The effects of hydration and divalent cations on lamellar-nonlamellar phase transitions in membranes and total lipid extracts from Acholeplasma laidlawii A-EF22 – a 2H NMR study

Acholeplasma laidlawii strain A-EF22 was grown in a medium supplemented with 75 μm α-deuterated palmitic acid (16:0-d ₂) and 75 μm α-deuterated oleic acid (18:1c-d ₂), or with 150 μm 18:1c-d ₂. The fatty acids were incorporated into the membrane lipids and ²H NMR spectra were recorded from intact membranes, total lipid extracts, and the combined glucolipid and neutral lipid fractions of a total lipid extract. The lipids in intact membranes form a bilayer structure up to at least 70 °C. The same result was obtained with membranes digested with pronase, which removes a large fraction of the membrane proteins. A reversed hexagonal liquid crystalline (H_II) phase was formed below 70 °C by the total lipid extracts hydrated with 20 and 30% (w/w) water; in the presence of 40% (w/w) water only one of the extracts formed an H_II phase below 70 °C. The H_II phase was formed at higher temperatures with an increasing water content. However, only a lamellar liquid crystalline (L _α ) phase was formed up to 70 °C by the total lipid extracts when the water concentrations were 50% (w/w) or higher. The temperature (T _LH) for the L _α to H_II phase transition in the combined glucolipid and neutral lipid fractions was only 2–3 °C lower than for the total lipids, and the phospholipids thus have a very modest influence on the T _LH value. Physiologically relevant concentrations of Ca²⁺ and Mg²⁺ ions did not affect the phase equilibria of total lipid extracts significantly. It is concluded from comparison with published data that the membrane lipids of the cell wall-less bacterium A. laidlawii have a smaller tendency to form reversed nonlamellar phases than the membrane lipids of three bacterial species surrounded by a cell wall. Received: 10 March 1997 / Accepted: 4 July 1997     

Isolation and characterization of mammalian D-aspartyl endopeptidase

Summary. The accumulation of D-isomers of aspartic acid (D-Asp) in proteins during aging has been implicated in the pathogenesis of Alzheimer’s disease (AD), cataracts and arteriosclerosis. Here, we identified a specific lactacystin-sensitive endopeptidase that cleaves the D-Asp-containing protein and named it D-aspartyl endopeptidase (DAEP). DAEP has a multi-complex structure (MW: 600 kDa) and is localized in the inner mitochondrial membrane. However, DAEP activity was not detected in E. coli, S. cerevisiae, and C. elegans. A specific inhibitor for DAEP, i-DAEP: (benzoyl-L-Arg-L-His-[D-Asp]-CH₂Cl; MW: 563.01), was newly synthesized and inhibited DAEP activity (IC₅₀, 3 μM), a factor of ten greater than lactacystin on DAEP. On the other hand, i-DAEP did not inhibit either the 20S or 26S proteasome. And we identified succinate dehydrogenase and glutamate dehydrogenase 1 as components of DAEP by affinity label using biotinylated i-DAEP. In the long life span of mammals, DAEP may serve as a scavenger against accumulation of racemized proteins in aging. Insights into DAEP will provide the foundation for developing treatments of diseases, such as AD, in which accumulation of D-Asp-containing proteins are implicated.     

Kinetic analysis of the active site of an intracellular β-glucosidase fromCellulomonas biazotea

Purified β-glucosidase fromCellulomonas biazotea had an apparentK _m andV for 2-nitrophenyl β-d-glucopyranoside (oNPG) of 0.416 mmol/L and 0.22 U/mg protein, respectively. The activation energy for the hydrolysis of pNPG of β-glucosidase was 65 kJ/mol. The inhibition by Mn²⁺ vs. oNPG of parental β-glucosidase was of mixed type with apparent inhibition constants of 0.19 and 0.60 μmol/L for the enzyme and enzyme-substrate complex, respectively. Ethanol at lower concentrations activated while at higher concentrations it inhibited the enzyme. The determination of apparent pK _a’s at different temperatures and in the presence of 30 % dioxane indicated two carboxyl groups which control theV value. The thermal stability of β-glucosidase decreased in the presence of 10 % ethanol. The half-life of β-glucosidase in 1.75 mol/L urea at 35 °C was 145 min, as determined by 0–9 mol/L transverse urea gradient-PAGE. This work was financed in part by a grant made by theUS Agency for International Development under PSTC proposal 6-163,USAID grant no. 9365542-G-00-89-42-00, and PAEC.     

