THE PROBABILITY OF FIXATION OF A NEW KARYOTYPE IN A CONTINUOUS POPULATION

We investigate the probability of fixation of a chromosome rearrangement in a subdivided population, concentrating on the limit where migration is so large relative to selection (m ? s) that the population can be thought of as being continuously distributed. We study two demes, and one- and two-dimensional populations. For two demes, the probability of fixation in the limit of high migration approximates that of a population with twice the size of a single deme: migration therefore greatly reduces the fixation probability. However, this behavior does not extend to a large array of demes. Then, the fixation probability depends primarily on neighborhood size (Nb), and may be appreciable even with strong selection and free gene flow (≈exp(-B ≈ Nb√s) in one dimension, ≈exp(-B ≈ Nb) in two dimensions). Our results are close to those for the more tractable case of a polygenic character under disruptive selection.     

“Action potentials” in NEUROSPORA CRASSA, a mycelial fungus

Occasional spontaneous “action potentiais” are found in mature hyphae of the fungus Neurospora crassa. They can arise either from low-level sinusoidal oscillations of the membrane potential or from a linear slow depolarization which accelerates into a rapid upstroke at a voltage 5–20 mV depolarized from the normal resting potential (near − 180 mV). The “action potentiais” are long-lasting, 1–2 min and at the peak reach a membrane potential near −40 mV. A 2− to 8−fold increase of membrane conductance accompanies the main depolarization, but a slight decrease of membrane conductance occurs during the slow depolarization. Two plausible mechanisms for the phenomenon are (a) periodic increases of membrane permeability to inorganic ions, particularly H⁺ or Cl^- and (b) periodic decreases in activity of the major electrogenic pump (H⁺) of the Neurospora membrane, coupled with a nonlinear (inverse sigmoid) current-voltage relationship.Identification of action potential-like disturbances in fungi means that such behavior has now been found in all major biologic taxa which have been probed with suitable electrodes. As yet there is no obvious function for the events in fungi.     

Progesterone receptor associated with the “melanosome” fraction of Pleurodeles waltlii oocytes (urodela amphibian)

A proteinaceous receptor associated with the melanosome fraction of Pleurodeles waltlii oocytes binds progesterone with high affinity and limited capacity (K_D ≈ 5 · 10⁻⁸ M).     

Acid dissociation constants and pH values for standard “bes” and “tricine” buffer solutions in 30, 40, and 50 mass% dimethyl sulfoxide/water between 25 and −25 °C

Information is given concerning two standard buffer solutions suitable as pH references in 30, 40, and 50 mass% dimethyl sulfoxide (DMSO)/H₂O mixed solvents at subzero temperatures from −20 to 0 °C, with the intention of establishing a pH (designated pH^*) scale. The two buffers selected were the ampholytes N,N-bis(2-hydroxyethyl)-2-aminoethane sulfonic acid (“bes”) and N-tris(hydroxymethyl)methylglycine (“tricine”), and the reference standard consisted of equal molal quantities of the buffer and its respective sodium salt. The assignment of pH^* values was based on measurements of the emf of cells without liquid junction of the type: Pt;H₂(g,1 atm) ¦Bes, Na Besate, NaCl ¦ AgCl;Ag and Pt;H₂(g,1 atm) ¦Tricine, Na Tricinate, NaCl ¦AgCl;Ag and the pH^* was derived from a determination of K₂, the equilibrium constant for the dissociation process (Buffer)^±/ai (Buffer)⁻ + H⁺.     

