Effect of thyrotropin on glycosaminoglycans synthesized by primocultured thyroid cells

The synthesis of glycosaminoglycans (GAGs) was investigated in porcine thyroid cells under the influence or not of thyrotropin. After labelling with [³H] glucosamine and [³⁵S] $\text{SO}{}_4{}^{\mathrm{2?}}$, enriched GAG-fractions prepared from culture media, cells, and eventually substrate adhering materials, were analyzed by cellulose acetate electrophoresis combined with specific degradations. They comprised heparan sulfate and hyaluronic acid together with an unknown sulfated component labile to endo-β-galactosidase. Whereas global labellings of newly made GAGs were not significantly modified by thyrotropin, we reproducibly observed with the hormone a substantial increase in the proportion of hyaluronic acid [³H] label and, when cells organized into follicles, of the proportion of cell-associated [³H] GAGs. This system thus offers an interesting model to study how the responsiveness to an hormone and the reorganization that follows might implicate specific glycoconjugates.     

A 1H-NMR longitudinal relaxation study of the interaction between cytochrome c and cytochrome c oxidase

The interaction between the oxidized forms of cytochrome c and cytochrome c oxidase (EC 1.9.3.1) has been investigated by ¹H-NMR longitudinal relaxation measurements. It is found that relaxation of methyl groups on the heme ring of cytochrome c markedly deviates from a simple exponential behavior in the presence of small amounts of cytochrome oxidase. A comparison with the relaxation behavior of cytochrome c modified by 4-carboxy-3,5-dinitrophenyl at Lys-13 shows that the oxidase induces a conformation in native cytochrome c that is closely related to that of the derivative. It is suggested that this change in conformation consists of a rupture of the salt bridge between Lys-13 and Glu-90 and a concomitant perturbation of the methionine ligand.     

Physiological changes in, and phosphate uptake by potato plants during development of, and recovery from phosphate deficiency

The development of phosphate deficiency (P-stress) was observed in rooted sprouts of Solanum tuberosum L. cv. Desiree growing in solutions without phosphate. Shoot growth was inhibited by P-stress within 3 to 5 days of terminating the phosphate supply, while significant effects on root growth were not recorded until 7 to 9 days. Thus, the shoot:root dry weight ratio decreased from 4.3 to 2.6 over a 10-day period. Growth in the absence of an exogenous phosphate supply progressively diluted the phosphorus in the plant. The proportional decrease in concentration was similar in roots and shoots over a 7-day period, even though the former were growing more quickly. The potential for phosphate uptake per unit weight of root increased rapidly during the first 3 days of P-stress. When the plants were provided subsequently with a labelled, 1 mol m^?3 phosphate solution, the absorption rate was 3 to 4-fold greater than that of control plants which had received a continuous phosphate supply. The increased rate of uptake by P-stressed plants was accounted for by an increase (3-fold) in the V_max of system 1 for phosphate transport and by a marked increase in the affinity of the system for phosphate (decrease in K_m). In the early stages of P-stress, before marked changes in growth were measured, the proportion of labelled phosphate translocated to the shoots increased slightly relative to the controls when a phosphate supply was restored. In the later stages of stress a greater proportion was retained in the root system of P-stressed plants than in that of controls. In plants with roots divided between solutions containing or lacking a phosphate supply, the increased absorption rate was determined by the general demand for phosphate in the plant and not by the P-status of the particular root where uptake was measured. By contrast, the poportion translocated was strongly dependent on the P-status of the root. The restoration of a phosphate supply to P-stressed plants was marked by a rapid increase in the P concentration in snoots and roots which returned to levels similar to unstressed controls within 24 h. The enhanced uptake rate persisted for at least 5 days, resulting in supra-normal concentrations of P in both shoots and roots, and in the formation of extensive necrotic areas between the veins of mature leaves. Autoradiographs showed accumulations of ³²P in these lesions and at the points where guttation droplets formed on leaves.     

Toxic tetranortriterpenes of the fruit of Melia azedarach

Four new tetranortriterpenes, meliatoxins A₁, A₂, B₁ and B₂ have been isolated and identified as toxic constituents of the fruit of Melia azedarach L. var. australasica. Toxicity and pathological results confirm that the meliatoxins are responsible for most but not all of the symptoms resulting from the ingestion of whole fruit.     

Are allozymes differing in substrate specificity involved in the evolution of Silene species?

Summary The concerted action of two flavone-skeleton modifying genes, P and Me, and the alleles of three independently segregating loci g, gl and fg involved in flavone-glycosylation lead to the 33 different flavones so far identified in Silene. The alleles of the different loci involved in flavone-glycosylation control enzymes which differ in substrate specificity, a phenomenon not often described in higher organisms. The alleles of the different loci are variously distributed over the different species. The possible evolutionary implications of these distributions are discussed.     

Studies on the prolonged storage of Metarhizium anisopliae conidia: effect of growth substrate on conidial survival and virulence against mosquitoes

Metarhizium anisopliae was grown on six complex mycological media and on three types of rice at three moisture levels to determine the effect of growth substrate on conidial yield, viability, and virulence against mosquitoes immediately after spore maturation and after the storage of conidia at four different temperature-relative humidity (RH) combinations over a 1-year period. Conidial yields varied with the mycological media, but the viability and virulence of conidia against mosquitoes produced on all substrates were similar when spores were stored under the same conditions. The storage conditions were more critical to spore survival and virulence than the substrate upon which conidia were produced. The comparison of rice types for conidial production indicated that conidial yield, viability, and virulence to mosquitoes were more dependent upon the moisture level during growth and on the storage conditions that upon the rice used. The best storage conditions among those tested for the retention of both spore viability and virulence against mosquitoes were 19°C–97% RH and 4°C–0% RH.     