Characterization of the catalytically active Mn(II)-loaded argE -encoded N -acetyl-l -ornithine deacetylase from Escherichia coli

The catalytically competent Mn(II)-loaded form of the argE-encoded N-acetyl-l-ornithine deacetylase from Escherichia coli (ArgE) was characterized by kinetic, thermodynamic, and spectroscopic methods. Maximum N-acetyl-l-ornithine (NAO) hydrolytic activity was observed in the presence of one Mn(II) ion with k _cat and K _m values of 550 s⁻¹ and 0.8 mM, respectively, providing a catalytic efficiency (k _cat/K _m) of 6.9 × 10⁵ M⁻¹ s⁻¹. The ArgE dissociation constant (K _d) for Mn(II) was determined to be 0.18 μM, correlating well with a value obtained by isothermal titration calorimetry of 0.30 μM for the first metal binding event and 5.3 μM for the second. An Arrhenius plot of the NAO hydrolysis for Mn(II)-loaded ArgE was linear from 15 to 55 °C, suggesting the rate-limiting step does not change as a function of temperature over this range. The activation energy, determined from the slope of this plot, was 50.3 kJ mol⁻¹. Other thermodynamic parameters were ΔG ^‡ = 58.1 kJ mol⁻¹, ΔH ^‡ = 47.7 kJ mol⁻¹, and ΔS ^‡ = –34.5 J mol⁻¹ K⁻¹. Similarly, plots of lnK _m versus 1/T were linear, suggesting substrate binding is controlled by a single step. The natural product, [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl]leucine (bestatin), was found to be a competitive inhibitor of ArgE with a K _i value of 67 μM. Electron paramagnetic resonance (EPR) data recorded for both [Mn(II)_(ArgE)] and [Mn(II)Mn(II)(ArgE)] indicate that the two Mn(II) ions form a dinuclear site. Moreover, the EPR spectrum of [Mn(II)Mn(II)(ArgE)] in the presence of bestatin indicates that bestatin binds to ArgE but does not form a μ-alkoxide bridge between the two metal ions.     

The mycotoxin fumonisin B1 inhibits eukaryotic protein synthesis: in vitro and in vivo studies

Inhibitory action of Fumonisin B₁ (FB₁) on eukaryotic protein synthesis was investigated, both in animal and plant system, and was compared with cycloheximide. Inhibitory effect of FB₁ was monitored in the TCA precipitable proteins of rabbit reticulocyte lysates exposed to various concentrations of the mycotoxin (0.0013–2.76 mM), using ³⁵ S-methionine as a tracer. FB₁ inhibited the protein synthesis by 6%, at 0.0013 mM and by 88%, at a higher concentration of 2.76 mM. Cycloheximide at a concentration of 0.355 mM was found to inhibit protein synthesis by 88%. Inhibitory action of FB₁ (1 mg kg⁻¹ body mass and a higher dose of 10 mg kg⁻¹ body mass) or cycloheximide (10 mg kg⁻¹ body mass; positive controls), injected intra-peritoneally into BALB/c mice was studied using ¹⁴C-l-Leucine as a tracer. FB₁ at lower dose of 1 mg kg⁻¹ body mass inhibited protein synthesis in liver by 8% and at a higher dose of 10 mg kg⁻¹ body mass by 38% in the BALB/c mice, when compared to cycloheximide which inhibited protein synthesis by 61%. The effects of FB₁ on protein synthesis in plant system was studied in germinated maize seedlings exposed to FB₁ at 0.9 μM, 0.009 mM and 0.09 mM concentrations, using ¹⁴C-l-Leucine as a tracer. Fumonisin B₁ at low, middle, and higher concentrations (0.9 μM, 0.009 mM, and 0.09 mM) inhibited protein synthesis in the seedlings by 4%, 12% and 22%, respectively. The inhibitory effects of FB₁ on the protein synthesis in the animal system in vitro and in vivo conditions, and in the plant system were found to be dose-dependent, though it was less potent compared to cycloheximide.     