Cellular “bauplans”: Evolving unicellular forms by means of Julia sets and Pickover biomorphs

The universe of cellular forms has received scarce attention by mainstream neo-Darwinian views. The possibility that a fundamental trait of biological order may consist upon, or be guided by, developmental processes not completely amenable to natural selection was more akin to previous epochs of biological thought, i.e. the “bauplan” discussion. Thirty years ago, however, Lynn and Tucker studied the biological mechanisms responsible for defining organelles position inside cells. The fact that differentiated structures performing a specific function within the eukaryotic cell (i.e. mitochondrion, vacuole, or chloroplast) were occupying specific positions in the protoplasm was the observational and experimental support of the ‘morphogenetic field’ notion at the cellular level. In the present paper we study the morphogenetic field evolution yielding from an initial population of undifferentiated cells to diversified unicellular organisms as well as specialized eukaryotic cell types. The cells are represented as Julia sets and Pickover biomorphs, simulating the effect of Darwinian natural selection with a simple genetic algorithm. The morphogenetic field “defines” the locations where cells are differentiated or sub-cellular components (or organelles) become organized. It may be realized by different possibilities, one of them by diffusing chemicals along the Turing model. We found that Pickover cells show a higher diversity of size and form than those populations evolved as Julia sets. Another novelty is the way that cellular organelles and cell nucleus fill in the cell, always in dependence on the previous cell definition as Julia set or Pickover biomorph. Our findings support the existence of specific attractors representing the functional and stable form of a differentiated cell—genuine cellular bauplans. The configuration of the morphogenetic field is “attracted” towards one or another attractor depending on the environmental influences as modeled by a particular fitness function. The model promotes the classical discussions of D’Arcy Thompson and the more recent views of Waddington, Goodwin and others that consider organisms as dynamical systems that evolve through a ‘master plan’ of transformations, amenable to natural selection. Intriguingly, the model also connects with current developments on mechanobiology, highlighting the informational–developmental role that cytoskeletons may play.     

Normal acid behavior for C(α)-proton transfer from a thiazolium lon

Rate constants for C(α)-proton transfer from racemic 2-(1-hydroxyethyl)-3,4-dimethylthi-oazolium ion catalyzed by lyoxide ion and various oxygen-containing and amine buffers were determined by iodination at 25°C and ionic strength 1.0 in H₂O. Thermodynamically unfavorable C(α)-proton transfer to oxygen-containing and amine bases shows general base catalysis with a Brønsted β value of ≥0.92 for bases of pK_a^′ ≤ 15; this indicates that the thermodynamically favorable protonation reaction in the reverse direction has a Brønsted α value ≤0.08, which is consistent with diffusion-controlled reprotonation of the C(α)-enamine by most acids. General base catalysis is detectable because there is an 85-fold negative deviation from the Brønsted correlation by hydroxide ion. Primary kinetic isotope effects of (k_H/k_D)_obsd = 1.0 for thermodynamically unfavorable proton transfer to buffer bases and hydroxide ion (ΔpK_a ≤ −6) and a secondary solvent isotope effect of k_DO⁻/k_HO⁻ = 2.3 for C(α)-proton transfer are consistent with a very late, enamine-like transition state and rate-limiting diffusional separation of buffer acids from the C(α)-enamine in the rate-limiting step, as expected for a “normal” acid. The second-order rate constants for catalysis by buffer bases were used to calculate a pK_a^′ of 21.8 for the C(α)-proton assuming a rate constant of 3 × 10^{9 −1} s⁻¹ for the diffusion-controlled reprotonation of the C(α)-enamine by buffer acids in the reverse direction. It is concluded (i) that C(α)-proton removal occurs at the maximum possible rate for a given equilibrium constant, and (ii) that C(α)-enamines can have a significant lifetime in aqueous solution and on thiamin diphosphate-dependent enzymes.     

Direct oxidation of boronates by peroxynitrite: Mechanism and implications in fluorescence imaging of peroxynitrite

In this study, we show that boronates, a class of synthetic organic compounds, react rapidly and stoichiometrically with peroxynitrite (ONOO⁻) to form stable hydroxy derivatives as major products. Using a stopped-flow kinetic technique, we measured the second-order rate constants for the reaction with ONOO⁻, hypochlorous acid (HOCl), and hydrogen peroxide (H₂O₂) and found that ONOO⁻ reacts with 4-acetylphenylboronic acid nearly a million times (k = 1.6 × 10⁶ M^− 1 s^− 1) faster than does H₂O₂ (k = 2.2 M^− 1 s^− 1) and over 200 times faster than does HOCl (k = 6.2 × 10³ M^− 1 s^− 1). Nitric oxide and superoxide together, but not alone, oxidized boronates to the same phenolic products. Similar reaction profiles were obtained with other boronates. Results from this study may be helpful in developing a novel class of fluorescent probes for the detection and imaging of ONOO⁻ formed in cellular and cell-free systems.     

