Biophysical responses of red cell-membrane systems to very low concentrations of inorganic mercury

Changes in red blood cellsize, deformability, andosmotic fragility are indicators of altered condition and/or altered regulatory processes at the whole cell and membrane levels. An agent, such as HgCl₂, that brings about specific changes of this kind can therefore serve as a selective probe of such cell condition and regulatory state. Conversely, for a health-threatening agent “active” in this way, the cell-membrane responses serve to clarify the more fundamental bases of its toxicity, as well as to permit identification and characterization of its early and low-level actions on living systems. Taking advantage of recent advances in the technique of “resistive pulse spectroscopy,” we present a coordinated study of these three interrelated biophysical properties for the interactions of HgCl₂ with human red cells. We thereby are able to extend previous studies of this kind into domains of shorter time (instantaneous exposures), lower level exposures (down to 10⁻⁹ M, well below the level of acute human toxicity), as well as to additional kinds of responses (e.g., “dynamic osmotic hemolysis”). For conditions ranging from 10⁻⁴ to 10⁻⁹ M in HgCl₂, for instantaneous to 90-min-incubated exposures, for medium osmolarities from 120 to 300, the matrix of observed cell responses includes relative swelling as well as shrinkage, changes in deformability, and both enhancement of and protection against osmotic hemolysis. Some unexpected short-term effects of time and temperature of storage of blood cell stock samples, with respect to increasing and decreasing osmotic fragility, are also reported. These apparently disparate results are interpreted in terms of mercury interactions with cell and membrane SH groups, and a reasonable rationale is presented for most of the responses in terms of disruption of passive and active Na⁺−K⁺, gradient controls, plus interactions with cellular proteins.     

Impact of soil vertical water movement on the energy balance of different land surfaces

The soil heat flux determination method proposed by Gao (Boundary-Layer Meteorol 114:165–178, 2005) is discussed for (1) dry surfaces, (2) bare soil or sparse short-grass lands, and (3) dense-grass surfaces or forest. Our analysis shows that, when neglecting the contribution of soil vertical water movement to soil heat flux, the energy components measured independently will (1) still achieve balance over dry surfaces, and (2) be significantly in imbalance over bare soil or sparse short-grass lands. The mean of bare ground evaporation modeled by SiB2 is 1.58 × 10⁻⁵ m³ s⁻¹ m⁻², and the mean of soil water flux obtained by the method of Gao is 1.22 × 10⁻⁵ m³ s⁻¹ m⁻² for the Naqu site in the summer of 1998. Comparison of the bare ground evaporation with the mean of soil water flux shows a difference, the causes of which are investigated. Physically, the bare ground evaporation is equal to the sum of soil water flux and water content change in the soil surface layer. Because the bare ground evaporation is very limited for the dense-grass surfaces or forest, our analysis implies that the energy imbalance encountered over the dense-grass or forest is not caused by the fact that previous researchers neglected soil water movements in their energy budget analyses.     

Effects of Lens Major Intrinsic Protein on Glycerol Permeability and Metabolism

Lens Major Intrinsic Protein (MIP) is a member of a family of membrane transport proteins including the Aquaporins and bacterial glycerol transporters. When expressed in Xenopus oocytes, MIP increased both glycerol permeability and the activity of glycerol kinase. Glycerol permeability (p _Gly ) was 2.3 ± 0.23 × 10⁻⁶ cm sec⁻¹ with MIP vs. 0.92 ± 0.086 × 10⁻⁶ cm sec⁻¹ in control oocytes. The p _Gly of MIP was independent of concentration from 5 × 10⁻⁵ to 5 × 10⁻² m, had a low temperature dependence, and was inhibited approximately 90%, 80% and 50% by 1.0 mm Hg⁺⁺, 0.2 mm DIDS (diisothiocyanodisulfonic stilbene), and 0.1 mm Cu⁺⁺, respectively. MIP-enhanced glycerol phosphorylation, resulting in increased incorporation of glycerol into lipids. This could arise from an increase in the total activity of glycerol kinase, or from an increase in its affinity for glycerol. Based on methods we present to distinguish these mechanisms, MIP increased the maximum rate of phosphorylation by glycerol kinase (0.12 ± 0.03 vs. 0.06 ± 0.01 pmol min⁻¹ cell⁻¹) without changing the binding of glycerol to the kinase (K _M ∼ 10 μm). Received: 23 May 1997/Revised: 4 August 1997     