In vitro regeneration of Vigna unguiculata (L.) Walp. cv. Blackeye cowpea via shoot organogenesis

An in vitro regeneration system was developed in cowpea [Vigna unguiculata (L.) Walp.] Blackeye. Among several explants studied, shoot initiation response was observed from shoot apices of 3–5-day-old seedlings. The optimal medium for maximum shoot initiation comprised MS salts, B₅ vitamins, 8.88 μM N ⁶-benzylaminopurine, 1 gl^-1 casein hydrolysate, 342 μM L-glutamine, 3% sucrose, 0.3% phytagel, adjusted to pH 5.8. A shift in pH from 5.8 to 7.0 had no effect on shoot initiation and on number of shoots per explant. The highest shoot initiation frequency (77%) was obtained using this preferred medium, reaching a maximum of eight shoots per explant. For shoot elongation, 14 μM gibberellic acid was supplemented in the shoot initiation medium. Presence of indolebutyric acid in the rooting medium had no effect on root induction. The regenerated plants were fertile and developed normally.     

Structural Revision of Sulfated Polysaccharide B-1 Isolated from a Marine <Emphasis Type="Italic">Pseudomonas</Emphasis> Species and Its Cytotoxic Activity Against Human Cancer Cell Lines

Abstract The structure of a sulfated polysaccharide (B-1) isolated and purified from the culture filtrate of marine Pseudomonas sp. WAK-1 was revised to have a repeating unit as follows: -2)-β-D-Galp(4SO₄)(1-4)[β-D-Glcp(1-6)]-β-D-Galp(3SO₄)(1-. B-1 was evaluated for anticancer activity using a human cancer cell line panel coupled with a drug sensitivity database. The average B-1 concentration required for 50% growth inhibition against the panel of 39 cell lines was 63.2 μg/ml. Among the cancer cell lines tested, high sensitivities to B-1 were observed in central nervous system cancer and lung cancer cell lines. The COMPARE analysis revealed that the differential growth inhibition pattern of B-1 had no significant correlation with those of more than 200 standard compounds, most of which were anticancer drugs and different types of inhibitors. This lack of similarities in the cytotoxic patterns appears to reflect previously unrecognized biological properties of B-1. It was revealed that B-1 induced apoptosis in U937 cells, as shown by cell morphology and internucleosomal DNA fragmentation.     

Evaluation of the maximum specific growth rate of a yeast indicating non-linear growth trends in batch culture

The maximum specific growth rate (μ_max) of an ethanolic D-xylose-fermenting yeast, Pichia stipitis, showing non-linear growth trends in batch culture, was calculated using the rate equation μ₂ = (1/Δt) ln(x ₂/x ₁). The absolute error Δμ, affecting μ₂, was derived using an equation given by Borzani (1994). Based on the assumption of linearity of growth curves between two closest time points, the relation between the two rate formulae, μ₁ = (1/xˉ)dx _t /dt and μ₂ = (1/Δt) ln(x ₂/x ₁) was established. In a particular condition, when μ₁ = μ₂, an equation has been developed, the roots of which are the specific growth rates at different time points. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of salinity on chlorophyll fluorescence and CO<Subscript>2</Subscript> fixation in C<Subscript>4</Subscript> estuarine grasses

