Gelation of xanthan with trivalent metal ions

In-situ gelation of semidilute xanthan solutions with trivalent chromium, aluminum or iron ions was studied by rheology and UV-spectroscopy. Measurements of the elastic modulus of xanthan gel cylinders prepared by dialysis against the complexing ion at pH values from 2 to 6 indicate that monomeric species of the ion are ineffective, whereas dimeric or higher oligomeric species are effective in crosslinking the polysaccharide. When chromium was used as the crosslinking species, the dependence of the gelation rate on the ionic concentration followed a power law with a coefficient of 1·7. The gelation time and the gelation rate were found to extrapolate to zero at 1 m Cr for 2·5 mg/ml xanthan. The limiting concentration of xanthan needed for gelation with 5 m Cr(III) at 20°C was estimated as 0·35 mg/ml. This critical xanthan concentration is close to the overlap concentration c^* estimated from the experimentally determined intrinsic viscosity [η] using c^* = 1·4/[η]. An apparent activation energy for crosslinking of xanthan was calculated as E_a = 42 kJ/mol and E_a = 108 kJ/mol for Cr and Al ions, respectively. The fractal dimensionality of xanthan-Cr at the sol-gel transition was estimated as 1·3 applying the Chambon-Winter criterion for gelation, thus indicating that this gelation criterion is applicable also to stiff-chain polysaccharides such as xanthan.     

铬离子对蛹虫草子实体生物量及化学成分的影响

蛹虫草是一种具有多种生物功能的药用真菌,近年来在金属离子富集方面受到学者的广泛关注,但对蛹虫草富集Cr³⁺的能力及其相应的生理反应尚无文献报道。为此,本研究利用含有不同Cr³⁺浓度的燕麦培养基培养蛹虫草子实体,分别对蛹虫草子实体生物量及子实体中虫草素、腺苷、虫草酸、麦角甾醇、铬离子含量等指标进行了测定。结果表明,除麦角甾醇随着培养基中Cr³⁺浓度的增加而降低之外,其余指标均呈现先增加后降低的变化趋势。700 mg/L Cr³⁺处理时,子实体干、鲜重和铬离子含量达到最大值,分别比对照组增加36.85%、35.53%和202.12%;当Cr³⁺达1 500 mg/L时,虫草素和腺苷含量达到最大值,分别比对照组高94.61%和530.29%;虫草酸含量和多糖含量分别在1 100 mg/L和1 200 mg/L Cr³⁺处理时达到最大值,分别比对照组高123.62%和21.39%。本研究首次探讨了蛹虫草子实体富集Cr³⁺的能力以及Cr³⁺处理下的子实体生物量和部分次生代谢产物含量的变化规律,为进一步研究蛹虫草富集铬离子机制提供了理论依据,为富铬蛹虫草功能性食品的研发奠定了基础。     

Cr3+,Cr6+及其复合污染对狐尾藻的毒害作用

采用急性毒害水培法,研究比较了不同浓度的Cr⁶⁺,Cr³⁺单一及复合处理对狐尾藻不定根和叶片生理生态的影响。实验结果表明:1)当浓度≤1mg·L^-1时,Cr³⁺对不定根的生长表现出促进作用,数量增加,长度增长。而Cr⁶⁺及复合处理系列对不定根却表现出强烈的抑制作用,在高浓度时甚至使其生长停止;2)叶绿素含量在1mg·L^-1Cr³⁺培养液中达到最大值,随Cr⁶⁺及复合处理浓度的增大而呈连续下降趋势;3)可溶性蛋白含量在三种处理方式中都表现出抛物线形式,复合处理组在1mg·L^-1时使蛋白含量出现高峰;4)细胞内超氧阴离子产生速率,膜脂过氧化水平与污染浓度和时间呈显著正相关;5)随着处理浓度的增加,SOD,OD,CAT活性先升后降,但其高峰分别出现在处理浓度为1mg·L^-1,10mg·L^-1,5mg·L^-1时;6)研究证实,Cr⁶⁺,Cr³⁺复合处理对狐尾藻的毒害作用较单一Cr⁶⁺,Cr³⁺显著,二者表现出协同作用,而其中Cr⁶⁺毒性大于Cr³⁺。     