In situ measurement of fine root water absorption in three temperate tree species—Temporal variability and control by soil and atmospheric factors

Miniature heat balance-sap flow gauges were used to measure water flows in small-diameter roots (3–4 mm) in the undisturbed soil of a mature beech–oak–spruce mixed stand. By relating sap flow to the surface area of all branch fine roots distal to the gauge, we were able to calculate real time water uptake rates per root surface area (J_s) for individual fine root systems of 0.5–1.0 m in length. Study aims were (i) to quantify root water uptake of mature trees under field conditions with respect to average rates, and diurnal and seasonal changes of J_s, and (ii) to investigate the relationship between uptake and soil moisture θ, atmospheric saturation deficit D, and radiation I. On most days, water uptake followed the diurnal course of D with a mid-day peak and low night flow. Neighbouring roots of the same species differed up to 10-fold in their daily totals of J_s (<100–2000 g m⁻² d⁻¹) indicating a large spatial heterogeneity in uptake. Beech, oak and spruce roots revealed different seasonal patterns of water uptake although they were extracting water from the same soil volume. Multiple regression analyses on the influence of D, I and θ on root water uptake showed that D was the single most influential environmental factor in beech and oak (variable selection in 77% and 79% of the investigated roots), whereas D was less important in spruce roots (50% variable selection). A comparison of root water uptake with synchronous leaf transpiration (porometer data) indicated that average water fluxes per surface area in the beech and oak trees were about 2.5 and 5.5 times smaller on the uptake side (roots) than on the loss side (leaves) given that all branch roots <2 mm were equally participating in uptake. Beech fine roots showed maximal uptake rates on mid-summer days in the range of 48–205 g m⁻² h⁻¹ (i.e. 0.7–3.2 mmol m⁻² s⁻¹), oak of 12–160 g m⁻² h⁻¹ (0.2–2.5 mmol m⁻² s⁻¹). Maximal transpiration rates ranged from 3 to 5 and from 5 to 6 mmol m⁻² s⁻¹ for sun canopy leaves of beech and oak, respectively. We conclude that instantaneous rates of root water uptake in beech, oak and spruce trees are above all controlled by atmospheric factors. The effects of different root conductivities, soil moisture, and soil hydraulic properties become increasingly important if time spans longer than a week are considered.     

Hydrology of winter–spring “red tides” in Bahía de Mazatlán, Sinaloa, México

“Red tide” events are frequent and periodical in Bahía de Mazatlán, Sinaloa, México. Yet, the ones observed from 4 February to 4 June 2000, showed some distinctive features: First, the dinoflagellates Prorocentrum balticum (85%), P. mexicanum (5%), and Ceratium furca (5%), dominated the composition of the blooms; Second, the average cell abundance by date was 1.3×10⁶ cells l⁻¹, with a range of 3.5×10³ to 24,500 × 10³ cells l⁻¹, well above previous records; Third, the temperature registered at 10–20 m deep was unusually cold (19 °C), below the normal average of 21.5 °C observed over the last 10 years. Salinity was high (35.9 psu) and showed very little influence on the water density gradient. A mean thermal stratification index (TSI), of 3.4, with a maximum of 7 °C, was observed throughout the period, in spite of a weak upwelling activity and intermittent strong NW winds which were unable to break up water column stratification. Temperature fluctuations at the surface and at the bottom layers showed a 30-day periodicity, suggesting some association with the lunar cycle. To explain the characteristics of the “red tides” registered in Bahía de Mazatlán during the winter–spring period of year 2000, it is proposed that the temperature and density stratification, stabilized further by internal waves that compensated for the weak upwelling activity and provided the necessary nutrients to the surface layer, favored the persistence and intensity of the harmful algal bloom events then observed.     

