Patterns of energy storage in Pseudoboeckella poppei (Crustacea,copepoda) from two contrasting lakes on Signy Island,Antarctica

The copepod Pseudoboeckella poppei (Daday) (Calanoida, Centropagidae) was sampled from Sombre and Heywood Lakes on Signy Island, Antarctica (60° S, 45° W) between January 1984 and March 1985. Sombre Lake is clear and oligotrophic with little phytoplankton and a bottom sediment low in organic content. By contrast Heywood Lake is turbid and mesotrophic; a substantial phytoplankton develops in summer and the bottom sediments are comparatively rich in organics. Both lakes freeze over for much of the year, forcing the copepods to adopt a benthic feeding strategy over winter. Adult Pseudoboeckella feed on phytoplankton when this is available, but also on detritus, diatoms and short algal filaments stirred up from the sediment. In Heywood Lake, male copepods show a smooth seasonal trend in lipid content with lipid being synthesised in early summer and utilised in late summer and winter. The summer increase in lipid content is associated with an increase in dry weight. Female lipid contents show evidence of two peaks of egg production. In Sombre Lake both male and female copepods increase in size during summer and show a wider range of lipid contents than in Heywood Lake; it is likely that this is due to the poorer winter feeding conditions which necessitate the synthesis of a much larger store of reserves during the summer. In contrast to marine calanoid copepods, lipid stores are exclusively triacylglycerol with no trace of wax ester.     

Effects of wearing two different types of clothing on body temperatures during and after exercise

The experiment was conducted to investigate the human thermoregulatory responses during rest, exercise and recovery atT _a 20°C and 60% R.H. under the conditions of wearing two different types of clothing. Six healthy men wore two types of clothing: one covering the whole body area except the head (Type A, weight 1656 g), and the other covering only the trunk, upper arms and thighs (Type B, weight 996 g). The level of rectal temperature was kept significantly higher in Type B than in Type A during rest and recovery. The increased and decreased rates of rectal temperature during exercise and recovery were significantly greater in Type A than in Type B, respectively. These findings are discussed from the viewpoint of the differences of skin temperatures of the extremities between Type A and Type B.     

Large scale protein separations: engineering aspects of chromatography

The engineering considerations common to large scale chromatographic purification of proteins are reviewed. A discussion of the industrial chromatography fundamentals is followed by aspects which affect the scale of separation. The separation column geometry, the effect of the main operational parameters on separation performance, and the physical characteristics of column packing are treated. Throughout, the emphasis is on ion exchange and size exclusion techniques which together constitute the major portion of commercial chromatographic protein purifications. In all cases, the state of current technology is examined and areas in need of further development are noted.

The physico-chemical advances now underway in chromatographic separation of biopolymers would ensure a substantially enhanced role for these techniques in industrial production of products of new biotechnology.     

Biological effects of synthetic AKH in Manduca sexta and estimates of the amount of AKH in corpora cardiaca

Dose-response curves were measured with synthetic Manduca adipokinetic hormone (AKH) for glycogen phosphorylase activation in larvae and for lipid mobilization in adults. Both responses are known hormonal functions in Manduca sexta. In ligated larvae, full activation of glycogen phosphorylase was achieved with 0.1 pmol and half-maximal activation with 0.03-0.04 pmol. Maximal lipid mobilization in adults required 10 pmol and half-maximal mobilization 0.15 to 0.2 pmol, respectively. An estimate of AKH content of corpora cardiaca from M. sexta was gained by comparing the dose-response curves for synthetic Manduca AKH with curves from gland extracts. Corpora cardiaca extracts were also quantitated by high performance liquid chromatography. According to both estimates corpora cardiaca of adults contain 10-20 pmol AKH per pair, while a pair of larval corpora cardiaca contains 0.7-2 pmol.     

Temperature-dependent osmotic permeability in glycoproteion containing liposomes

The osmotic water outflow of large multilamellar liposomes containing ₁-acid glycoprotein was measured at a temperature near the lipid's phase transition temperature. The liposomes were formed from a mixture of DPPC, cholesterol and glycoprotein in molar ratios 100:20:1, by continuous sucrose density gradient centrifugation. These liposomes captured 35% of the radiolabeled glycoprotein. The temperature-dependent experiments showed that near phase transition temperature the initial rate of water outflow increased drastically in comparison with glycoprotein free liposomes incubated in buffer containing glycoprotein. We suggested that eventual a channel mechanism may be involved due to spontaneous incorporation of glycoprotein into the bilayer.     

