Mobility and electric charge of screening pigment granules in the superposition eye ofEphestia kuehniella Z.

Summary The mobility and the electric charge of screening pigment granules of the mealmoth superposition eye were determined electrophoretically in buffer solutions. In potassium phosphate buffer the mobility of the negatively charged granules is linearly dependent on the pH in the range from 4.8 to 7.7 (Fig. 2), and in veronal buffer from pH= 2.3 to pH=7.5 (Fig. 3). At pH=6.6 the values of the effective charge per granule vary between 9.4·10^–17 C and 2.0·10^–16 C, those of the real charge between 2.4·10^–14 C and 5.6·10^–14 C (Table 1, Appendix). For equal electric fields, the mobility of the granules decreases with increasing ionic strength, and it remains the same for > 0.075 mol/1 (Fig. 4).     

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.     

Chloroplast dielectrophoresis

Dielectrophoretic coefficients of chloroplasts, untreated and treated with cationized ferritin, have been measured in axisymmetric ac electric fields at different frequencies. The treated chloroplasts have surface charge density 2.4 times smaller than the untreated ones.The dielectrophoretic coefficients are in the range 10^-25 F · m² to 7x10^-25 F · m² for frequencies from 6,000 Hz to 1 MHz. Dielectrophoretic effects have not been observed for frequencies from 1 to 6,000 Hz and from 1 MHz and 10 MHz. The surface charge decrease leads to an increase of 2–3 times in the dielectrophoretic coefficients and slight shift of the dielectrophoretic mobility of lower frequencies.These results may be qualitatively explained on the basis of the existing theories for cell and vesicle dielectrophoresis.Abbreviations DCMU 3-(3,4-Dichlorophenyl)-1,1-Dymethylurea - EDTA Ethylenediaminetetraacetic acid - HEPES (N-2 Hydroxyethylpiperozine-N-2-ethanesulphonic acid) - MES (2[N-morpholino]ethane sulfonic acid) - TRICINE (N-tris[Hydroxymethyl]methyl glycine) - DMPA (N,N-dimethyl-1,3-propanediamine)     

Modulation of fatty acid-binding capacity of heart fatty acid-binding protein by oxygen — derived free radicals

Summary In this study, we examined the effects of exposure of heart fatty acid-binding protein (h-FABP) to chemically generated O₂ ^– or OH · with respect to its oleate binding and to its electrophoretic properties. Purified rat h-FABP at 40 M scavenged as much as 30% O₂ ^– and 85% OH ·. On the other hand, when 2 nmol (4 M) FABP were exposed to free radicals, the maximum oleate binding capacity as measured by Scatchard analysis was reduced only by 14% and 27% for O₂ ^– and OH ·, respectively. The electrophoretic pattern of free radical-exposed FABP was not markedly different when examined either by the non-denaturing or by denaturing PAGE, suggesting the absence of any degradation or aggregation of FABP by O₂ ^– or OH ·. It is hypothesized that O₂ ^– or OH · in physiological concentration may not alter the function of FABP markedly in the ischemic-reperfused myocardium.Abbreviations h-FABP Heart Fatty Acid Binding Protein - NEFA Non-Esterified Fatty Acids - O₂ ^– Superoxide anions - OH· hydroxyl radicals - OCI hypohalite radicals - H₂O₂ hydrogen peroxide - HPLC High Pressure Liquid Chromatography     

Cell membrane water permeability of rabbit cortical collecting duct

Summary The water permeability (P _osm) of the cell membranes of isolated perfused rabbit cortical collecting ducts was measured by quantitative light microscopy. Water permeability of the basolateral membrane, corrected for surface area, was 66 m·sec^–1 for principal cells and 62.3 m·sec^–1 for intercalated cells. Apical membraneP _osm values corrected for surface area, were 19.2 and 25 m·sec^–1 for principal and intercalated cells, respectively, in the absence of antidiuretic hormone (ADH). Principal and intercalated cells both responded to ADH by increasingP _osm of their apical membranes to 92.2 and 86.2 ·sec^–1 respectively. The ratio of the total basolateral cell membrane osmotic water permeability to that of the apical cell membrane was 271 in the absence of ADH and 71 in the presence of the hormone for both cell types. This asymmetry in water permeability is most likely due to the fact that basolateral membrane surface area is at least 7 to 8 times greater than that of the apical membrane. Both cell types exhibited volume regulatory decrease when exposed to dilute serosal bathing solutions. Upon exposure to a hyperosmotic serosal bath (390 mosm), pricipal cells did not volume regulate while two physiologically distinct groups of intercalated cells were observed. One group of intercalated cells failed to volume regulate; the second group showed almost complete volume regulatory increase behavior.     