Prostanoid formation in primary astroglial cell cultures: Ca-dependency and stimulation by A 23187, melittin and phospholipases A2 and C

Prostaglandin (PG) and thromboxane B₂ (TXB₂) biosynthesis was studied in cultured astrocytes from neonatal rat brain hemispheres. After two weeks of cultivation, prostanoids were formed with the spectrum: PGD₂ > TXB₂ > PGF₂ > PGE₂, as measured by specific radioimmunoassays. Under basal conditions PGD₂ biosynthesis (9.55 ng/mg protein/15 min) was in the same order of magnitude as the sum of the other prostanoids. The formation of prostanoids was stimulated in a concentration dependent manner (up to 6–10 fold) by the calcium ionophore A 23187 (0.01–10 μM) as well as by melittin (0.01–5 μg/ml), phospholipase A₂ (10–40 U/ml) and phospholipase C (0.01–1 U/ml). Basal and evoked PG and TXB₂ biosynthesis depended on the availability of Ca²⁺, as demonstrated in Ca²⁺ free incubation medium containing Na₂EDTA (1 μM), or with verapamil (100 μM) and 3,4,5-trimethoxybenzoic acid-8-(diethylamino)-octylester-HCl (TMB-8, 1–100 μM). Indomethacin (10 μM), mepacrine (100 μM) and p-bromophenacylbromide (50 μ M) inhibited basal and evoked PG formation. Thin-layer chromatography (TLC) detection after incubation of the cells with [³H]arachidonic acid (1 μCi/ml, for 60 min) confirmed the results obtained by radioimmunoassay. Incubation of [³H]arachidonic acid labelled cells with inonophore or phospholipases, followed by lipid extraction and TLC, showed that A 23187 liberated [³H]arachidonic acid predominantly from phosphatidylethanolamine, whereas phospholipase A₂ and C reduced mainly the labelling of the phosphatidyl-inositol/-choline fraction. Potassium depolarization of the cells did not enhance prostanoid formation. Similarly, drugs with affinity to - or β-adrenoceptors, or to dopamine-, 5-hydroxytryptamine-, muscarine-, histamine-, glutamate-, aspartate-, GABA, adenosine- and opioid-receptors failed to stimulate prostanoid biosynthesis. Also compounds like angiotensin, bradykinin and thrombin were ineffective in this respect.

In conclusion, our results confirm that cultured astrocytes possess the complete pattern of enzymes necessary for prostanoid formation and hence might play a crucial role in brain prostanoid biosynthesis. Stimulation of prostanoid biosynthesis involves Ca²⁺-dependent activation of phospholipase A₂, cyclooxygenase reaction and further PG metabolism. However, the endogenous stimulus for enhanced prostanoid synthesis in the brain still has to be established.     

Stimulation of platelet serotonin and Rb uptake by N-ethylmaleimide

The effects of N-ethylmaleimide (NEM) on mouse platelet serotonin (5-HT) and ⁸⁶Rb⁺ uptake were studied. The 5-HT transport system showed a biphasic response to increasing concentrations of NEM, with low concentrations (25–50 μM) stimulating and high concentrations (200–400 μM) inhibiting 5-HT transport. Fluoxetine, an inhibitor of the platelet 5-HT transporter, blocked NEM-induced stimulation of 5-HT transport. The kinetics of 5-HT uptake indicated that NEM (50 μM) markedly increased the maximal rate of 5-HT transport (V_max control = 28.4±1.4 pmol/10⁸ platelets/4 min vs V_max NEM = 64.5±9.5 pmol/10⁸ platelets/4 min but had no significant effect on the K_m value. Platelet Na⁺ K⁺ ATPase activity was determined by measuring ⁸⁶Rb⁺ uptake. Platelet ⁸⁶Rb⁺ uptake showed a biphasic response to NEM, with low concentrations (25–100 μM) significantly stimulating and high concentrations (400 μM) inhibiting uptake. These changes in platelet ⁸⁶Rb⁺ uptake paralleled the biphasic changes in 5-HT transport. In the presence of fluoxetine, 5-HT transport was markedly inhibited but no change in the ability of NEM to stimulate ⁸⁶Rb⁺ uptake was observed. These data suggest that low concentrations of NEM activate plasma membrane Na⁺ K⁺ ATPase which results in a marked stimulation of platelet 5-HT transport.     