Studies on fungal polysaccharide XVII. A new glucuronan “protuberic acid” produced by a fungus Kobayashi Nipponica

A water-soluble glucuronan “protuberic acid”, [α]_d²² −83.6° and purified from Kobayashia Nipponica, and its physicochemical properties were investigated.The purified protuberic acid was homogeneous as shown by zone electrophoresis, gel filtration over Sepharose 4B, and ultracentrifugation. The sedimentation coefficient was 1.8 S and its intrinsic viscosity was 1.1 dl/g. By gel filtration the molecular weight was estimated to be about 170 000. The results of periodate oxidation, methylation analysis, and partial acid hydrolysis indicated that this acidic polysaccharide has a linear structure of mainly 1,4-linkages and containing an acid-labile linkage. Reduced protuberic acid, [α]_d²² −44°, is also described.     

α-Factor inhibition of the rate of cell passage through the “start” step of cell division in Saccharomyces cerevisiae yeast: Estimation of the division delay per α-factor·receptor complex

A highly sensitive, kinetically unambiguous assay for α-factor-induced delay of cell passage through the “start” step of cell division in yeast is presented. The assay employs perfusion with periodic microscopy to monitor the bud emergence kinetics on the 20% of cells within an exponentially growing population which exist prior to the α-factor execution point of start. The t_1/2 for cell passage through start by this population of cells is 31 min in the absence of α-factor. The inhibition constant, K_I, represents the α-factor concentration which produces a 50% inhibition of this rate and is equal to 2×10⁻¹⁰M. A second assay for maximal cell division arrest by α-factor on whole populations of cells is presented. This assay shows a maximum cell division arrest time of 125±5 h at saturating α-factor, and a K₅₀ (that is, an α-factor concentration which produces a half-maximal response) of 2.5×10⁻⁸M. Both assays were performed in the effective absence of α-factor inactivation. Values of the dissociation constant K_D and total number of receptors per cell which specifically mediate cell division arrest or delay were estimated to be 2.5×10⁻⁸M and 10⁴, respectively. These estimates, along with the quantitative dose-response data for division arrest which are presented here, are consistent with each receptor·α-factor complex which is present on the cell at equilibrium producing a 43±10 s delay of cell passage through start. Surprisingly, this number is constant within twofold over the entire range of cellular division arrest responses to α-factor, that is, from a 1.9-fold inhibition of the rate of cell passage through start at 0.17 nM α-factor to a 125±5 h maximum arrest at saturating α-factor concentrations of >170 nM. The possible significance of this observation toward the mechanism of α-factor-induced cell division arrest is discussed.     

Temperature Broadening of LH2 Absorption in Glycerol Solution

In order to determine the relationship between the pigment–protein and the pigment–pigment interactions, the measurements of absorption spectra of the peripheral light-harvesting complex LH2 from the purple bacteria Rhodobacter sphaeroides solvated in glycerol/buffer solution were carried out in a wide temperature range, from 4 to 250 K. The SDFs used for simulating the temperature dependence of B800 and B850 bands were determined in a parametric form. To fit experimental spectra the overall exciton–phonon coupling had to be assumed to be weak for B850 (λ/2V ≈ 0.3, where λ is the reorganization energy and V is the nearest-neighbor dipole–dipole coupling for bacteriochlorophylls). At physiological temperatures the intermediate nuclear bath dynamics compares with the magnitude of energy gap fluctuations. Slower dynamics with κ ≈ 0.39, where κ is the ratio of the nuclear relaxation rate and the line width parameter, determines the spectral shape of B850 whilst faster modulations characterize B800 (κ ≈2.39). The static disorder for the B800 band is relatively high with the characteristic value of the inhomogeneous bandwidth Γ^inh ≈120 cm⁻¹, while for the B850 band this value is almost equal to the dipole–dipole coupling strength (Γ^inh ≈360 cm⁻¹). It has been found that the LH2 absorption spectrum is likely to be influenced by the temperature dependence of the dielectric constant of the solution in the high temperature range, when the glycerol/buffer solution is in the liquid state.     