The effects of salinity (sea water at 0 ‰ versus 30 ‰) on gross rates of O₂ evolution (J _O2) and net rates of CO₂ uptake (P _N) were measured in the halotolerant estuarine C₄ grasses Spartina patens, S. alterniflora, S. densiflora, and Distichlis spicata in controlled growth environments. Under high irradiance, salinity had no significant effect on the intercellular to ambient CO₂ concentration ratio (C _i/C _a). However, during photosynthesis under limiting irradiance, the maximum quantum efficiency of CO₂ fixation decreased under salinity across species, suggesting there is increased leakage of the CO₂ delivered to the bundle sheath cells by the C₄ pump. Growth under salinity did not affect the maximum intrinsic efficiency of photosystem 2, PS2 (F_V/F_M) in these species, suggesting salinity had no effect on photosynthesis by inactivation of PS2 reaction centers. Under saline conditions and high irradiance, P _N was reduced by 75 % in Spartina patens and S. alterniflora, whereas salinity had no effect on P _N in S. densiflora or D. spicata. This inhibition of P _N in S. patens and S. alterniflora was not due to an effect on stomatal conductance since the ratio of C _i/C _a did not decrease under saline conditions. In growth with and without salt, P _N was saturated at ∼500 μmol(quantum) m⁻² s⁻¹ while J _O2 continued to increase up to full sunlight, indicating that carbon assimilation was not tightly coupled to photochemistry in these halophytic species. This increase in alternative electron flow under high irradiance might be an inherent function in these halophytes for dissipating excess energy.     

Plant regeneration and Agrobacterium-mediated transformation of cotyledon explants of Citrullus colocynthis (L.) Schrad.

The effect of 6-benzylaminopurine (6-BA) alone or in combination with naphthaleneacetic acid or indoleacetic acid on the morphogenetic response of cotyledon explants of Citrullus colocynthis (L.) Schrad. was tested. The best results were obtained with a medium containing 25 μm 6-BA, which yielded organogenic calli at a frequency of 81.8%. When these organogenic calli were transferred to elongation medium (basal medium supplemented with 0.5 μm 6-BA), 80% produced well-developed shoots. These shoots rooted normally when cultured on rooting medium containing indolebutyric acid at 2.5 or 5.0 μm. Plants grew to maturity under greenhouse conditions and gave normal fruits. Cotyledon explants were transformed by cocultivation with Agrobacterium tumefaciens LBA4404 carrying the binary vector pBI121 which bears the reporter gene β-glucuronidase (gus) and the marker gene neomycin phosphotransferase (nptII). Transformants were selected for growth capacity on medium with 100 mgl^–1 of kanamycin. On the basis of β-glucuronidase expression, the transformation frequency was 14.2%. Molecular characterization by polymerase chain reaction confirmed the presence of the two genes transferred (gus, nptII) in the transgenic plants. Sexual transmission of both genes was also confirmed by studying their expression in progenies from several transgenic plants. Received: 9 May 1996 / Revision received: 3 December 1996 / Accepted: 20 January 1997     

Intrinsic changes in photosynthetic parameters of carrot leaves under increasing CO<Subscript>2</Subscript> concentrations and soil moisture regimes

A controlled growth chamber experiment was conducted to investigate the short-term water use and photosynthetic responses of 30-d-old carrot seedlings to the combined effects of CO₂ concentration (50–1 050 μmol mol⁻¹) and moisture deficits (−5, −30, −55, and −70 kPa). The photosynthetic response data was fitted to a non-rectangular hyperbola model. The estimated parameters were compared for effects of moisture deficit and elevated CO₂ concentration (EC). The carboxylation efficiency (α) increased in response to mild moisture stress (−30 kPa) under EC when compared to the unstressed control. However, moderate (−55 kPa) and extreme (−70 kPa) moisture deficits reduced α under EC. Maximum net photosynthetic rate (P _Nmax) did not differ between mild water deficit and unstressed controls under EC. Moderate and extreme moisture deficits reduced P _Nmax by nearly 85 % compared to controls. Dark respiration rate (R _D) showed no consistent response to moisture deficit. The CO₂ compensation concentration (Γ) was 324 μmol mol⁻¹ for −75 kPa and ranged 63–93 μmol mol⁻¹ for other moisture regimes. Interaction between moisture deficit and EC was noticed for P _N, ratio of intercellular and ambient CO₂ concentration (C _i/C _a), stomatal conductance (g _s ), and transpiration rate (E). P _N was maximum and C _i/C _a was minimum at −30 kPa moisture deficit and at C _a of 350 μmol mol⁻¹. The g _s and E showed an inverse relationship at all moisture deficit regimes and EC. Water use efficiency (WUE) increased with moisture deficit up to −55 kPa and declined thereafter. EC showed a positive influence towards sustaining P _N and increasing WUE only under mild moisture stress, and no beneficial effects of EC were noticed at moderate or extreme moisture deficits.     