Critical review of the methods used to measure the apparent dissociation constant and ligand purity in Ca2+ and Mg2+ buffer solutions

Using simulated Ca²⁺ and Mg²⁺ buffers, methods proposed to measure both ligand purity and the apparent dissociation constant (K_app) were investigated regarding (1) predicted accuracy of both parameters and (2) generality of the solution.

The Bers’ Ca²⁺ macroelectrode method [Bers, D. M., 1982 A simple method for the determination of free [Ca] in Ca-EGTA solutions Am. J. Physiol. 242, C404–C408] cannot be used with Mg²⁺-macroelectrodes and is partly arbitrary since the linear part of the Scatchard plot is judged subjectively. Iterative methods have therefore been introduced. Iteration based on the Bers’ method or the lumped interference in the Nicolsky–Eisenman equation also failed with Mg²⁺ macroelectrodes. The Oiki et al., method [Oiki, S., Yomamoto, T., Okada, Y., 1994. Apparent stability constants and purity of Ca-chelating agents evaluated using Ca-sensitive electrodes by the double-log optimization method Cell Calcium 15, 209–46.] cannot be applied to Mg²⁺ macroelectrodes. The pH titration method of Moisescu and Pusch (Pflügers, Arch., 355, R122, 1975) predicted EGTA purity and Ca²⁺ contamination, but K_app values for EGTA were approximate. It cannot be applied to Mg²⁺ binding. The partition method [Godt, R.E., 1974. Calcium-activated tension of skinned muscle fibres of the frog. Dependence on magnesium adenosine triphosphate concentration J. Gen. Physiol. 63, 722–739.] only approximately estimated the K_app. Calibration, maintaining contaminating [Ca²⁺]/[Mg²⁺] at <1 μmol l⁻¹, and setting standards by dilution, is the ultimate check of calculated ionised concentrations, although technically difficult. The macroelectrode method of Lüthi et al. [1997. Calibration of Mg²⁺-selective macromolecules down to 1 μmol l⁻¹ in intracellular and Ca⁺- containing extracellular solutions. Exp. Physiol. 82, 453–467] accurately predicted purity and K_app at pK_app values >4 and was independent of electrode characteristics. It is considered the method of choice.

Macroelectrode primary calibration should be carried out in solutions varying from 0.5 to 10 mmol l⁻¹ combined with either Ca–EGTA or Mg–EDTA buffers; the [Ca²⁺] and [Mg²⁺] in other buffer ligands can be measured in a secondary calibration.     

Nuclear maturation of ovine oocytes in cultured preantral follicles

Small (150–250 μm in diameter) and large (251–400 μm in diameter) preantral follicles (PFs) in sheep were cultured for 6 days in four different concentrations of transforming growth factor-alpha (TGF-), epidermal growth factor (EGF), FSH and LH. Proportions of follicles exhibiting growth, antrum formation and increase in follicular and oocyte diameter were the initial indicators of development. The ability of the oocytes isolated from these cultured follicles to mature to metaphase II (MII), after 24 h culture in a known in vitro maturation medium was the final criterion of success. TGF- 2.5 ng ml⁻¹, EGF 50 ng ml⁻¹ and FSH 1 and 2 μg ml⁻¹ supported good initial growth of the PFs. Thirty and seventeen percent of the oocytes from the large PFs cultured in TGF- 2.5 ng ml⁻¹ and FSH 2 μg ml⁻¹ respectively, matured to the MII stage. These proportions for oocytes from small PFs were 11 and 6%, respectively. Oocytes from follicles cultured in EGF did not mature to the MII stage. LH at all concentrations tested and TGF-, EGF and FSH above 5, 50 ng ml⁻¹ and 2 μg ml⁻¹, respectively, induced degeneration of the PFs. It was concluded that (i) TGF- 2.5 ng ml⁻¹ supports development of large PFs in sheep to obtain meiotically competent oocytes, (ii) PFs > 250 μm in initial diameter develop better in vitro, and (iii) in vitro development of sheep PFs could be obtained independent of gonadotropin stimulation.     