Dielectric Spectroscopy: a Rapid Method for the Determination of Solvent Biocompatibility During Biotransformations

Dielectric spectroscopy provides a convenient means of determining the degree of intactness of biological cells. 4-terminal dielectric measurements of suspensions of Saccharomyces cerevisiae at 0.4 MHz show that, as with all other biological cells, these organisms possess a substantial β-dispersion. The additional of octanol to such suspensions causes a rapid decrease in the electrical capacitance of the suspension, which parallels the cellular viability as determined by methylene blue staining. The kinetics of cell death are determined in part by the rate of dissolution of the organic solvent in the aqueous phase. The toxicity of several organic solvents to S. cerevisiae is studied using this technique, and is found to be dependent upon the polarity of the solvent. The present method provides a simple and rapid means for assessing the biocompatibility of solvents used in biotransformations.     

Role of Hydroxyl Radicals in Escherzchza Colz Killing Induced by Hydrogen Peroxide

Escherichia coli lethality by hydrogen peroxide is characterized by two modes of killing. In this paper we have found that hydroxyl radicals (OH -) generated by H₂O₂ and intracellular divalent iron are not involved in the induction of mode one lethality (i.e. cell killing produced by concentrations of H₂O₂ lower than 2.5 mM). In fact, the OH radical scavengers, thiourea, ethanol and dimethyl sulfoxide, and the iron chelator, desferrioxarnine, did not affect the survival of cells exposed to 2.5mM H₂O₂. In addition cell vulnerability to the same H₂O₂ concentration was independent on the intracellular iron content. In contrast, mode two lethality (i.e. cell killing generated by concentrations of H₂O₂ higher than 10mM) was markedly reduced by OH radical scavengers and desferrioxamine and was augmented by increasing the intracellular iron content.

It is concluded that OH. are required for mode two killing of E. coli by hydrogen peroxide.     

Chronotoxicity of Sodium Valproate and Its Mechanisms in Mice: Dose-Concentration-Response Relationship

A significant circadian rhythm of acute toxicity was demonstrated in mice with intraperitoneal (i.p.) injection of sodium valproate (VPA). The role of pharmacokinetics on the rhythms of the toxicity and electroshock seizure (ES) threshold was investigated. ICR male mice, housed under a light-dark (12 :12) cycle, were injected intraperitoneally 1200 mg/kg for the acute toxicity study and 300 mg/kg for the anticonvulsant effect study. In the acute toxicity, the highest mortality was found when VPA was injected at 1700 and the lowest at 0900 or 0100. The time course of mean plasma and brain VPA concentrations after an injection of VPA was not different between mice injected at 1700 and mice injected at 0100. In the anticonvulsant effect, no significant circadian rhythm was demonstrated for both the ES threshold and the plasma VPA concentrations after i.p. Injection, although a significant rhythm has been reported for them after oral administration. The results suggest that the circadian rhythm in the mortality after an i.p. Injection of VPA may be due to the rhythm in the sensitivity of the central nervous system to the drug and that the mechanism underlying the rhythm of VPA acute toxicity is different from that of the anticonvulsant action of VPA. The route and the time of drug administration are essentially important to study the anticonvulsant effect and acute toxicity of VPA in mice.     

Two substrate sites in the renal Na+-d-glucose cotransporter studied by model analysis of phlorizin binding and-d-glucose transport measurements

Summary Time courses of phlorizin binding to the outside of membrane vesicles from porcine renal outer cortex and outer medulla were measured and the obtained families of binding curves were fitted to different binding models. To fit the experimental data a model with two binding sites was required. Optimal fits were obtained if a ratio of low and high affinity phlorizin binding sites of 1:1 was assumed. Na⁺ increased the affinity of both binding sites. By an inside-negative membrane potential the affinity of the high affinity binding site (measured in the presence of 3 mM Na⁺) and of the low affinity binding site (measured in the presence of 3 or 90 mM Na⁺) was increased. Optimal fits were obtained when the rate constants of dissociation were not changed by the membrane potential. In the presence of 90 mM Na⁺ on both membrane sides and with a clamped membrane potential,K _D values of 0.4 and 7.9 M were calculated for the low and high affinity phlorizin binding sites which were observed in outer cortex and in outer medulla. Apparent low and high affinity transport sites were detected by measuring the substrate dependence ofd-glucose uptake in membrane vesicles from outer cortex and outer medulla which is stimulated by an initial gradient of 90 mM Na⁺(out>in). Low and high affinity transport could be fitted with identicalK _m values in outer cortex and outer medulla. An inside-negative membrane potential decreased the apparentK _m ofhigh affinity transport whereas the apparentK _m of low affinity transport was not changed. The data show that in outer cortex and outer medulla of pighigh and low affinity Na⁺-d-glucose cotransporters are present which containlow and high affinity phlorizin binding sites, respectively. It has to be elucidated from future experiments whether equal amounts of low and high affinity transporters are expressed in both kidney regions or whether the low and high affinity transporter are parts of the same glucose transport moleculc.