Phytoplankton primary production in a mesotrophic pond in sub-tropical Bangladesh

Annual gross primary productivity in mesotrophic Shahidullah Hall pond (Dhaka, Bangladesh) was 1383.35 g C m⁻² y⁻¹ (arithmetic mean). Daily primary productivity (between 1.6 and 6.8 g C m⁻² d⁻¹ was correlated with chlorophylla, day length and dissolved silica. Chlorophylla related significantly withk, incident light, SRP, alkalinity and conductivity. A negative correlation existed between biomass and rainfall. Productivity, biomass, conductivity, alkalinity, and SRP increased after mid-winter.k, I _k andZ _eu varied according seasonally.P _max related directly with temperature. Seasonal variation of ∝ ^B was 0.0049–0.0258 mg C (mg chla mmol PAR)⁻¹ m⁻². Q₁₀ was 2.12, community respiration 1334.99 g C m⁻² y⁻¹, and the underwater light climate 186.43μE m⁻² s⁻¹.     

Partitioning of photosynthetic electron flow between CO<Subscript>2</Subscript> assimilation and O<Subscript>2</Subscript> reduction in sunflower plants under water deficit

In sunflower (Helianthus annuus L.) grown under controlled conditions and subjected to drought by withholding watering, net photosynthetic rate (P _N) and stomatal conductance (g _s) of attached leaves decreased as leaf water potential (Ψ_w) declined from −0.3 to −2.9 MPa. Although g _s decreased over the whole range of Ψ_w, nearly constant values in the intercellular CO₂ concentrations (C _i) were observed as Ψ_w decreased to −1.8 MPa, but C _i increased as Ψ_w decreased further. Relative quantum yield, photochemical quenching, and the apparent quantum yield of photosynthesis decreased with water deficit, whereas non-photochemical quenching (q_NP) increased progressively. A highly significant negative relationship between q_NP and ATP content was observed. Water deficit did not alter the pyridine nucleotide concentration but decreased ATP content suggesting metabolic impairment. At a photon flux density of 550 μmol m⁻² s⁻¹, the allocation of electrons from photosystem (PS) 2 to O₂ reduction was increased by 51 %, while the allocation to CO₂ assimilation was diminished by 32 %, as Ψ_w declined from −0.3 to −2.9 MPa. A significant linear relationship between mean P _N and the rate of total linear electron transport was observed in well watered plants, the correlation becoming curvilinear when water deficit increased. The maximum quantum yield of PS2 was not affected by water deficit, whereas q_P declined only at very severe stress and the excess photon energy was dissipated by increasing q_NP indicating that a greater proportion of the energy was thermally dissipated. This accounted for the apparent down-regulation of PS2 and supported the protective role of q_NP against photoinhibition in sunflower.     

Compensatory effects of elevated CO<Subscript>2</Subscript> concentration on the inhibitory effects of high temperature and irradiance on photosynthetic gas exchange in carrots