Bacterial resistance and detoxification of heavy metals

Microbial cells have resistances to essentially all of the toxic heavy metals of the Periodic Table. In bacterial cells, the genetic determinants of these resistances are frequently found on small extrachromosomal plasmids and transposons. Sometimes the resistances are associated with detoxifying enzymes. This is true for the Hg²⁺ → Hg⁰ reductase, the As³⁺ → As⁵⁺ oxidase and the Cr⁶⁺ → Cr³⁺ reductase. In other cases, such as As⁵⁺, Ag⁺ and Cd²⁺, no change in redox state occurs but, rather, uptake and transport differences accompany resistance determinants. This article summarizes what is known of bacterial metal resistances for which enzymatic detoxification is known to be the mechanism of resistance. The characteristics and functions of the enzymes are described, as well as a summary of the newer DNA sequence analysis (basic science) and bench-scale efforts (applied science) for the mercuric resistance system.     

Mg2+ ion effect on conformational equilibrium of poly A . 2 poly U and poly A poly U in aqueous solutions

Differential UV spectroscopy and thermal denaturation were used to study the Mg²⁺ ion effect on the conformational equilibrium in poly A · 2 poly U (A2U) and poly A · poly U (AU) solutions at low (0.01 M Na⁺) and high (0.1 M Na⁺) ionic strengths. Four complete phase diagrams were obtained for Mg²⁺–polynucleotide complexes in ranges of temperatures 20–96 °C and concentrations (10⁻⁵–10⁻²) M Mg²⁺. Three of them have a ‘critical’ point at which the type of the conformational transition changes. The value of the ‘critical’ concentration ([Mg_t²⁺]_cr=(4.5±1.0)×10⁻⁵ M) is nearly independent of the initial conformation of polynucleotides (AU, A2U) and of Na⁺ contents in the solution. Such a value is observed for Ni²⁺ ions too. The phase diagram of the (A2U+Mg²⁺) complex with 0.01 M Na⁺ has no ‘critical’ point: temperatures of (3→2) and (2→1) transitions increase in the whole Mg²⁺ range. In (AU+Mg²⁺) phase diagram at 0.01 M Na⁺ the temperature interval in which triple helices are formed and destroyed is several times larger than at 0.1 M Na⁺. Using the ligand theory, a qualitative thermodynamic analysis of the phase diagrams was performed.     

Simple and rapid determination of irinotecan and its metabolite SN-38 in plasma by high-performance liquid-chromatography: application to clinical pharmacokinetic studies

Irinotecan (CPT-11) is an anticancer agent widely employed in the treatment of colorectal carcinoma. A simple, rapid and sensitive high-performance liquid chromatographic method for the simultaneous determination of CPT-11 and its metabolite SN-38 in plasma, and their preliminary clinical pharmacokinetics are described. Both deproteinisation of plasma specimens (100 μl) and addition of the internal standard, camptothecin (CPT), are achieved by incorporating to samples 100 μl of a solution of CPT (1 μg/ml) in acetonitrile–1 mM orthophosphoric acid (90:10); 200 μl of this acidified acetonitrile solution, drug-free, is also added to accomplish complete deproteinisation: this procedure reduces sample preparation time to a minimum. After deproteinisation, samples are treated with potassium dihydrogenphosphate (0.1 M) and injected into a Nucleosil C₁₈ (5 μm, 250×4.0 mm) column. Mobile phase consists of potassium dihydrogenphosphate (0.1 M)–acetonitrile (67:33), at a flow-rate of 1 ml/min. CPT-11, SN-38 and CPT are detected by fluorescence with excitation wavelength set at 228 nm and emission wavelengths of CPT-11, SN-38 and CPT fixed, respectively, at 450, 543 and 433 nm. The limits of quantitation for CPT-11 and SN-38 are 1.0 and 0.5 ng/ml, respectively. This method shows good precision: the within day relative standard deviation (RSD) for CPT-11 (1–10 000 ng/ml) is 5.17% (range 2.15–8.27%) and for SN-38 (0.5–400 ng/ml) is 4.33% (1.32–7.78%); the between-day RSDs for CPT-11 and SN-38, in the previously described ranges, are 6.82% (5.03–10.8%) and 4.94% (2.09–9.30%), respectively. Using this assay, plasma pharmacokinetics of CPT-11, SN-38 and its glucuronidated form, SN-38G, have been determined in one patient receiving 200 mg/m² of CPT-11 as a 90 min intravenous infusion. The peak plasma concentration of CPT-11 at the end of the infusion is 3800 ng/ml. Plasma decay is biphasic with a terminal half-life of 11.6 h. The volume of distribution at steady state (V_ss) is 203 l/m², and the total body clearance (Cl) is 14.8 l/h·m². The maximum concentrations of SN-38 and SN-38G reach 28.9 and 151 ng/ml, respectively.     