Biodegradation of an aldehyde biocide in rotating biological contactors

Biodegradation of an aldehyde biocide, glutaraldehyde (GA), in a single-stage laboratory-scale rotating biological contactor (RBC) was studied under biocide or organic loadings (OL) of 12–66 g COD m⁻² day⁻¹ and hydraulic retention times (HRT) of 0.6–3.0 h. Biofilms on the RBC were acclimated in 180 ppm GA at a hydraulic loading (HL) of 0.18 m³ m⁻² day⁻¹ and the HRT of 0.60 h. The results showed that under a constant initial chemical oxygen demand (COD) concentration and sufficient mineral salts available, the degree of GA removal in the RBC system was increased with either decreasing OL or increasing HRT. After a period of acclimation, treatment efficiency in terms of GA removal by the RBC receiving GA as a sole carbon source was 89%. The biofilms played an important role in biodegradation of biocide in the RBCs, whereas bio-oxidation of their planktonic counterparts was totally inhibited in the presence of 50 ppm GA. The biochemical oxygen demand (BOD) test could be used as an appropriate analytical procedure for investigating the efficiency of wastewater treatment units when seed was acclimated and had adequate amount.     

In Vitro Culture of Rudimentary Embryos of Ilex paraguariensis: Responses to Exogenous Cytokinins

The effects of benzyladenine (BAP), kinetin (KIN), zeatin (ZEA), isopentenyladenine (2iP), and thidiazuron (TDZ) were studied on in vitro growth of rudimentary embryos of Ilex paraguariensis St. Hil. Heart stage zygotic embryos were removed from seeds of immature, light green fruits and cultured aseptically on quarter-strength Murashige and Skoog medium containing 3% sucrose, 0.65% agar, and supplemented with or without three concentrations of BAP, KIN, ZEA, 2iP, or TDZ. Cultures were incubated in darkness at 27 ± 2°C. Media containing 4.4 × 10⁻⁶ m BAP, 4.6 × 10⁻⁶ m KIN, or 4.9 × 10⁻⁶ m 2iP were totally ineffective in inducing embryo growth after culture for 28 days. However, lower concentrations of these compounds (4.4 × 10⁻⁸ m BAP, 4.6 × 10⁻⁸ m KIN, 4.5 × 10⁻⁸ m ZEA, or 4.9 × 10⁻⁸ m 2iP) promoted embryo growth. TDZ at 9.9 × 10⁻⁹ m, 9.9 × 10⁻⁸ m, or 9.9 × 10⁻⁷ m induced embryo growth at similar rates. The maximum percentage of embryos converted to seedlings was achieved when the medium was supplemented with 4.5 × 10⁻⁷ m ZEA. Received August 1, 1997; accepted February 19, 1998     

Scaling food chains in aquatic mesocosms: do the effects of depth override the effects of planktivory?