We determined the interactive effects of irradiance, elevated CO₂ concentration (EC), and temperature in carrot (Daucus carota var. sativus). Plants of the cv. Red Core Chantenay (RCC) were grown in a controlled environmental plant growth room and exposed to 3 levels of photosynthetically active radiation (PAR) (400, 800, 1 200 μmol m⁻² s⁻¹), 3 leaf chamber temperatures (15, 20, 30 °C), and 2 external CO₂ concentrations (C _a), AC and EC (350 and 750 μmol mol⁻¹, respectively). Rates of net photosynthesis (P _N) and transpiration (E) and stomatal conductance (g _s ) were measured, along with water use efficiency (WUE) and ratio of internal and external CO₂ concentrations (C _i/C _a). P _N revealed an interactive effect between PAR and C _a. As PAR increased so did P _N under both C _a regimes. The g _s showed no interactive effects between the three parameters but had singular effects of temperature and PAR. E was strongly influenced by the combination of PAR and temperature. WUE was interactively affected by all three parameters. Maximum WUE occurred at 15 °C and 1 200 μmol m⁻² s^{− 1} PAR under EC. The C _i /C _a was influenced independently by temperature and C _a. Hence photosynthetic responses are interactively affected by changes in irradiance, external CO₂ concentration, and temperature. EC significantly compensates the inhibitory effects of high temperature and irradiance on P _N and WUE.     

Chromium-induced glucose uptake, superoxide anion production, and phagocytosis in cultured pulmonary alveolar macrophages of weanling pigs

The dose-dependent effects of chromium chloride (CrCl₃) and chromium picolinate (CrPic) were evaluated for their glucose uptake, superoxide anion (O ₂ ⁻ ) production, activity of glucose-6-phosphate dehydrogenase, and phagocytosis of incubated pulmonary alveolar macrophages in medium containing no or 5 × 10⁻⁸ M insulin. Glucose uptake was found to increase in cells treated with 20 μg/L CrCl₃. Incubation with 20 μg/L of CrPic enhanced glucose uptake and O ₂ ⁻ production in an insulin-dependent manner. However, the inclusion of CrPic to 100 μg/L in the medium absent of insulin also increased O ₂ ⁻ production. The activity of glucose-6-phosphate dehydrogenase was not affected by either the addition of Cr or insulin. The phagocytosis of Escherichia coli by macrophages was enhanced significantly (p<0.05) in medium containing 10–100 μg/L CrCl₃ or 20–100 μg/L CrPic in the presence of insulin. These results suggest that the addition of 10–20 μg/L CrCl₃ enhances directly the cellular activity of macrophages, whereas the effect of CrPic requires the cooperative action of insulin in enhancing their glucose uptake and phagocytosis.     

Photosystem 2 photochemistry and pigment composition of a yellow mutant of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) under different irradiances

A yellow leaf colouration mutant (named ycm) generated from rice T-DNA insertion lines was identified with less grana lamellae and low thylakoid membrane protein contents. At weak irradiance [50 μmol(photon) m⁻² s⁻¹], chlorophyll (Chl) contents of ycm were ≈20 % of those of WT and Chl a/b ratios were 3-fold that of wild type (WT). The leaf of ycm showed lower values in the actual photosystem 2 (PS2) efficiency (Φ_PS2), photochemical quenching (q_P), and the efficiency of excitation capture by open PS2 centres 1 (F_v′/F_m′) than those of WT, except no difference in the maximal efficiency of PS2 photochemistry (F_v/F_m). With progress in irradiance [100 and 200 μmol(photon) m⁻² s⁻¹], there was a change in the photosynthetic pigment stoichiometry. In ycm, the increase of total Chl contents and the decrease in Chl a/b ratio were observed. Φ_PS2, q_P, and F_v′/F_m′ of ycm increased gradually along with the increase of irradiance but still much less than in WT. The increase of xanthophyll ratio [(Z+A)/(V+A+Z)] associated with non-photochemical quenching (q_N) was found in ycm which suggested that ycm dissipated excess energy through the turnover of xanthophylls. No significant differences in pigment composition were observed in WT under various irradiances, except Chl a/b ratio that gradually decreased. Hence the ycm mutant developed much more tardily than WT, which was caused by low photon energy utilization independent of irradiance.     