Time course of vasopressin-induced formation of microvilli in granular cells of toad urinary bladder

Summary Vasopressin-induced transformation of ridges to microvilli on the surface of granular cells of toad urinary bladder occurs in conjunction with induced alterations in the water permeability of the luminal membrane. This study was designed to establish the relationship between the time course for induction of microvilli and the time course for induction of increased water permeability after vasopressin stimulation. Hemibladders were examined at 2.5, 5, 10, 20 and 30 min following exposure to 20 mU/ml of vasopressin and at 5, 10, 20, 30, 40, 50 and 60 min after washout of vasopressin. Within 2.5 min, vasopressin initiated complete transformation of ridges to microvilli on approximately 13% of the granular cells, while osmotic water flow (Jv) was 0.31±0.10 l·min^–1·cm^–2. Five minutes following vasopressin stimulation, microvilli were present on approximately 30% of granular cells andJv was 2.27±0.13 l·min^–1·cm^–2. At 10 minJv was maximum at 4.03±0.15 l·min^–1·cm^–2 and 50% of the granular cells were covered with microvilli. This percentage increased to 70% at 20 min and was maintained at 30 min, althoughJv decreased to 3.9±0.35 l·min^–1·cm^–2 at 30 min. Five minutes following vasopressin washout, ridges interspersed with microvilli reappeared asJv fell to 1.10±0.30 l·min^–1·cm^–2. At 10 min after vasopressin washout,Jv approached basal levels, but the reversal of microvilli to ridges remained incomplete. At 60 min after vasopressin washout, the granular cells had regained their original ridgelike surface structures. Thus, these studies establish a temporal relationship between the induction and reversibility of vasopressin-induced microvillous formation and alterations in the osmotic water permeability of the apical plasmalemma.     

n-3 PUFA productivity in chemostat cultures of microalgae

Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid productivities from chemostat cultures of an isolate of Isochrysis galbana have been studied. The productivities reached in the interval of dilution rates between 0.0295 h^–1 and 0.0355 h^–1 were 1.5mg·1^–1·h^–1 for lipids, 300 g·1^–1·h^–1 for EPA and 130g1·1^–1·h^–1 for DHA. Furthermore, light attenuation by mutual shading, and agitation speed influences on growth and fatty acid composition were analysed. A model relating steady-state dilution rates to internal average light intensity has been proposed, the parameter values of which obtained by non-linear regression were: maximum specific growth rate (_max)=0.0426 h^–1; the affinity of cells to light (I_k) = 10.92 W·m^–2; the exponent (n) = 5.13; regression coefficient (r ²)=0.9999. Correspondence to: E. Molina Grima     

Function and regulation of the avian caecal bulb: influence of dietary NaCl and aldosterone on water and electrolyte fluxes in the hen (Gallus domesticus) perfused in vivo