To assess the effects of physical dimension and planktivorous fish on phytoplankton standing crop, we repeated an experiment at different scales in plastic enclosures during summer 1995 in Lake Créteil, France. Enclosures were scaled for a constant surface (1.5 × 1.5 m) as depth was increased from 2.5 to 4.5 m. Even-link (zooplankton and phytoplankton) and odd-link (planktivorous fish, zooplankton and phytoplankton) food webs were established in both shallow and deep enclosures. Fish densities in the deep enclosures were scaled to allow comparisons with shallow ones for both in individuals m⁻² or individuals m⁻³. We explicitly designed this experiment to examine the scale-dependent behavior of the top-down mechanism of algal biomass control in lakes, and in particular to test the hypothesis of stronger cascading effects of fish on lower trophic levels at reduced depth. Both fish and enclosure size had highly significant effects on phytoplankton biomass over the duration of the experiment. No depth × fish interaction effects were observed. The presence of planktivorous fish enhanced phytoplankton biomass in both shallow and deep enclosures, although the reduction in depth generally produced a stronger effect. The mean concentration of chlorophyll a in the deep odd-link systems (ca 5 mg m⁻³) was lower than in the shallow even-link systems (ca 17 mg m⁻³). Statistical interpretation did not change when data were expressed as phytoplankton biomass per unit of surface area. Light limitation and zooplankton grazing are the most probable mechanisms explaining our results in these nutrient-enriched systems. Moreover, we found that the strength of the cascading effect of fish on plankton was not a function of depth. We believe that further studies on scaling effects should be conducted in order to improve our understanding of ecological patterns and to extrapolate results from micro/mesocosms to natural ecosystems. Received: 18 January 1999 / Accepted: 7 June 1999     

Even patients with mild COVID‐19 symptoms after SARS‐CoV‐2 infection show prolonged altered red blood cell morphology and rheological parameters

Infection with the novel severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2) and the associated coronavirus disease‐19 (COVID‐19) might affect red blood cells (RBC); possibly altering oxygen supply. However, investigations of cell morphology and RBC rheological parameters during a mild disease course are lacking and thus, the aim of the study. Fifty individuals with mild COVID‐19 disease process were tested after the acute phase of SARS‐CoV‐2 infection (37males/13 females), and the data were compared to n = 42 healthy controls (30 males/12 females). Analysis of venous blood samples, taken at rest, revealed a higher percentage of permanently elongated RBC and membrane extensions in COVID‐19 patients. Haematological parameters and haemoglobin concentration, MCH and MCV in particular, were highly altered in COVID‐19. RBC deformability and deformability under an osmotic gradient were significantly reduced in COVID‐19 patients. Higher RBC‐NOS activation was not capable to at least in part counteract these reductions. Impaired RBC deformability might also be related to morphological changes and/or increased oxidative state. RBC aggregation index remained unaffected. However, higher shear rates were necessary to balance the aggregation‐disaggregation in COVID‐19 patients which might be, among others, related to morphological changes. The data suggest prolonged modifications of the RBC system even during a mild COVID‐19 disease course.     

Inhibitory effect of ethylenediaminetetraacetate (EDTA) on the porcine lymphocyte response to mitogens and reversal of the effect with metal ions

The effect of ethylenediaminetetraacetate (EDTA) on the mitogen response of porcine lymphocytes and the role of metal ions in reversal of the inhibitory effect of EDTA were determined. Porcine lymphocyte responses to mitogens were totally suppressed when serum used to supplement Ca²⁺, Mg²⁺-free minimum essential medium (MEM) was dialyzed against saline or saline with 0.2 or 0.60 mM EDTA, but the responses were only partially reduced when the same serum was added to RPMI-1640 medium. The inhibition observed in MEM could be reversed by adding 1×10⁻³ M Ca²⁺ and 1×10⁻³ M Mg²⁺ to the dialyzed serum. Serum treated directly with 0.60 mM EDTA completely suppressed blastogenesis in lymphocyte cultures maintained in RPMI-1640 or Ca²⁺, Mg²⁺ free MEM. The inhibitory effect of EDTA-treated serum could be completely reversed by adding Zn²⁺ or a combination of Zn²⁺ with other cationic ions, or partially reversed by adding Ni²⁺ or Fe³⁺. Zn²⁺ was the most effective ion, in that it was the only ion that, when alone added to the serum, could completely restore lymphocyte responses to phytohemagglutinin (PHA) or pokeweed mitogen (PWM).     