The use of chemically modified and unmodified cassava waste for the removal of Cd, Cu and Zn ions from aqueous solution

The use of different chemically modified cassava waste biomass for the enhancement of the adsorption of three metal ions Cd, Cu and Zn from aqueous solution is reported in this paper. Treating with different concentrations of thioglycollic acid modified the cassava waste biomass.

The sorption rates of the three metals were 0.2303 min⁻¹ (Cd²⁺), 0.0051 min⁻¹ (Cu²⁺), 0.0040 min⁻¹ (Zn²⁺) and 0.109 min⁻¹ (Cd²⁺), 0.0069 min⁻¹ (Cu²⁺), 0.0367 min⁻¹ (Zn²⁺) for 0.5 and 1.00 M chemically modified levels, respectively. The adsorption rates were quite rapid and within 20–30 min of mixing, about 60–80% of these ions were removed from the solutions by the biomass and that chemically modifying the binding groups in the biomass enhanced its adsorption capacity towards the three metals. The results further showed that increased concentration of modifying reagent led to increased incorporation, or availability of more binding groups, in the biomass matrix, resulting in improved adsorptivity of the cassava waste biomass. The binding capacity study showed that the cassava waste, which is a serious environmental nuisance, due to foul odour released during decomposition, has the ability to adsorb trace metals from solutions.     

Cyclic ADP-ribose induced Ca release in rabbit skeletal muscle sarcoplasmic reticulum

The Ca²⁺-mobilizing metabolite cyclic ADP-ribose (cADPR) has been shown to release Ca²⁺ from ryanodine-sensitive stores in many cells. We show that this metabolite at a concentration of 17μM, but not its precursor β-NAD⁺ nor non-cyclic ADPR at the same concentration, is active in releasing Ca²⁺ from rabbit skeletal muscle sarcoplasmic reticulum. The release was not sensitive to Ruthenium red (1μM) nor to the ryanodine receptor-specific scorpion toxin Buthotus₁-1 (10 μM). In planar bilayer single channel recordings, concentrations up to 50μM cADPR did not increase the open probability of Ruthenium red and toxin-sensitive Ca²⁺ release channels. Thus Ca²⁺ release induced by cADPR in skeletal muscle sarcoplasmic reticulum may not involve opening of ryanodine receptors.     

Dopamine receptors in human foetal brains: Characterization, regulation and ontogeny of [H]spiperone binding sites in striatum

Eighteen corpora striata from normal human foetal brains ranging in gestational age from 16 to 40 weeks and five from post natal brains ranging from 23 days to 42 years were analysed for the ontogeny of dopamine receptors using [³H]spiperone as the ligand and 10 mM dopamine hydrochloride was used in blanks. Spiperone binding sites were characterized in a 40-week-old foetal brain to be dopamine receptors by the following criteria: (1) It was localized in a crude mitochondrial pellet that included synaptosomes; (2) binding was saturable at 0.8 nM concentration; (3) dopaminergic antagonists spiperone, haloperidol, pimozide, trifluperazine and chlorpromazine competed for the binding with IC₅₀ values in the range of 0.3–14 nM while agonists—apomorphine and dopamine gave IC₅₀ values of 2.5 and 10 μM, respectively suggesting a D₂ type receptor.