Summary The function of the caecal bulb, and its adaptation to chronic high- or low-Na⁺ intake, was investigated by in vivo perfusion of anaesthetised birds. Effects of acute aldosterone injection (125 g·kg^–1 body mass) were also measured.Evidence was found for primary active net absorption of Na⁺, inducing parallel Na-linked absorption of water and Cl^– and secretion of K⁺. Around 20–35% of total Cl^– absorption and K⁺ secretion were independent of Na⁺ fluxes, and these components appear to be driven by passive processes with apparent conductances of 6.3×10^–3 (G _Cl) and 1.1×10^–3 (G _K) S·cm^–2.Acetate (40mM) stimulated Na⁺ fluxes (8.5–9.9 Eq·cm^–2·h^–1) and Na-linked water fluxes (27–44 l·cm^–2·h^–1). Increased coupling ratios (2.9–4.6 l·Eq^–1) and other data indicate that these effects may be due to increased osmotic permeabilities of barriers involved in the Na-linked water transfer pathway.Low-Na⁺ maintenance enhanced EPD (49–69 mV, serosa positive) and all net fluxes:J _Na (6.8–11.6);J _K (–3.2––4.3);J _Cl (4.3–5.6 Eq·cm serosal area^–2·h^–1);J _v (28–43 l·cm^–2·h^–1) (mucosal-serosal fluxes positive).Acute aldosterone enhancedJ _Na (10.8–14.0 Eq·cm^–2·h^–1) and EPD (54–66 mV) by 3 h after injection, but had no effect on the Na-linked components ofJ _K orJ _Cl.Abbreviations ECPD, EPD Electrochemical or electrical potential difference - G _Cl ,G _K ionic conductances (Cl^–, K⁺) - J _v ,J _ion net volume or ion flux rate, mucosa-serosa positive;P _d (Cl) diffusive permeability coefficient (of Cl^–) - SEDM standard error of difference between means     

Organic reduction of tapioca wastewaters using modified RBC

A modified Rotating Biological Contactor (RBC) was used for the treatability studies of synthetic tapioca wastewaters. The RBC used was a four stage laboratory model and the discs were modified by attaching porous nechlon sheets to enhance biofilm area. Synthetic tapioca wastewaters were prepared with influent concentrations from 927 to 3600 mg/l of COD. Three hydraulic loads were used in the range of 0.03 to 0.09 m³·m^–2·d^–1 and the organic loads used were in the range of 28 to 306 g COD· m^–2·d^–1. The percentage COD removal were in the range from 97.4 to 68. RBC was operated at a rotating speed of 18 rpm which was found to be the optimal rotating speed. Biokinetic coefficients based on Kornegay and Hudson models were obtained using linear analysis. Also, a mathematical model was proposed using regression analysis.List of Symbols A m² total surface area of discs - d m active depth of microbial film onany rotating disc - K _s mg ·l^–1 saturation constant - P mg·m^–2·^–1 area capacity - Q l·d^–1 hydraulic flow rate - q m³·m^–2·d^–1 hydraulic loading rate - S ₀ mg·l^–1 influent substrate concentration - S _e mg·l^–1 effluent substrate concentration - w rpm rotational speed - V m³ volume of the reactor - X _f mg·l^–1 active biomass per unit volume ofattached growth - X _s mg·l^–1 active biomass per unit volume ofsuspended growth - X mg·l^–1 active biomass per unit volume - Y _s yield coefficient for attachedgrowth - Y _A yield coefficient for suspendedgrowth - Y yield coefficient, mass of biomass/mass of substrate removed Greek Symbols hr mean hydraulic detention time - (_max)_A d^–1 maximum specific growth rate forattached growth - (_max)_s d^–1 maximum specific growth rate forsuspended growth - _max d^–1 maximum specific growth rate - d^–1 specific growth rate - _v mg·l^–1·hr^–1 maximum volumetric substrateutilization rate coefficient     