Effects of monovalent cations on red cell shape and size

Human erythrocytes were incubated in isotonic solutions of different monovalent cations. The apparent size of the red cells measured on scanning electron microscopic pictures decreases in the order Li⁺>Na⁺=K⁺>Rb⁺. These differences in size are abolished after pretreatment with trypsin, which removes a large part of the charges associated with membrane glycoproteins. Shape alterations are also observed. Normal biconcave shapes are visible after Na⁺ or K⁺ incubation, whereas Li⁺ leads to flabby, flattened cells with a certain tendency to crenation, and Rb⁺ causes more pronounced biconcavity with a certain tendency to cupping. The overall effects of pretreatment with trypsin are similar to those of Li⁺. Our results provide evidence that the electrostatic repulsion of glycoproteins and other charged membrane components may play an essential role in maintaining red cell shape.     

Determination of the kinetics of permeation of dimethyl sulfoxide in isolated corneas

Corneal cryopreservation requires that endothelial cells remain viable and intercellular structure be preserved. High viability levels for cryopreserved endothelial cells have been achieved, but preserving intercellular structure, especially endothelial attachment to Descemet's membrane, has proved difficult. Cell detachment apparently is not caused by ice, suggesting osmotic or chemical mechanisms. Knowledge of the permeation kinetics of cryoprotectants (CPAs) into endothelial cells and stroma is essential for controlling osmotic and chemical activity and achieving adequate tissue permeation prior to cooling. Proton nuclear magnetic resonance (NMR) spectroscopy was used to assess the permeation of dimethyl sulfoxide (DMSO) into isolated rabbit corneas. Corneas with intact epithelia were exposed to isotonic medium or 2.0 mol/L DMSO for 60 min and subsequently transferred to 2.0 or 4.0 mol/L DMSO, respectively, at 22, 0, or −10°C. DMSO concentration in the cornea was measured vs time. The Kedem-Katchalsky model was fitted to the data. Hydraulic permeability (m³/N·s) is 7.1×10⁻¹³+216%-11% at 22°C, 8.2×10⁻¹³+235%−21% at 0°C, and 1.7×10⁻¹⁴+19% −16% at −10°C. The reflection coefficient is 1.0+2%−1% at 22°C and 0°C, and 0.9±5% at −10°C. Solute mobility (cm/s) is 5.9×10⁻⁶+6%–11% at 22°C, 3.1×10⁻⁶+12%−11% at 0°C, and 5.0×10⁻⁸ cm/s+59%−40% at −10°C.     

Toxicity assessment of paraverine hydrochloride and papaverine-derived metabolites in primary cultures of rat hepatocytes

Summary The present study was undertaken to assess and compare the toxic effects of papaverine hydrochloride and its metabolites. Primary cell cultures of rat hepatocytes were treated with papavarine (papaver), 3′-O-desmethyl (3′-OH), 4′-O-desmethyl (4′-OH), and 6-O-desmethyl (6-OH) papaverine at 1×10⁻⁵, 1×10⁻⁴, and 1×10⁻³ M for 4,8, 12, and 24-h periods. Cell injury was determined by: a) cell viability using the trypan blue exclusion test; b) cytosolic enzyme leakage of lactate dehydrogenase and aspartate aminotransferase; c) morphologic alterations; and d) lactate: pyruvate (L:P) ratios. Cell cultures showed concentration-and time-dependent responses. For example, a decrease in cell viability and an increase in enzyme leakage were observed after cell treatment with 1×10⁻⁴ and 1×10⁻³ M papaver for 8 h; 1×10⁻³ M 6-OH papaverine for 8 h and 1×10⁻⁴ M for 24 h; and 1×10⁻³ M 4′-OH papaverine for 24 h (P<0.05). Furthermore, changes in morphology correlated to cell viability and enzyme release in those cultures treated with papaver, 4′-OH and 6-OH papaverine. Some of these changes included size deformation, cell detachment from the dishes, and cell necrosis. On the other hand, an increase in L:P ratios (P<0.05) was detected with papaver as early as 8 h with 1×10⁻⁴ and 1×10⁻³ M and 12 h with 1×10⁻⁵ M; 6-OH showed an increase, in L:P ratios at 8 h with 1×10⁻³ M and 12 h with 1×10⁻⁴ M; these changes were evident with 4′-OH at 12 h with 1×10⁻³ M. In contrast, cells treated with 3′-OH papaverine did not show significant damage with any time period and concentration used in this study. The results of this study indicate that papaverine-derived metabolites are less cytotoxic than its parent compound, papaver. The toxicity was ranked as follows: papaver>6-OH>4′-OH>−3′-OH. This work was supported in part by grant ES04200-02 from the National Institute of Environmental Health Sciences, Bethesda, MD. Presented in part at the fall ASPET meeting in Salt Lake City, August, 1989. Daniel Acosta is a Burroughs Wellcome Scholar in Toxicology.     