Epinephrine and norepinephrine inhibited the binding much less efficiently while mianserin at 10 μM and serotonin at 1 mM concentration did not inhibit the binding. Bimolecular association and dissociation rate constants for the reversible binding were 5.7 × 10⁸ M⁻¹ min⁻¹ and 5.0 × 10⁻² min⁻¹, respectively. Equilibrium dissociation constant was 87 pM and the K_D obtained by saturation binding was 73 pM.

During the foetal age 16 to 40 weeks, the receptor concentration remained in the range of 38–60 fmol/mg protein or 570–1080 fmol/g striatum but it increased two-fold postnatally reaching a maximum at 5 years Significantly, at lower foetal ages (16–24 weeks) the [³H]spiperone binding sites exhibited a heterogeneity with a high (K_D, 13–85 pM) and a low (K_D, 1.2–4.6 nM) affinity component, the former accounting for 13–24% of the total binding sites. This heterogeneity persisted even when sulpiride was used as a displacer. The number of high affinity sites increased from 16 weeks to 24 weeks and after 28 weeks of gestation, all the binding sites showed only a single high affinity.

GTP decreased the agonist affinity as observed by dopamine competition of [³H]spiperone binding in 20-week-old foetal striata and at all subsequent ages. GTP increased IC₅₀ values of dopamine 2 to 4.5 fold and Hill coefficients were also increased becoming closer to one suggesting that the dopamine receptor was susceptible to regulation from foetal life onwards.     

Studies on the interaction between Cd(2+) ions and DNA

Cadmium is a potent carcinogen in rodents and has recently been accepted by the International Agency for Research on Cancer as a category 1 (human) carcinogen, but the molecular mechanism of its action remains largely unclear. It has however been suggested that cadmium-induced carcinogenesis may involve either direct or indirect interaction of Cd²⁺ with DNA. Cd²⁺ is believed to bind covalently with N7 centres of adenine and guanine. At low concentrations (≤50 mM), Cd²⁺ is found to react with plasmid DNA to produce a mixture of Form I and Form II bands whereas at higher concentrations (≥100 mM), Cd²⁺ causes extensive damage to DNA at a pH 5.8 solution of cadmium nitrate. Within the range 0–100 mM (when pH is adjusted to 7.4 by adding NaOH) an increase in concentration of Cd²⁺ is found to cause a decrease in the gel mobility rate of plasmid and an increase in the intensity of the Form II band. When plasmid DNA is digested with BamH1, only the Form III band is observed both in the presence and absence of Cd²⁺. However, the mobility of the band is found to decrease with the increase in the concentration of Cd²⁺. When the enzyme Ssp1 which cuts plasmid DNA at the AT sites is used instead of BamH1, two bands are observed in the presence of cadmium as against one band in the absence of cadmium. These results suggest that Cd²⁺ binds covalently with DNA (possibly at G, A and T centres) and can form intrastrand bifunctional AT adducts but not the GG adducts. It may also be that neither GG nor AT adducts are formed and yet Ssp1 digestion is prevented because of a structural modification introduced in adenine by its interaction with Cd²⁺. In the presence of antioxidants such as cysteine, glutathione and ascorbate (especially cysteine and ascorbate), DNA damage is found to be greater than expected for the combined effects of the antioxidant and Cd²⁺. The increased DNA damage is believed to be due to the formation of reactive oxygen species (ROS).     

Response time and electrorheology of semidiluted gellan, xanthan and cellulose suspensions

Response times with electrical fields of gellan and xanthan dry powder suspensions of 25, 32 and 53 μm average diameter and concentrations of 1.0, 1.5 and 2.0% (w/w) dispersed in commercial corn oil were optically measured through a specifically designed set up. In all cases, the delay time was proportional to 1/E^a, where E is the applied field and a is an adjustable parameter. The values of parameter a were very different from the typical value of some known electrorheolgical fluids. Response time of gellan suspensions was shorter than the one obtained for xanthan and it is comparable to the time found by using silica particles in silicon oil. Response times for cellulose were very large and the fibrillation phenomenon was negligible for E<1.0 kv/mm.

