradiance in the red alga Porphyridium cruentum

Thylakoids isolated from cells of the red alga Porphyridium cruentum exhibit an increased PS I activity on a chlorophyll basis with increasing growth irradiance, even though the stoichiometry of Photosystems I and II in such cells shows little change (Cunningham et al. (1989) Plant Physiol 91: 1179–1187). PS I activity was 26% greater in thylakoids of cells acclimated at 280 mol photons · m^–2 · s^–1 (VHL) than in cells acclimated at 10 mol photons · m^–2 · s^–1 (LL), indicating a change in the light absorbance capacity of PS I. Upon isolating PS I holocomplexes from VHL cells it was found that they contained 132±9 Chl/P700 while those obtained from LL cells had 165±4 Chl/P700. Examination of the polypeptide composition of PS I holocomplexes on SDS-PAGE showed a notable decrease of three polypeptides (19.5, 21.0 and 22 kDa) in VHL-complexes relative to LL-complexes. These polypeptides belong to a novel LHC I complex, recently discovered in red algae (Wolfe et al. (1994a) Nature 367: 566–568), that lacks Chl b and includes at least six different polypeptides. We suggest that the decrease in PS I Chl antenna size observed with increasing irradiance is attributable to changes occurring in the LHC I-antenna complex. Evidence for a Chl-binding antenna complex associated with PS II core complexes is lacking at this point. LHC II-type polypeptides were not observed in functionally active PS II preparations (Wolfe et al. (1994b) Biochimica Biophysica Acta 1188: 357–366), nor did we detect polypeptides that showed immunocross-reactivity with LHC II specific antisera (made to Chlamydomonas and Euglena LHC II).Abbreviations Bis-Tris bis(2-hydroxyethyl)imino-tris(hydroxymethyl)methane - DCPIP 2,6-dichlorophenol indophenol - -dm dodecyl--d-maltoside - HL high light of 150 mol photons · m^–2 · s^–1 - LGB lower green band - LHC I light-harvesting complex of PS I - LHC II light-harvesting complex of PS II - LL low light of 10 mol photons · m^–2 · s^–1 - ML medium light of 50 mol photons · m^–2 · s^–1 - MES 2-(N-morpholino) ethanesulfonic acid - P700 reaction center of PS I - PFD photon flux density - Trizma tris(hydroxymethyl)aminomethane - UGB upper green band - VHL very high light of 280 mol photons · m^–2 · s^–1     

Kinetic studies on the stimulation of Na+−H+ exchange activity in renal brush border membranes isolated from thyroid hormone-treated rats

Summary Na⁺–H⁺ exchange activity in renal brush border membrane vesicles isolated from hyperthyroid rats was increased. When examined as a function of [Na⁺], treatment altered the initial rate of Na⁺ uptake by increasingV _m (hyperthyroid, 18.9±1.1 nmol Na⁺ · mg^–1 · 2 sec^–1; normal, 8.9±0.3 nmol Na⁺ · mg^–1 · 2 sec^–1), and not the apparent affinityK _Na ⁺ (hyperthyroid, 7.3±1.7mm; normal, 6.5±0.9mm). When examined as a function of [H⁺] and at a subsaturating [Na⁺] (1mm), hyperthyroidism resulted in the proportional increase in Na⁺ uptake at every intravesicular pH measured. A positive cooperative effect on Na⁺ uptake was found with increased intravesicular acidity in vesicles from both normal and hyperthyroid rats. When the data were analyzed by the Hill equation, it was found that hyperthyroidism did not change then (hyperthyroid, 1.2±0.06; normal, 1.2±0.07) or the [H⁺]_0.5 (hyperthyroid, 0.39±0.08 m; normal, 0.44±0.07 m) but increased the apparentV _m (hyperthyroid, 1.68±0.14 nmol Na⁺ · mg^–1 · 2 sec^–1; normal 0.96±0.10 nmol Na⁺ · mg^–1 · 2 sec^–1). The uptake of Na⁺ in exchange for H⁺ in membrane vesicles from normal and hyperthyroid animals was not influenced by membrane potential. H⁺ translocation or debinding was rate limiting for Na⁺–H⁺ exchange since Na⁺–Na⁺ exchange activity was greater than Na⁺–H⁺ exchange activity. Hyperthyroidism caused a proportional increase and hypothyroidism caused a proportional decrease in Na⁺–Na⁺ and Na⁺–H⁺ exchange. We conclude that hyperthyroidism leads to either an increase in the number of functional exchangers in the membrane or exactly proportional increases in the rate-limiting steps for Na⁺–Na⁺ and Na⁺–H⁺ exchange activity.     

Alpha and beta adrenergic agonists stimulate water absorption in the rat proximal tubule

Summary Simultaneous capillary and luminal microperfusion studies were performed in the rat proximal tubule to determine the effects of the beta agonist isoproterenol and the alpha agonist phenylephrine on water absorption. Capillary and luminal perfusion solutions were composed such that organic solutes were not present, no bicarbonate was present in the lumen, and no chloride gradient was imposed. Under such conditions, water absorption (Jv) averaged 0.36±0.11 nl·min^–1·mm^–1. The addition of isoproterenol to the capillary solution in concentrations of 10^–6 and 10^–4 m resulted in significantly higherJv's of 0.68±0.10 and 0.71±0.11 nl·min^–1·mm^–1, respectively. The enhancing effect of isoproterenol was inhibited by the beta blocker propranolol (10^–4 m), but not by the alpha blocker phentolamine (10^–7 m). The addition of phenylephrine (10^–6 m) to the capillary perfusion solution also resulted in a significantly higherJv of 0.84±0.14 nl·min^–1·mm^–1, an effect inhibited by phentolamine (10^–7 m), but not by propranolol (10^–4 m). Neither phentolamine nor propranolol alone in the concentrations indicated had an effect on water absorption. These experiments indicate that both alpha and beta agonists stimulate water absorption in the superficial proximal tubule of the rat. This effect appears to be relatively specific for each class of agonist, as demonstrated by the effects of the specific antagonists.     

Foraminifera and meiofauna on an intertidal mudflat,Cornwall, England: Populations; respiration and secondary production; and energy budget

A rich and varied meiofauna inhabits a Cornish mudflat near the mouth of the Tamar River in southwestern England. Population densities range from 117 to 943 individuals · g^–1 (wet) sediment (1.4–11.4 × 10⁶ individuals · m^–2), with foraminifera, harpacticoid copepods and nematodes appearing in nearly equal numbers and comprising most of the meiofauna. Seasonally, meiofaunal numbers rise and fall with solar radiation and vary inversely with river discharge. Two species, the atestate allogromiid A and the calcareous Haynesina germanica (Ehrenberg), far outnumber other foraminifera; their population densities and growth rates reach maxima in spring and summer.Monthly rates of sediment respiration are locally variable, but clearly increase from winter (4.13 ml O₂ · m^–2 · h^–1 in December) to spring (38.87 ml O₂ · m^–2 · h^–1 in April). Experiments and calculations ascribe approximately 30% of this total to the meiofauna (including microfauna and microflora), 50% to bacteria and less than 20% to chemical oxidation. A tentative energy budget for the mudflat suggests that secondary production by meiofauna is small as compared with coastal environments elsewhere, and that meiofaunal production (426 Kcal · m^–2 · y^–1) is nearly twice meiofaunal respiration (252 Kcal · m^–2 · yr^–1).