H+ ATPase and Cl− Interaction in Regulation of MDCK Cell pH

MDCK cells display several acid-base transport systems found in intercalated cells, such as Na⁺-H⁺ exchange, H⁺–K⁺ ATPase and Cl⁻/HCO⁻ ₃ exchange. In this work we studied the functional activity of a vacuolar H⁺-ATPase in MDCK cells and its chloride dependence. We measured intracellular pH (pHi) in monolayers grown on glass cover slips utilizing the pH sensitive probe BCECF. To analyze the functional activity of the H⁺ transporters we observed the intracellular alkalinization in response to an acute acid load due to a 20 mm NH⁺ ₄ pulse, and calculated the initial rate of pHi recovery (dpHi/dt). The cells have a basal pHi of 7.17 ± 0.01 (n= 23) and control dpHi/dt of 0.121 ± 0.006 (n= 23) pHi units/min. This pHi recovery rate is markedly decreased when Na⁺ was removed, to 0.069 ± 0.004 (n= 16). It was further reduced to 0.042 ± 0.005 (n= 12) when concanamycin 4.6 × 10⁻⁸ m (a specific inhibitor of the vacuolar H⁺-ATPase) was added to the zero Na⁺ solution. When using a solution with zero Na⁺, low K⁺ (0.5 mm) plus concanamycin, pHi recovery fell again, significantly, to 0.023 ± 0.006 (n= 14) as expected in the presence of a H⁺–K⁺-ATPase. This result was confirmed by the use of 5 × 10⁻⁵ m Schering 28080. The Na⁺ independent pHi recovery was significantly reduced from 0.069 ± 0.004 to 0.042 ± 0.004 (n= 12) when NPPB 10⁻⁵ m (a specific blocker of Cl⁻ channels in renal tubules) was utilized. When the cells were preincubated in 0 Cl⁻/normal Na⁺ solution for 8 min. before the ammonium pulse, the pHi recovery fell from 0.069 ± 0.004 to 0.041 ± 0.007 (n= 12) in a Na⁺ and Cl⁻ free solution. From these results we conclude that: (i) MDCK cells have two Na⁺-independent mechanisms of pHi recovery, a concanamycin sensitive H⁺-ATPase and a K⁺ dependent, Schering 28080 sensitive H⁺–K⁺ ATPase; and, (ii) pHi recovery in Na⁺-free medium depends on the presence of a chloride current which can be blocked by NPPB and impaired by preincubation in Cl⁻–free medium. This finding supports a role for chloride in the function of the H⁺ ATPase, which might be electrical shunting or a biochemical interaction. Received: 24 October 1997/Revised: 19 February 1998     

Decrease of phosphoribulokinase activity by antisense RNA in transgenic tobacco: definition of the light environment under which phosphoribulokinase is not in large excess