Viscosity measurements of semidiluted xanthan, gellan and cellulose suspensions (1.0 and 1.5% w/w) under the influence of electrical fields, were performed in a parallel plates rheometer. Results in the range of stress <70 Pa showed that viscosity values of gellan suspensions were larger than those obtained with xanthan or cellulose under the same applied electric field at shear rates higher than 10 s⁻¹. However, cellulose suspensions showed larger viscosity values compared with the ones measured with xanthan and gellan suspensions at very low shear rates. Dielectric measurements of cellulose, xanthan and gellan 1.5% w/w suspensions were performed in the range 10⁰–8×10⁴ Hz. Results agree with a Maxwell–Wagner type relaxation model.     

Screening for synergistic interactions in dilute polysaccharide solutions

A simple viscometric approach has been used to screen for binding interactions between different polysaccharides in very dilute solution where exclusion effects should be negligible. The method involves preparing stock solutions to approximately the same, low, viscosity (η_sp≈1), dialysing to identical ionic conditions, mixing in various proportions, and looking for departures from the initial common viscosity.

Mixtures of xanthan or de-acetylated xanthan with locust bean gum (LBG) or konjac glucomannan (KM) show massive enhancement of viscosity, as anticipated from the formation of synergistic gels at higher concentrations. However, no viscosity changes on mixing with LBG or KM were observed for other conformationally ordered bacterial polysaccharides (welan and rhamsan) or for alginate and pectin with sufficient Ca²⁺ to induce almost complete conversion to the dimeric ‘egg box’ form, demonstrating that conformational rigidity is not, in itself, sufficient for other polysaccharides to form heterotypic junctions with mannan or glucomannan chains.

Interactions of carrageenans with LBG appear to depend on both conformation and the extent of aggregation. Mixtures of LBG with K⁺ kappa carrageenan in 100mM KCl (which is known to promote extensive aggregation of double helices) gave erratic values for rotational viscosity and showed typical gel-like mechanical spectra under low-amplitude oscillation. Disordered carrageenans (K⁺ kappa in water and lambda in 100mM KCl) showed no evidence of interaction with LBG. Negative results were also obtained for iota carrageenan under ionic conditions believed to promote ordering without significant aggregation (100mM KCl). However, under conditions where limited aggregation might be expected (iota carrageenan in 90 mM CaCl₂; Me₄N⁺ kappa carrageenan in 150 mM Me₄NI), significant reductions in viscosity were observed on mixing with LBG, which may indicate some intermolecular association but without the formation of an extended network structure.     

Effects of group I cations on the gelation of iota carrageenan

N.m.r. and rheological measurements have been used to study the gelation of iota carrageenan. Gelation has been found to occur only at polymer concentrations above the critical entanglement concentration. The high temperature sol state above the gel-sol transition appears to be an entangled polymer network. Although Li⁺ and Na⁺ ions are less effective at gelling the polymer than K⁺, Rb⁺ and Cs⁺ all cationic forms studied gel at sufficiently high polymer concentration and ionic strength. ⁷Li⁺, ²³Na, ³⁹K, ⁸⁷Rb and ¹³³Cs n.m.r. studies have been made as a function of temperature. The lithium salt form (2.2% w/w concentration) formed a viscoelastic solution at room temperature. The other salt forms gelled on cooling. The spectra of Li, Na and Cs carrageenan showed little change on heating whereas K and Rb spectra showed marked changes in apparent intensity. The nature of the cation interaction with the juntion zones is discussed.     