Small-scale turbulence affects the division rate and morphology of two red-tide dinoflagellates

The effects of small-scale turbulence on two species of dinoflagellates were examined in cultures where the turbulent forces came randomly from all directions and were intermittent both spatially and temporally; much like small-scale turbulence in the ocean. With Lingulodinium polyedrum (Stein) Dodge (syn. Gonyaulax polyedra), division rate increased linearly (from 0.35 to 0.5 per day) and the mean cross-sectional area (CSA) decreased linearly (from 1100 to 750 μm²) as a function of the logarithmic increase in turbulence energy dissipation rate (). These effects were noted when values increased between 10⁻⁸ and 10⁻⁴ m² s⁻³. However, when increased to 10⁻³ m² s⁻³, division rate sharply decreased and mean CSA increased. Over the same range of , Alexandrium catenella (Wheedon and Kofoid) Balech had its division rate decrease linearly (from 0.6 to 0.45 per day) and its CSA increase linearly (from 560 to 650 μm²) as a function of the logarithmic increase in . Even at the highest examined (10⁻³ m² s⁻³), which may be unrealistically high for their ambits, both L. polyedra and A. catenella still had fairly high division rates, 0.2 and 0.45 per day, respectively. Turbulence strongly affected chain formation in A. catenella. In non-turbulent cultures, the mode was single cells (80–90% of the population), but at of 10⁻⁵ to 10⁻⁴ m² s⁻³, the mode was 8 cells per chain. At the highest (10⁻³ m² s⁻³), the mode decreased to 4 cells per chain. The vertical distributions of A. catenella populations in relation to hydrographic flow fields were studied in the summers of 1997 and 1998 in East Sound, Washington, USA (latitude 48°39′N, 122°53′W). In both summers, high concentrations of A. catenella were found as a subsurface bloom in a narrow depth interval (2 m), where both current shear and turbulence intensity were at a minimum. Other researchers have shown that A. catenella orients its swimming in shear flows, and that swimming speed increases with chain length. These responses, when combined with our observations, support a hypothesis that A. catenella actively concentrates at depths with low turbulence and shear.     

RNA Affinity for Molecular L-Histidine; Genetic Code Origins

Selection for affinity for free histidine yields a single RNA aptamer, which was isolated 54 times independently. This RNA is highly specific for the side chain and binds protonated L-histidine with 10²−10³-fold stereoselectivity and a dissociation constant (K_D) of 8–54 μM in different isolates. These histidine-binding RNAs have a common internal loop–hairpin loop structure, based on a conserved RAAGUGGGKKN_0–36 AUGUN_0–2AGKAACAG sequence. Notably, the repetitively isolated sequence contains two histidine anticodons, both implicated by conservation and chemical data in amino acid affinity. This site is probably the simplest structure that can meet our histidine affinity selection, which strengthens experimental support for a “stereochemical” origin of the genetic code.[Reviewing Editor: Niles Lehman]     

Kinetic evidence for a unique testosterone-receptor complex in 5α-reductase sufficient genital skin fibroblasts and the effects of 5α-reductase deficiency on its formation

When 5α-reductase-sufficient genital skin fibroblast (GSF) monolayers are incubated with testosterone (T), they first form androgen (A)-receptor (R) complexes that dissociate at a fast rate [k(37°C = 0.024 min⁻¹]. As T is converted to 5α-dihydrotestosterone (DHT), this population of T-R complexes is eventually replaced by one that dissociates much more slowly [k(37°C) = 0.006 min⁻¹], at a rate typical of DHT-R complexes. During the course of T to DHT conversion, one may observe a population of A-R complexes that has a linear (monophasic) intermediate dissociation rate constant [k(37°C) = 0.012 min⁻¹]; this population cannot simply reflect a mixture of T- and DHT-R complexes. The rate at which the complexes are processed from one dissociative form to the next varies with the incubation temperature and the presence or absence of serum in the medium; it also varies within and among GSF strains under apparently constant conditions. To explain these facts, we propose a model that enables the 5α-reductase enzyme to influence the processive dissociative behaviour of T-R complexes by engaging in some sort of coupling with the AR. The proposal is strengthened by a set of observations in cells with constitutive, mendelian or inhibitor-induced 5α-reductase deficiency that preclude a simple quantitative relation between A-R complex processing and the extent of T to DHT conversion.     

