Mössbauer spectroscopy of iron-containing dermal granules from Molpadia intermedia

Dermal granules containing hydrous ferric oxide cores from Molpadia intermedia were studied by Mössbauer spectroscopy from 1.5 t0 300 K and in magnetic fields up to 80 kOersted at 4.2 K. A magnetic phase transition to an antiferromagnetically ordered state is observed at 10 K. The results are compared with the magnetic behavior of micellar cores of ferritin from eukaryotes and iron-storage materials from prokaryotes.     

Spontaneous opening at zero membrane potential of sodium channels from eel electroplax reconstituted into lipid vesicles

Summary The voltage-dependent sodium channel from the eel electroplax was purified and reconstituted into vesicles of varying lipid composition. Isotopic sodium uptake experiments were conducted with vesicles at zero membrane potential, using veratridine to activate channels and tetrodotoxin to block them. Under these conditions, channel-dependent uptake of isotopic sodium by the vesicles was observed, demonstrating that a certain fraction of the reconstituted protein was capable of mediating ion fluxes. In addition, vesicles untreated with veratridine showed significant background uptake of sodium; a considerable proportion of this flux was blocked by tetrodotoxin. Thus these measurements showed that a significant subpopulation of channels was present that could mediate ionic fluxes in the absence of activating toxins. The proportion of channels exhibiting this behavior was dependent on the lipid composition of the vesicles and the temperature at which the uptake was measured; furthermore, the effect of temperature was reversible. However, the phenomenon was not affected by the degree of purification of the protein used for reconstitution, and channels in resealed electroplax membrane fragments or reconstituted, solely into native eel lipids did not show this behavior. The kinetics of vesicular uptake through these spontaneously-opening channels was slow, and we attribute this behavior to a modification of sodium channel inactivation.     

Using Interorganizational Information Systems to Support Environmental Management Efforts at ASG

We examine use of environmental information systems by ASG AB (hereafter ASG), an international logistics and transport firm headquartered in Stockholm, Sweden, as a case study to illustrate the role of information systems in life-cycle-oriented environmental management. This case provides an example of how a firm can use interorganizational information systems (IOISs) to move toward environmentally sustainable business practices. Through the use of IOISs, ASG has been able to improve its environmental performance and that of its suppliers. Further, this improved environmental performance has been a competitive advantage for ASG and enabled it to attract new business. As such, ASG's experiences illustrate how aggressive practices move environmental management beyond compliance and cost control, at which many firms have been successful, to revenue generation. The case also shows how environmentally sustainable business practices can be integrated into a firm's strategy. In addition to illustrating how ASG has used IOISs to improve environmental performance, we compare their use of environmental ISs with the expected evolution of environmental ISs presented in the Shaft and colleagues (1997) framework. Although some of ASG's experiences verify the expected progression of these types of systems, some developments are not as expected. These differences have implications for the framework.     

Iron plaque enhances phosphorus uptake by rice (Oryza sativa) growing under varying phosphorus and iron concentrations

Both solution culture and pot experiments were performed to investigate (a) the effects of external Fe (II) concentrations and forms on the formation of iron plaque on the roots of rice (Oryza sativa) and subsequent P adsorption on iron plaque and shoot P concentrations and (b) the effects of soil moisture regimes on the formation of iron plaque and P adsorption on root surfaces and P accumulation in shoots. The results showed that iron plaque was significantly increased with increasing Fe²⁺ concentrations in the solution culture. The amounts of P adsorbed on the iron plaque were increased significantly with external Fe²⁺ concentrations. Although shoot P concentration was not significantly affected by Fe²⁺ treatment after incubation for 2 days, it was significantly increased in the Fe‐treated plants compared with Fe‐deprived ones after incubation for 4 days. Soil culture experiment showed that the formation of iron plaque on root surfaces was promoted by exogenous iron, with greater amount of iron plaque being formed by addition of ferric hydroxide than of ferric oxide. Phosphorus adsorption on iron plaque also increased with the addition of iron oxides, and increasing soil P increased the amounts of P associated with the iron plaque and shoot P concentration. The amounts of iron plaque were almost sixfold higher under flooding condition than under field capacity condition. Plants pretreated under flooding condition generally had higher shoot P concentrations when they were transplanted to solutions with varying P levels, and this was most pronounced in the treatment with highest solution P concentration. The results suggest that iron plaque acts as a nutrient reservoir for phosphorus in the rhizosphere and helps enhance P acquisition by rice.     

Ruthenium ammine complexes as electron acceptors for growth stimulation by plasma membrane electron transport

Ammineruthenium(III) complexes have been found to act as electron acceptors for the transplasmalemma electron transport system of animal cells. The active complexes hexaammineruthenium(III), pyridine pentaammineruthenium(III), and chloropentaammineruthenium(III) range in redox potential (E ₀) from 305 to –42 mV. These compounds also act as electron acceptors for the NADH dehydrogenase of isolated plasma membranes. Stimulation of HeLa cell growth, in the absence of calf serum, by these compounds provides evidence that growth stimulation by the transplasma membrane electron transport system is not entirely based on reduction and uptake of iron.     