Seasonal changes in the photosynthetic capacity of cones on a larch (Larix kaempferi) canopy

The seasonal changes of photosynthesis of cones of Japanese larch (Larix kaempferi Carr.) trees showed that gross photosynthetic rate of young cones (P _G) was 2–3 μmol m⁻² s⁻¹ at surface area unit and P _G/R _D (dark respiration of cones) peaked about 0.7 in the same period, indicating that 70 % of respiratory CO₂ was re-fixed. With maturation, P _G and P _G/R _D sharply decreased. Chlorophyll content in cones was 3–20 % of that in leaves, which made it a limiting factor for photosynthesis and its content was closely correlated with photosynthetic capacity. Although sunken and linearly arranged stomatal organs were found on the scale of young cones, differently from the significant regulation of leaf photosynthesis, these stomata tended to be non-functional since CO₂ is not limiting factor for cone photosynthesis. Thus photosynthesis of larch cones is an additional contribution to their development.     

Carbon-nanotube-modified electrodes for the direct bioelectrochemistry of pseudoazurin

The bioelectrochemistry of the blue copper protein, pseudoazurin, at glassy carbon and platinum electrodes that were modified with single-wall carbon nanotubes (SWNTs) was investigated by multiple scan rate cyclic voltammetry. The protein showed reversible electrochemical behavior at both bare glassy carbon electrodes (GCEs) and SWNT-modified GCEs (SWNT|GCEs); however, direct electrochemistry was not observed at any of the platinum electrodes. The effect of the carbon nanotubes at the GCE was to amplify the current response 1000-fold (nA at bare GCE to μA at SWNT|GCE), increase the apparent diffusion coefficient D _app of the solution-borne protein by three orders of magnitude, from 1.35 × 10⁻¹¹ at bare GCE to 7.06 × 10⁻⁸ cm² s-1 at SWNT|GCE, and increase the heterogeneous electron transfer rate constant k _s threefold, from 1.7 × 10⁻² cm s⁻¹ at bare GCE to 5.3 × 10⁻² cm s⁻¹ at SWNT|GCE. Pseudoazurin was also found to spontaneously adsorb onto the nanotube-modified GCE surface. Well-resolved voltammograms indicating quasi-reversible faradaic responses were obtained for the adsorbed protein in phosphate buffer, with I _pc and I _pa values now greater than corresponding values for solution-borne pseudoazurin at SWNT|GCEs and with significantly reduced ΔE _p values. The largest electron transfer rate constant of 1.7 × 10⁻¹ cm s⁻¹ was achieved with adsorbed pseudoazurin at the SWNT|GCE surface in deaerated buffer solution consistent with its presumed role in anaerobic respiration of some bacteria.     

Microcalorimetric studies of the action of Na2SeO3 on the growth of Halobacterium halobium R1

The effect of Na₂SeO₃ on the growth of Halobacterium halobium R1 was investigated by means of microcalorimetry at 37°C. The biological response to toxicants is observed as the inhibition of the rate constant of growth of living cells. A low concentration of Na₂SeO₃ stimulated the growth of H. halobium R1, and a high concentration of Na₂SeO₃ inhibited the growth of H. halobium R1. Toxicity may be expressed as the half-inhibition concentration (IC₅₀). The rate constants of growth (k) and the concentrations of Na₂SeO₃ (c) shows a linear relationship: k=1.790 × 10⁻⁶ − 2.27 × 10⁻³ c. The value of IC₅₀ obtained from the accompanying figure of I-c is 679 μg/mL.     

A new model for relationship between irradiance and the rate of photosynthesis in <Emphasis Type="Italic">Oryza sativa</Emphasis>

The calculated maximum net photosynthetic rate (P _N) at saturation irradiance (I _m) of 1 314.13 μmol m⁻² s⁻¹ was 25.49 μmol(CO₂) m⁻² s⁻¹, and intrinsic quantum yield at zero irradiance was 0.103. The results fitted by nonrectangular hyperbolic model, rectangular hyperbolic method, binomial regression method, and the new model were compared. The maximum P _N values calculated by nonrectangular hyperbolic model and rectangular hyperbolic model were higher than the measured values, and the I _m calculated by nonrectangular hyperbolic model and rectangular hyperbolic model were less than measured values. Results fitted by new model showed that the response curve of P _N to I was nonlinear at low I for Oryza sativa, P _N increased nonlinearly with I below saturation value. Above this value, P _N decreased nonlinearly with I.