Physiological acclimation to light in Chara intermedia nodes

In this study we investigated the ability of Chara intermedia to acclimate to different irradiances (i.e. “low-light” (LL): 20–30 μmol photons m⁻² s⁻¹ and “high-light” (HL): 180–200 μmol photons m⁻² s⁻¹) and light qualities (white, yellow and green), using morphological, photosynthesis, chlorophyll fluorescence and pigment analysis.Relative growth rates increased with increasing irradiance from 0.016 ± 0.003 (LL) to 0.024 ± 0.005 (HL) g g⁻¹ d⁻¹ fresh weight and were independent of light quality. A growth-based branch orientation towards high-light functioning as a mechanism to protect the plant from excessive light was confirmed. It was shown that the receptor responsible for the morphological reaction is sensitive to blue-light.C. intermedia showed higher oxygen evolution (up to 10.5 (HL) vs. 4.5 (LL) nmol O₂ mg Chl⁻¹ s⁻¹), photochemical and energy-dependent Chl fluorescence quenching and a lower Fv/Fm after acclimation to HL. With respect to qP, the acclimation of the photosynthetic apparatus depended on light quality and needed the blue part of the spectrum for full development. In addition, pigment composition was influenced by light and the Chl a/Car and Antheraxanthin (A) + Zeaxanthin (Z)/Violaxanthin (V) + A + Z (DES) ratios revealed the expected acclimation behaviour in favour of carotenoid protection under HL (i.e. decrease of Chl a/Car from 3.41 ± 0.48 to 2.30 ± 0.35 and increase of DES from 0.39 ± 0.05 to 0.87 ± 0.03), while the Chl a/Chl b ratios were not significantly affected. Furthermore it was shown that morphological light acclimation mechanisms influence the extent of the physiological modifications.     

The robustness of neutral models of geographical variation

The approximation of diploid migration by gametic dispersion is studied. The monoecious, diploid population is subdivided into panmictic colonies that exchange migrants. Generations are discrete and nonoverlapping; the analysis is restricted to a single locus in the absence of selection; every allele mutates to a new allele at the same rate u. Diploid-migration models without self-fertilization and with selfing at the “random” rate (equal to the reciprocal of the deme size in each deme) are investigated; in the gametic-dispersion models, selfing occurs at the random rate. It is shown for the unbounded stepping-stone model in one and two dimensions, the circular stepping-stone model, and the island model that the probabilitities of identity in state at equilibrium for diploid migration are close to those for gametic dispersion if the mutation rate is small or the deme size is large. Explicit error bounds are presented in all the above cases. It is also proved that if the number of demes is finite and the migration matrix is arbitrary but time independent and ergodic, then in the strong-migration approximation the equilibrium and the ultimate rate and pattern of convergence of both diploid-dispersion models are close to the corresponding gametic-dispersion formulae. For the strong-migration approximation at equilibrium, migration must dominate both mutation and random drift; for the convergence results, it suffices that migration dominate random drift. All the results apply to a dioecious population if the migration pattern and mutation rate are sex independent.     

Bottlenecks to water transport in Quercus robur L.: the abscission zone and its physiological consequences