Nitrate induction in spruce: an approach using compartmental analysis

Using ¹³NO ₃ ^– -efflux analysis, the induction of nitrate uptake by externally supplied nitrate was monitored in roots of intact Picea glauca (Moench) Voss. seedlings over a 5-d period. In agreement with our earlier studies, efflux analysis revealed three compartments, which have been identified as surface adsorption, apparent free space, and cytoplasm. While induction of nitrate uptake was pronounced, NO ₃ ^– fluxes in induced plants were decidedly lower and the induction response was slower than in other species. Influx rose from 0.1 mol·g^–1·h^–1 (measured at 100 M [NO ₃ ^– _o) in uninduced plants to a maximum of 0.5 mol·g^–1h^–1 after 3 d of exposure to 100 M [NO ₃ ^– _o and declined to 0.3–0.4 mol·g^–1h^–1 at the end of the 5-d period. Efflux remained relatively constant around 0.02-0.04 mol·g^–1h^–1, but its percentage with respect to influx declined from initially high values (around 30%) to steady-state values of 4–7%. Cytoplasmic [NO ₃ ^– ] ranged from the low micromolar in uninduced plants to a maximum of 2 mM in plants fully induced at 100 M [NO ₃ ^– ]_o. In-vivo root nitrate reductase activity (NRA) was measured over the same time period, and was found to follow a similar pattern of induction as influx. The maximum response in NRA slightly preceded that of influx. It increased from 25 nmol·g^–1·h^–1 without prior exposure to NO ₃ ^– to peak values around 150 nmol· g^–1h^–1 after 2 d of exposure to 100 M [NO ₃ ^– ]_o. Subsequently, NRA declined by about 50%. The dynamics of flux partitioning to reduction, to the vacuole, the xylem, and to efflux during the induction process are discussed.The research was supported by an Natural Sciences and Engineering Research Council, Canada, grant to Dr. A.D.M. Glass and by a University of British Columbia Graduate Fellowship to Herbert J. Kronzucker. Our thanks go to Dr. M. Adam and Mr. P. Culbert at the particle accelerator facility TRIUMF on the University of British Columbia campus for providing ¹³N, to Drs. R.D. Guy and S. Silim for providing plant material, and to Dr. M.Y. Wang, Mr. J. Bailey, Mr. J. Mehroke and Mr. J. Vidmar for essential assistance in experiments.     

Stem photosynthesis in Psorothamnus spinosus (smoke tree) in the Sonoran desert of California

Summary Stem photosynthetic responses to environmental parameters were investigated with Psorothamnus spinosus in the Sonoran Desert of California. Light saturation of stem photosynthesis was equal to maximum midday summer irradance (1600–2000 mol·m^-2·s^-1). The optimum temperature for stem photosynthesis was 39°C, and lower stem temperatures (27–35°C) caused significant decreases (up to 50%) in stem photosynthesis. Positive stem photosynthesis was maintained up to 51°C. Stem photosynthesis was relatively insensitive to increasing vpd up to 5 kPa; However, stem conductance decreased by 25% at a vpd of 5 kPa. At vpd greater than 5 kPa stem photosynthesis decreased relatively more than that of stem conductance causing a decrease in water use efficiency and an increase an intercellular carbon dioxide concentration. Maximum stem photosynthetic rates were low (6.2–10.6 mol·m^-2·s^-1) on a stem surface area, but, stem photosynthetic rates of young shoots were substantially higher (19.5–33.3 mol· m^-2·s^-1) on a projected area basis.Dedicated to the memory of Dr. W.H. Muller     

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     

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.     

CO2 gas exchange of the understory plantAsarum europaeum L. in November

The CO₂ gas exchange rates of the Central European perennial understory plantAsarum europaeum L. were measured in late autumn (October 30 to November 30) in its natural habitat day and night.During these measurements the temperature ranged from 0 to 15°C and the absolute air humidity from 3 to 10 mg H₂O·1^–1. Temperature and absolute air humidity over these ranges did not affect CO₂ net assimilation which was determined almost entirely by quantum flux density.CO₂ net assimilation was light saturated at about 100 M·m^–2·s^–1 quantum flux density. The uptake rate at this point was 4.3 mg·dm^–2·h^–1. The compensation point occurred at approximately 1 M·m^–2·s^–1.     

Surface charge and calcium binding in sarcoplasmic reticulum membranes

Vesicles of fragmented sarcoplasmic reticulum membranes have been adsorbed on to 2.68 latex spheres. Observation of these vesicle containing spheres in the presence of an electric field allows a calculation of the electrophoretic mobility of the vesicles Following this determination, the net membrane surface charge has been estimated. The mobility of sarcoplasmic reticulum membranes exhibited a dependency on pH. At an ionic strength of 0.10 a mobility (pH=7.0) of –0.67±0.10/sec/volt/cm was observed. At pH=7.0 and /2=0.150 the net excess negative charge density was 2.0×10^–2 coul/m². This is equivalent to one charge per 10³ A² (assuming a uniform charge distribution). With an average vesicle volume of 2.8×10⁸ A³ and a surface area of 2×10⁶ A² the surface of one vesicle would contain a net of approximately 2×10³ negative charges. While the mobility did not change during uptake of calcium by the vesicles, both glutaraldehyde fixation and lecithin extraction by phospholipase C greatly altered the mobility of the vesicle membrane. Calcium binding and uptake both exhibited a dependence on pH.     