Influence of sucrose on the rheology and granule size of cross-linked waxy maize starch dispersions heated at two temperatures

Cross-linked waxy maize (CWM) starch dispersions (STDs) of concentration 50 g kg⁻¹ were heated in sucrose solutions containing 0–600 g kg⁻¹ (g sucrose/kg dispersion) at 85 °C at low shear and in intermittently agitated cans at 110 °C. The STDs heated in 0–300 g kg⁻¹ sucrose exhibited antithixotropic behavior, while those heated in 400–600 g kg⁻¹ sucrose exhibited thixotropic behavior. The mean starch granule diameter of the starch dispersions did not show strong dependence on sucrose concentration. The dispersions, especially those with high sucrose concentrations and heated at 110 °C, exhibited G′ versus frequency (ω) profiles of gels. The STDs exhibited first normal stress differences that increased in magnitude with the concentration of sucrose. Values of the first normal stress coefficient of canned dispersions calculated from dynamic rheological data plotted against ω and experimental values plotted against shear rate of some of the STDs overlapped.     

Nutrient removal by thermophilic Fischerella (Mastigocladus laminosus) in a simulated algaculture process

A novel nutrient removal/waste heat utilization process was simulated using semicontinuous cultures of the thermophilic cyanobacterium Fischerella. Dissolved inorganic carbon (DIC)-enriched cultures, maintained with 10 mg l⁻¹ daily productivity, diurnally varying temperature (from 55°C to 26–28°C), a 12:12 light cycle (200 μE sec⁻¹ m⁻²) and 50% biomass recycling into heated effluent at the beginning of each light period, removed > 95% of NO₃⁻ + NO₂⁻−N, 71% of NH₃-N, 82% of PO₄³⁻ −P, and 70% of total P from effluent water samples containing approximately 400 μg l⁻¹ combined N and 60 μg l⁻¹ P. Nutrient removal was not severely impaired by an altered temperature gradient, doubled light intensity, or DIC limitation. Recycling 75% of the biomass at the end of each light period resulted in unimpaired NO₃⁻ + NO₂⁻ removal, 38–45% P removal and no net NH₃ removal. Diurnally varying P removal, averaging 50–60%, and nearly constant > 80% N removal, are therefore projected for a full-scale process with continuous biomass recycling.     

Inhibition of Bradykinin-Induced Phosphoinositide Hydrolysis and Ca Mobilisation by Phorbol Ester in Rat Cultured Vascular Smooth Muscle Cells

Regulation of the increase in inositol phosphate (IP) production and intracellular Ca²⁺ concentration ([Ca²⁺]_i by protein kinase C (PKC) was investigated in cultured rat vascular smooth muscle cells (VSMCs). Pretreatment of VSMCs with phorbol 12-myristate 14-acetate (PMA, 1 μM) for 30 min almost abolished the BK-induced IP formation and Ca²⁺ mobilisation. This inhibition was reduced after incubating the cells with PMA for 4 h, and within 24 h the BK-induced responses were greater than those of control cells. The concentrations of PMA giving a half-maximal (pEC₅₀) and maximal inhibition of BK induced an increase in [Ca²⁺]_i, were 7.8 ± 0.3 M and 1 μM, n = 8, respectively. Prior treatment of VSMCs with staurosporine (1 μM), a PKC inhibitor, inhibited the ability of PMA to attenuate BK-induced responses, suggesting that the inhibitory effect of PMA is mediated through the activation of PKC. Paralleling the effect of PMA on the BK-induced IP formation and Ca²⁺ mobilisation, the translocation and downregulation of PKC isozymes were determined by Western blotting with antibodies against different PKC isozymes. The results revealed that treatment of the cells with PMA for various times, translocation of PKC-, βI, βII, δ, ε, and ζ isozymes from the cytosol to the membrane were seen after 5 min, 30 min, 2 h, and 4 h of treatment. However, 24-h treatment caused a partial downregulation of these PKC isozymes in both fractions. Treatment of VSMCs with 1 μM PMA for either 1 or 24 h did not significantly change the K_D and B_max of the BK receptor for binding (control: K_D = 1.7 ± 0.2 nM; B_max = 47.3 ± 4.4 fmol/mg protein), indicating that BK receptors are not a site for the inhibitory effect of PMA on BK-induced responses. In conclusion, these resuts demonstrate that translocation of PKC-, βI, βII, δ, ε, and ζ induced by PMA caused an attenuation of BK-induced IPs accumulation and Ca²⁺ mobilisation in VSMCs.