The respiratory inhibitor antimycin A specifically binds Fe(III) ions and mediates utilization of iron by the halotolerant alga Dunaliella salina (Chlorophyta)

It is demonstrated that Antimycin A (AA), a respiratory inhibitor produced by Streptomyces bacteria, forms lipophylic complexes with Fe(III) ions. Spectroscopic titration indicates that Fe(III) ions interact with 2AA molecules. At growth-limiting Fe concentrations, AA mediates Fe uptake and promotes growth and chlorophyll synthesis better than other Fe chelators in the halotolerant alga Dunaliella salina. It is proposed that AA enhances Fe bioavailability in hypersaline solutions by formation of lipophylic Fe-AA complexes which are taken-up and utilized by the algae. The results suggest that the respiratory inhibitor AA can affect Fe metabolism in microorganisms.     

Method for isolating single cardiac cells in the guinea pig using pronase. The role of calcium ions

A method for isolation of guinea-pig cardiomyocytes with pronase has been developed. The method has been assessed in hearts perfused with solutions containing pronase (1 U/ml) and 200 microM Ca2+. Eighty per cent of the cells released were rod-shaped and 1.2 mM Ca2+ tolerant. Enriched medium 199 was used for all solutions. Sodium and slow inward currents recorded from cells dispersed with pronase were similar to those recorded from cells isolated after prolonged exposure to collagenase. Two principal factors are to be marked: (a) presence of high enough amounts of Ca2+ in enzyme solution (up to 200 microM); (b) use of the enriched medium in all the stages of the procedure.     

Bulb mite,Rhizoglyphus robini (Astigmata: Acaridae) as an experimental animal

Rhizoglyphus robini Claparède (Acari: Astigmata: Acaridae) is proposed as a model laboratory animal for biological, ecological, physiological and toxicological studies. The mite is easy and inexpensive to rear, quite fecund, convenient to manipulate, and may rapidly be raised to gram quantities. Examples are presented of its use in soil pest ecology and control studies, and in physiological, biochemical and toxicological investigations. Efforts to explore the induction of detoxification systems by various chemicals, and a demonstration of its control by solarization, are also described.     

Refractive index and thickness of the outer layer of particles of dispersed perfluorochemical-based blood substitutes

A calculation of the refractive index of particles of a disperse perfluorochemical-based (PFC-based) blood substitute has been made taking into account particular features of the structure of PFC emulsion particles and the equations earlier obtained by one of the authors in the studies on light interaction with optically inhomogeneous 2- and 3-layer spheres. The possibility of averaging by volume the refractive index of 2-layer emulsion particles has been shown. The refractive index of PFC particles has been experimentally determined using independent optical methods, and the thickness of the particle shell formed by a surfactant has been evaluated.     

ATP-induced ΔpH formation in chloroplast ATP synthase proteoliposomes

Summary A procedure to reconstitute CF₀CF₁ proteoliposomes by gel filtration through a Sephadex-column pre-equilibrated with valinomycin and potassium is described. Proteoliposomes reconstituted by this procedure catalyze an ATP-induced pH of 2.5 to 3.5 units. pH was measured with either 9-aminoacridine or with the pH indicator pyranine trapped inside the proteoliposomes. CF₀CF₁ proteoliposomes prepared by conventional techniques catalyzed an ATP-induced formation, but were unable to catalyze an ATP-induced pH even in the presence of valinomycin.The ATP-induced pH was sensitive to uncouplers and energy transfer inhibitors and was increased at low temperatures. It is suggested that ATP-induced pH was observed in these proteoliposomes due to the efficient removal of intravesicular ammonium introduced with the CF₀CF₁ preparation. The ammonium acted as an internal buffer, and thus prevented an observable pH formation.     

Salt-induced cooperativity in ATPase activity of plasma membrane-enriched fractions from cultured Citrus cells: kinetic evidence

ATPase activity was studied in plasma membrane-enriched fractions prepared from cultured Citrus sinensis L. cv. Osbeck cells. In general, properties of the plasma membrane ATPase from cultured cells, such as optimal pH and temperature. V_max and K_m were similar to those already observed in higher plants. The effects of high salt concentrations on ATPase activity were studied in membrane fractions derived from salt-sensitive and salt-tolerant cells grown in the presence or absence of salt. NaCl did not have an in vivo effect on V_max and the apparent K_m value for ATP. However, high concentrations of NaCl, or KCl, added in vitro, induced cooperativity in the enzyme and reduced the affinity of the enzyme for its substrate. Isoosmolar concentrations of sucrose or choline chloride failed to do so. Our results suggest that the plasma membrane ATPase of Citrus cells has more than one substrate-binding site on the native form of the enzyme which interact in the presence of salt and act independently in its absence.     

[K+] dependence of open-channel conductance in cloned inward rectifier potassium channels (IRK1, Kir2.1).

Potassium conduction through unblocked inwardly rectifying (IRK1, Kir2.1) potassium channels was measured in inside-out-patches from Xenopus oocytes, after removal of polyamine-induced strong inward rectification. Unblocked IRK1 channel current-voltage (I-V) relations show very mild inward rectification in symmetrical solutions, are linearized in nonsymmetrical solutions that bring the K+ reversal potential to extreme negative values, and follow Goldman-Hodgkin-Katz constant field equation at extreme positive E alpha. When intracellular K+ concentration (KIN) was varied, at constant extracellular K+ concentration (KOUT) the conductance at the reversal potential (GREV) followed closely the predictions of the Goldman-Hodgkin-Katz constant field equation at low concentrations and saturated sharply at concentrations of > 150 mM. Similarly, when KOUT was varied, at constant KIN, GREV saturated at concentrations of > 150 mM. A square-root dependence of conductance on KOUT is a well-known property of inward rectifier potassium channels and is a property of the open channel. A nonsymmetrical two-site three-barrier model can qualitatively explain both the I-V relations and the [K+] dependence of conductance of open IRK1 (Kir2.1) channels.