Continuous monitoring of cellulase action on microcrystalline cellulose

Summary Cellobiose oxidase from Phanerochaete chrysosporium was used for continuous monitoring of cellulase action on microcrystalline cellulose (Avicel). Two protocols are described, the parameter monitored being either the decline in electrode potential as ferricyanide is reduced or consumption of dioxygen. Most experiments used a commercial cellulase preparation from Trichoderma reesei and ferricyanide as acceptor. Within 1 min of an addition of cellulase, ferricyanide reduction reached a steady rate. This was converted into a rate of production of substrate for celobiose oxidase, in mol·min^–1. Experiments were conducted either with a constant concentration of cellulase and increasing Avicel, or with constant Avicel and increasing cellulase. Kinetic analysis of the experiments with constant cellulase indicated a K _mof 4.8 ± 1.0 (g cellulose)·1^–1, which was close to the value predicted from binding studies. The specific activity of the cellulase was measured as 375±25 mol·(g cellulase)^–1·min^–1 in experiments with a high cellulose concentration, but was less than half this value when the cellulose was saturated with cellulase. The maximal rate of cellulose degradation was 9.6±1.3 mol·(g cellulose)^–1·min^–1.     

Bacterial productivity and microbial biomass in tropical mangrove sediments

Bacterial productivity (³H-thymidine incorporation into DNA) and intertidal microbenthic communities were examined within five mangrove estuaries along the tropical northeastern coast of Australia. Bacteria in mangrove surface sediments (0–2 cm depth) were enumerated by epifluorescence microscopy and were more abundant (mean and range: 1.1(0.02–3.6)×10¹¹ cells·g DW^–1) and productive (mean: 1.6 gC·m^–2· d^–1) compared to bacterial populations in most other benthic environments. Specific growth rates (¯x=1.1) ranged from 0.2–5.5 d^–1, with highest rates of growth in austral spring and summer. Highest bacterial numbers occurred in winter (June–August) in estuaries along the Cape York peninsula north of Hinchinbrook Island and were significantly different among intertidal zones and estuaries. Protozoa (10⁵–10⁶·m^–2, pheopigments (0.0–24.1g·gDW^–1) and bacterial productivity (0.2–5.1 gC·m^–2·d^–1) exhibited significant seasonality with maximum densities and production in austral spring and summer. Algal biomass (chlorophylla) was low (mean: 1.6g·gDW^–1) compared to other intertidal sediments because of low light intensity under the dense forest canopy, especially in the mid-intertidal zone. Partial correlation analysis and a study of possible tidal effects suggest that microbial biomass and bacterial growth in tropical intertidal sediments are regulated primarily by physicochemical factors and by tidal flushing and exposure. High microbial biomass and very high rates of bacterial productivity coupled with low densities of meiofaunal and macroinfaunal consumers observed in earlier studies suggest that microbes may be a sink for carbon in intertidal sediments of tropical mangrove estuaries.     

Optimization of pyrite bioleaching using Sulfolobus acidocaldarius

Optimization of batch pyrite bioleaching with Sulfolobus acidocaldarius was performed using statistical modelling and experimental design. First a screening design was made followed by response surface modelling. The dominating factors identified were pH, pulp density and particle size. The highest batch leaching rate after optimization was 270 mg iron·l^–1·h^–1 for 6% (w/v) pulp density, pH = 1.5 and particle size <20 m. This represents a 3.5-fold increase from the leaching rate of 80 mg iron·l^–1·h^–1 obtained under our standard laboratory conditions. Correspondence to: E. B. Lindström     

Immobilization of epoxide hydrolase purified from rat liver microsomes

Summary Purified epoxide hydrolase was immobilized by covalent binding to Sephadex G-150 activated with 1,1 carbonyl diimidazole under mild conditions Km^app values of free and immobilized epoxide hydrolase were 0.5 M and 2 M respectively towards benzo(a)pyrene-4,5-oxide, whereas Vmax^app was decreased from 300 nmol·min^–1·mg^–1 to 81 nmol·min^–1·mg^–1. Immobilization enhanced stability and allowed repeated use of the enzyme.