Gramicidin A-phospholipid model systems

Gramicidin A forms ion-conducting channels which can traverse the hydrocarbon core of lipid bilayer membranes. The structures formed by gramicidin A are among the best characterized of all membrane-bound polypeptides or proteins. In this review a brief summary is given of the occurrence, conformation, and synthesis of gramicidin A, and of its use as a model for ion transport and the interaction of proteins and lipids in biological membranes.     

Regulation of the photosynthetic electron transport during dark-light transitions by activation of the ferredoxin-NADP+-oxidoreductase in higher plants

Absorbance changes associated with the oxidation and reduction of cytochrome f belong to the classical observations about the interaction of the two photosystems. A complex induction pattern of cytochrome f oxidation results, if both photosystems are excited simultaneously. This indicates a light-modulated regulation of the photosynthetic electron transport, which we examined for intact biological systems of decreasing complexity. The ferredoxin-NADP⁺-oxidoreductase (FNR) is suggested to be activated by light and inactivated in the dark. This is pointed out by the kinetics of variable fluorescence and by the influence of different artificial electron acceptors on the cytochrome f kinetics. The photoreduction of NADP⁺ by carefully prepared thylakoids demonstrates the activation process directly.This work was supported by the Deutsche Forschungsgemeinschaft.     

Implications for cytoplasmic pH,protonmotice force,and amino-acid transport across the plasmalemma of Riccia fluitans

By means of pH-sensitive microelectrodes, cytoplasmic pH has been monitored continuously during amino-acid transport across the plasmalemma of Riccia fluitans rhizoid cells under various experimental conditions. (i) Contrary to the general assumption that import of amino acids (or hexoses) together with protons should lead to cytoplasmic acidification, an alkalinization of 0.1–0.3 pH_c units was found for all amino acids tested. Similar alkalinizations were recorded in the presence of hexoses and methylamine. No alkalinization occurred when the substrates were added in the depolarized state or in the presence of cyanide, where the electrogenic H⁺-pump is inhibited. (ii) After acidification of the cytoplasm by means of various concentrations of acetic acid, amino-acid transport is massively altered, although the protonmotive force remained essentially constant. It is suggested that H⁺-cotransport is energetically interconnected with the proton-export pump which is stimulated by the amino-acid-induced depolarization, thus causing proton depletion of the cytoplasm. It is concluded that, in order to investigate H⁺-dependent cotransport processes, the cytoplasmic pH must be measured and be under continuous experimental control; secondly, neither pH nor the protonmotive force across a membrane are reliable quantities for analysing a proton-dependent process.Abbreviations 3-OMG 3-oxymethylglucose - pH_c cytoplasmic pH - _m electrical potential difference across the respective membrane, i.e. membrane potential - _H+/F (=pmf) electrochemical proton gradient     

Regulation of auxin transport in pea (Pisum sativum L.) by phenylacetic acid: effects on the components of transmembrane transport of indol-3yl-acetic acid

Phenylacetic acid (PAA), a naturally-occurring acidic plant growth substance, was readily taken up by pea (Pisum sativum L. cv. Alderman) stem segments from buffered external solutions by a pH-dependent, non-mediated diffusion. Net uptake from a 0.2 M solution at pH 4.5 proceeded at a constant rate for at least 60 min and, up to approx. 100 M, the rate of uptake was directly proportional to the external concentration of the compound. The net rate of uptake of PAA was not affected by the inclusion of indol-3yl-acetic acid (IAA) in the uptake medium (up to approx. 30 M) and, unlike the net uptake of IAA, was not stimulated by N-1-naphthylphthalamic acid (NPA) or 2,3,5-triiodobenzoic acid. At an external concentration of 0.2 M and pH 4.5, the net rate of uptake of PAA was about twice that of IAA. It was concluded that the uptake of PAA did not involve the participation of carriers and that PAA was not a transported substrate for the carriers involved in the uptake and polar transport of IAA. Nevertheless, the inclusion of 3–100 M unlabelled PAA in the external medium greatly stimulated the uptake by pea stem segments of [1-¹⁴C]IAA (external concentration 0.2 M). It was concluded that whilst PAA was not a transported substrate for the NPA-sensitive IAA efflux carrier, it interacted with this carrier to inhibit IAA efflux from cells. Over the concentration range 3–100 M, PAA progressively reduced the stimulatory effect of NPA on IAA uptake, indicating that PAA also inhibited carrier-mediated uptake of IAA. The consequences of these observations for the regulation of polar auxin transport are discussed.Abbreviations IAA indol-3yl-acetic acid - DMO 5,5-dimethyloxazolidine-2,4-dione - NPA N-1-naphthylphthalamic acid - PAA phenylacetic acid - TIBA 2,3,5-triiodobenzoic acid     

OmpR and EnvZ are pleiotropic regulatory proteins: positive regulation of the tripeptide permease (tppB) of Salmonella typhimurium

Summary The tppB locus of Salmonella typhimurium encodes the anaerobically-induced tripeptide permease. We have demonstrated that expression of tppB requires the function of the ompR and envZ gene products, originally identified as positive regulatory proteins required for the osmotic regulation of porin expression. Significantly, tppB expression is not osmotically regulated. We have also identified three additional genes whose expression depends on OmpR. Thus OmpR and EnvZ serve a more general regulatory role than has previously been supposed. This study provides the first detailed genetic analysis of the ompB locus of S. typhimurium.