Cladoptosis, the abscission of twigs, is the main mechanism of changes in crown structure in senescing pedunculate oak (Quercus robur L.). We tested the hypotheses that abscission zones in nodes of old pedunculate oak trees reduce leaf-specific hydraulic conductance of shoots and thereby limit the stomatal conductance and assimilation.Hydraulic conductance and leaf-specific hydraulic conductance, measured with a high pressure flowmeter in 0.5–1.5 m long shoots, were significantly lower in shoots of low vigour compared to vigorous growing shoots in a 165-years-old stand in the southeast of Germany. Two types of bottlenecks to water transport could be identified in shoots of old oak trees, namely nodes and abscission zones. In young twigs, vessel diameter and vessel density in nodes with abscission zones were significantly reduced compared with internodes. In nodes without abscission zones, vessel density was significantly reduced. The reduction of hydraulic conductance was especially severe in the smallest and youngest shoots with diameters less than 2 mm. Internodes of 1–5 mm sapwood diameter had an average hydraulic conductance of 7.13×10⁻⁶±0.2×10⁻⁶ kg s⁻¹ m⁻¹ MPa⁻¹, compared to 4.54×10⁻⁶±0.3×10⁻⁶ kg s⁻¹ m⁻¹ MPa⁻¹ in those with nodes.Maximum stomatal conductance and maximum net assimilation rate increased significantly with hydraulic conductance and leaf-specific hydraulic conductance. Maximum rate of net photosynthesis A_max of the most vigorous shoots (VC0) (7.34±0.55 μmol m⁻² s⁻¹) was significantly higher (P<0.001) than in shoots of other vigour classes (5.97±0.28 μmol m⁻² s⁻¹). Our data support the hypothesis that the changes in shoot and consequently crown architecture that are observed in ageing and declining trees can limit photosynthesis by reducing shoot hydraulic conductance. Abscission zones increase the hydraulic disadvantage of less vigorous compared to vigorously growing twigs. Cladoptosis might serve as a mechanism of selection between twigs of different efficiency.     

Kinetic analyses for bindings of concanavalin A to dispersed and condensed mannose surfaces on a quartz crystal microbalance

A biotinylated mannotriose (Man3-bio) was dispersively immobilized in the matrix of biotinylated lactose (Gal-Glc-bio) on a streptavidin-covered, 27-MHz quartz crystal microbalance (QCM), and binding kinetics of concanavalin A (Con A) to Man3-bio in the Gal-Glc-bio matrix could be obtained from frequency decreases (mass increases) of the QCM. Association constants (K_a) and binding and dissociation rate constants (k_on and k_off) could be determined separately as the 1:1 and 1:2 bindings of Con A to Man3-bio on the surface. When Man3-bio was immobilized with content of 1 to 5 mol% in the matrix, the 1:1 binding of Con A to Man3-bio was obtained as K_a = (4 ± 1) × 10⁶ M⁻¹, k_on = (4 ± 1) × 10⁴ M⁻¹ s⁻¹, and k_off = (12 ± 2) × 10^–3 s⁻¹. On the contrary, when Man3-bio was immobilized with content of 20 to 100 mol% in the matrix, the 1:2 binding of Con A to Man3-bio was obtained as K_a = (14 ± 2) × 10⁶ M⁻¹, k_on = (14 ± 2) × 10⁴ M⁻¹ s⁻¹, and k_off = (7 ± 2) × 10^–3 s⁻¹. Thus, K_a for the 1:2 binding was 10 times larger than that for the 1:1 binding, with a three times larger binding rate constant (k_on) and a three times smaller dissociation rate constant (k_off). This is the first example to obtain separate kinetic parameters for the 1:1 and 1:2 bindings of lectins to carbohydrates on the surface.     

Photosynthetic characteristics of the economic brown seaweed <Emphasis Type="BoldItalic">Hizikia fusiforme</Emphasis> (Sargassaceae,Phaeophyta), with special reference to its “leaf” and receptacle

Photosynthetic responses to irradiance and temperature of “leaves” and receptacles were compared in February (vegetative stage) and May (reproductive stage) in the seaweed, Hizikia fusiforme (Harvey) Okamura (Sargassaceae, Phaeophyta) from Nanao Island, Shantou, China. Irradiance-saturated photosynthesis (P_max) was significantly higher in receptacles than in “leaves” on a fresh weight basis, and that of “leaves” was greater in May than in February at ambient seawater temperatures. The optimum temperature for P_max was 30^∘C for both “leaves” and receptacles, being 5–10^∘C higher than the ambient seawater temperature. The apparent photosynthetic efficiencies were greater in receptacles than in “leaves” within the tested temperature range of 10–40^∘C. The irradiance for saturating photosynthesis for both “leaves” and receptacles was temperature-dependent, with the highest values (about 200μmolphotonsm⁻²s⁻¹) at 30^∘C.