 To test the hypothesis that the contribution of phosphoribulokinase (PRK) to the control of photosynthesis changes depending on the light environment of the plant, the response of transgenic tobacco (Nicotiana tabacum L.) transformed with antisense PRK constructs to irradiance was determined. In plants grown under low irradiance (330 μmol m⁻² s⁻¹) steady-state photosynthesis was limited in plants with decreased PRK activity upon exposure to higher irradiance, with a control coefficient of PRK for CO₂ assimilation of 0.25 at and above 800 μmol m⁻² s⁻¹. The flux control coefficient of PRK for steady-state CO₂ assimilation was zero, however, at all irradiances in plant material grown at 800 μmol m⁻² s⁻¹ and in plants grown in a glasshouse during mid-summer (alternating shade and sun 300–1600 μmol m⁻² s⁻¹). To explain these differences between plants grown under low and high irradiances, Calvin cycle enzyme activities and metabolite content were determined. Activities of PRK and other non-equilibrium Calvin cycle enzymes fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase and ribulose-1,5-bisphosphate carboxylase-oxygenase were twofold higher in plants grown at 800 μmol m⁻² s⁻¹ or in the glasshouse than in plants grown at 330 μmol m⁻² s⁻¹. Activities of equilibrium enzymes transketolase, aldolase, ribulose-5-phosphate epimerase and isomerase were very similar under all growth irradiances. The flux control coefficient of 0.25 in plants grown at 330 μmol m⁻² s⁻¹ can be explained because low ribulose-5-phosphate content in combination with low PRK activity limits the synthesis of ribulose-1,5-bisphosphate. This limitation is overcome in high-light-grown plants because of the large relative increase in activities of sedoheptulose-1,7-bisphosphatase and fructose-1,6-bisphosphatase under these conditions, which facilitates the synthesis of larger amounts of ribulose-5-phosphate. This potential limitation will have maintained evolutionary selection pressure for high concentrations of PRK within the chloroplast. Received: 15 November 1999 / Accepted: 27 January 2000     

Bacterioplankton of the Gdansk Basin,Baltic Sea

The numbers, biomass, and production of bacterioplankton were determined in the Russian Sector of the Gdansk Basin (Baltic Sea) in 2007–2009. Significant spatial and temporal variations were determined. During the year, bacterial activity increased with increasing water temperature and higher availability of organic substrates. The lowest bacterial production (0.01–31.63 mg C m⁻³ day⁻¹) was observed in late winter and late autumn, while the highest (0.17–341.70 mg C m⁻³ day⁻¹) occurred in spring and summer. Since bacterial numbers and biomass were found to depend on the weather conditions and the terrigenous inflow, significant variations were observed from year to year. The highest and lowest numbers and biomass of bacterioplankton determined in summer were 0.09–1.10 × 10⁶ cells mL⁻¹ and 2–22 mg C m⁻³ for July 2007 and 1.96–11.23 × 10⁶ cells mL⁻¹ and 23–123 mg C m^–3 for July 2009. The values of these parameters were the highest along the coast and decreased towards the open sea.     

Red blood cell dielectrophoresis in axisymmetric fields

Dielectrophoretic velocities of human red blood cells in an axisymmetric field were measured as a function of the applied voltage and the distance from the axis of symmetry. The voltage of the alternating electric field (frequency 2 MHz), applied between two concentric cylindrical metal electrodes (outer and inner radii 0.24 and 1 mm, respectively), was varied up to 19 V. Two kinds of mediums were used: (a) 90% of 2.1% glycine solution and 10% of 5.5% glucose solution and (b) 5.4% sorbitol solution. The results have shown that in both mediums the cell velocities are proportional to the square of the applied voltage and inversely proportional to the cube of the distance from the axis of symmetry, as predicted by the theory. The coefficient of proportionality (dielectrophoretic coefficient) is on the order of 10⁻²⁵ A²s⁴kg⁻¹. It depends on the donor of red blood cells and might be used for diagnostic purposes. These results will be used in future investigations of membrane adhesion, stability and fusion.     

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.     

Diamine oxidase from millet catalyzes the oxidation of 1, 3-diaminopropane

Diamine oxidase was purified sixty-fold from millet shoots. The partially purified enzyme of 150 kDa oxidized 1, 3-diaminopropane (1, 3-DAP) to 3-aminopropionaldehyde. The K_m values were 9.1×10⁻⁵M for 1, 3-DAP and 6.3×10⁻⁴M for putrescine. Extracts of shoots of prosomillet, maize and barley also contained an activity that oxidized 1, 3-DAP.     