In vitro and ex vivo effects of antidepressants on rat brain membrane-bound phosphatidylinositol synthetase activity

The in vitro and ex vivo effects of antidepressant drugs on membrane-bound phosphatidylinositol (PI) synthetase and PI: myo-inositol exchange enzyme activities were examined. In rat brain subcellular fractions, PI synthetase occurred exclusively in the microsomes. In comparison, the activity of CDP-diglyceride independent PI: myo-inositol exchange enzyme was low (3%). Of the various CDP-diglycerides tested for the activation of PI synthetase, CDP-dipalmitin was the most active. Addition of 1 mM of desipramine, amitriptyline, imipramine, iprindole, clomipramine and mianserin in vitro significantly inhibited (30–60%) PI synthetase activity, whereas the same concentration of zimelidine and fluoxetine had no effect. At low liponucleotide concentrations, PI synthetase activity was significantly enhanced by imipramine (1 mM), whereas the enzyme activity was inhibited at higher liponucleotide concentrations (>0.3 mM). In contrast, imipramine had no effect on the PI: myo-inositol exchange enzyme activity. No significant alteration in the PI synthetase activity was found following either acute (2 h) or chronic (21 d) treatment of rats with imipramine. The above results indicate that the de novo synthesis of PI is inhibited in vitro but not ex vivo by some antidepressant drugs. However, in view of the high concentration of the drugs required, the pharmacological significance of this inhibitory action with respect to their therapeutic effects is doubtful.     

In vitro tuberization in white yam (Dioscorea rotundata Poir)

Nodal cuttings of white yam were induced to produce microtubers on a MS-revised medium supplemented with various concentrations of sucrose, 20 mgl^–1 L-cysteine, 0.5 mgl^–1 kinetin and 0.7% agar. The frequency of tuberization was affected by the daylength, which is optimal at 12 and 16 h of light depending on the sucrose concentration. The microtubers were planted in a seed bed and grown to maturity. The importance of in vitro tuberization of yam as a means of international germplasm distribution or exchange as well as for the propagation of planting material is discussed.     

A laser-T-jump study of the adsorption of dipolar molecules to planar lipid membranes

The adsorption of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) as well as of other dipolar molecules to the interface of artificial lipid membranes gives rise to a change of the dipole potential between the membrane interior and water. As a consequence of the adsorption of the neutral species, the conductance of planar membranes, observed in the presence of the macrocyclic ion carriers nonactin or valinomycin, may change by many orders of magnitude. Using this effect in combination with a laser-T-jump technique, the kinetics of the adsorption process were measured and were interpreted on the basis of a Langmuir-isotherm. A partition coefficient (at small concentrations) of _HA =4.7·10^–4 cm, a rate constant of desorption k _HA100 s^-1 and a maximum surface density N _D=7.7·10¹³/cm² were found. The concentration at half saturation is K _HA=2.7·10^-4 M.Using these values the membrane conductance induced by the ion carrier nonactin and the shape of the current-voltage relationship as a function of the ligand concentration in water was analyzed. A maxiumum dipole potential of V _D ^max =-239 m V and a contribution of b=3.1·10^-15V cm² per single adsorbed 2,4-D molecule was found. 74% of the dipole potential acts on the inner membrane barrier separating the two interfacial adsorption planes of nonactin. The remainder (26%) favours interfacial complex formation between nonactin and K⁺ from the aqueous phase. The data hold for membranes formed from dioleoyllecithin in n-decane.     

Calcium ion transport across discs of the cortical flesh of apple fruit in relation to fruit development

Transport of Ca²⁺ through discs of apple fruit tissue was examined in tissue taken at different stages of fruit development. Transport rates decreased with fruit development when cation exchange was the predominant influence on transport (with 10⁻⁶ M ⁴⁵CaCl₂ as the source solution). This decrease was associated with a reduction in relative cell wall surface area, cation exchange capacity and cell wall yield that occurred during fruit growth. When diffusion was the major transport force, and when transport was influenced by solution infiltration of the tissue disc (10⁻² M ⁴⁵CaCl₂ in the source solution), transport rates increased during fruit growth. This increment was related to increases in air space of the tissue. Ca²⁺ transport through apple fruit tissue is influenced by the extent and nature of the cell wall, changing proportions of air space and Ca²⁺ concentration in the extracellular solution.     

Gating properties of channels formed by colicin Ia in planar lipid bilayer membranes

Summary Colicin Ia forms voltage-dependent channels when incorporated into planar lipid bilayers. A membrane containing many Colicin Ia channels shows a conductance which is turned on when high positive voltages (>+10 mV) are applied to thecis side (side to which the protein is added). The ionic current flowing through the membrane in response to a voltage step shows at first an exponential and then a linear rise with time. The relationship between the steady-state conductance, achieved immediately after the exponential portion, and voltage is S-shaped and is adequately fit by a Boltzmann distribution. The time constant () of the exponential is also dependent on voltage, and the relation between these two parameters is asymmetric aroundV _o (voltage at which half of the channels are open). In both cases the steepness of the voltage dependence, a consequence of the number of effective gating particles (n) present in the channel, is greatly influenced by the pH of the bathing solutions. Thus, increasing the pH leads to a reduction inn, while acidic pH's have the opposite effects. This result is obtained either by changing the pH on both sides of the membrane or on only one side, be itcis orrans. On the other hand, changing pH on only one side by addition of an impermeant buffer fails to induce any change inn. At the single-channel level, pH had an effect both on the unitary conductance, doubling it in going from pH 4.5 to 8.2, as well as on the fraction of time the channels stay open,F _(v). For a given voltage,F _(v) is clearly diminished by increasing the pH. This titration of the voltage sensitivity leads to the conclusion that gating in the Colicin Ia molecule is accomplished by charged amino-acid residues present in the protein molecule. Our results also support the notion that these charged groups are inside the aqueous portion of the channel.