Comparison of relative rates of BTEX biodegradation using respirometry

Biodegradation of BTEX by a microbial consortium isolated from a closed municipal landfill was studied using respirometric techniques. The kinetics of biodegradation were estimated from experimental oxygen uptake data using a nonlinear parameter estimation technique. All of the six compounds were rapidly degraded by the microbial culture and no substrate inhibition was observed at the concentration levels examined (200 mg L⁻¹ as COD). Microbial growth and contaminant degradation were adequately described by the Monod equation. Considerable differences were observed in the rates of BTEX biodegradation as seen from the estimates of the kinetic parameters. A three-fold variation was seen in the values of the maximum specific growth rate, μ_max. The highest value of μ_max was 0.389 h⁻¹ for p-xylene while o-xylene was characterized by a μ_max value of 0.14 h⁻¹, the lowest observed in this study. The half saturation coefficient, K _s, and the yield coefficient, Y, varied between 1.288–4.681 mg L⁻¹ and 0.272–0.645 mg mg⁻¹, respectively. Benzene and o-xylene exhibited higher resistance to biodegradation while toluene and p-xylene were rapidly degraded. Ethylbenzene and m-xylene were degraded at intermediate rates. In biodegradation experiments with a multiple substrate matrix, substrate depletion was slower than in single substrate experiments, suggesting an inhibitory nature of substrate interaction. Received 15 February 1998/ Accepted in revised form 5 July 1998     

Temperature and irradiance impacts on the growth,pigmentation and photosystem II quantum yields of <Emphasis Type="Italic">Haematococcus pluvialis</Emphasis> (Chlorophyceae)

The microalga Haematococcus pluvialis Flotow has been the subject of a number of studies concerned with maximizing astaxanthin production for use in animal feeds and for human consumption. Several of these studies have specifically attempted to ascertain the optimal temperature and irradiance combination for growth of H. pluvialis, but there has been a great deal of disagreement between laboratories. “Ideal” levels of temperature and irradiance have been reported to range from 14 to 28°C and 30 to 200 μmol photons m⁻² s⁻¹. The objective of the present study was to simultaneously explore temperature and irradiance effects for a single strain of H. pluvialis (UTEX 2505) across an experimental region that encompassed the reported “optimal” combinations of these factors for multiple strains. To this end, a two-dimensional experimental design based on response surface methodology (RSM) was created. Maximum growth rates for UTEX 2505 were achieved at 27°C and 260 μmol photons m⁻² s⁻¹, while maximum quantum yield for stable charge separation at PSII (F_v/F_m) was achieved at 27°C and 80 μmol photons m⁻² s⁻¹. Maximum pigment concentrations correlated closely with maximum F_v/F_m. Numeric optimization of growth rate and F_v/F_m produced an optimal combination of 27°C and 250 μmol photons m⁻² s⁻¹. Polynomial models of the various response surfaces were validated with multiple points and were found to be very useful for predicting several H. pluvialis UTEX 2505 responses across the entire two-dimensional experimental design space.     

Bacillus thuringiensis CrylAa δ-Endotoxin Affects the K+/Amino Acid Symport in Bombyx mori Larval Midgut

The mechanical properties of brush border membrane vesicles, BBMV, from rabbit kidney proximal tubule cells, were studied by measuring the initial and final equilibrium volumes of vesicles subjected to different osmotic shocks, using cellobiose as the impermeant solute in the preparation buffer. An elevated intracellular hydrostatic pressure was inferred from osmotic balance requirements in dilute solutions. For vesicles prepared in 18 and 85 mosm solutions, these pressures are close to 17 mosm (290 mm Hg). The corresponding membrane surface tension is 6.0 × 10⁻⁵ N cm⁻¹ while the membrane surface area is expanded by at least 2.2%. When these vesicles are exposed to very dilute solutions the internal hydrostatic pressure rises to an estimated 84 mosm (1444 mm Hg) just prior to lysis. The corresponding maximal surface tension (pre-lysis) is 18.7 × 10⁻⁵ N cm⁻¹, and the maximal expansion of membrane area is 6.8%. The calculated area compressibility elastic modulus was 2.8 × 10⁻³ N cm⁻¹. Received: 8 August 1996/Revised: 4 March 1997