Nigericin forms highly stable complexes with lithium and cesium

Nigericin is a monocarboxylic polyether molecule described as a mobile K⁺ ionophore unable to transport Li⁺ and Cs⁺ across natural or artificial membranes. This paper shows that the ion carrier molecule forms complexes of equivalent energy demands with Li⁺, Cs⁺, Na⁺, Rb⁺, and K⁺. This is in accordance with the similar values of the complex stability constants obtained from nigericin with the five alkali metal cations assayed. On the other hand, nigericinalkali metal cation binding isotherms show faster rates for Li⁺ and Cs⁺ than for Na⁺, K⁺, and Rb⁺, in conditions where the carboxylic proton does not dissociate. Furthermore, proton NMR spectra of nigericin-Li⁺ and nigericin-Cs⁺ complexes show wide broadenings, suggesting strong cation interaction with the ionophore; in contrast, the complexes with Na⁺, K⁺, and Rb⁺ show only clear-cut chemical shifts. These latter results support the view that nigericin forms highly stable complexes with Li⁺ and Cs⁺ and contribute to the explanation for the inability of this ionophore to transport the former cations in conditions where it catalyzes a fast transport of K⁺>Rb⁺>Na⁺.Part of the results of this paper were presented at the 14th International Congress of Biochemistry in Prague, Czechoslovakia.     

Ethanol tolerance and carbohydrate metabolism in lactobacilli

Summary This paper describes the ethanol tolerance and metabolism of 31 strains ofLactobacillus on glucose, xylose, lactose, cellobiose and starch. The purpose of this work was to determine the suitability of the 31 strains as potential host for the ethanol producing genes, pyruvate decarboxylase and aldehyde dehydrogenase, fromZymomonas mobilis. The 31 strains were screened for their ability to grow in 0 to 8% v/v ethanol on all five carbohydrates. Those strains that were able to grow to an OD of 1.0 in 8% ethanol were evaluated at ethanol concentrations up to 16%. v/v. The fermentative products from the five carbohydrates were analyzed to determine the ratios of lactic acid, ethanol, and acetic acid.Published as Paper No. 9786, Journal Series Nebraska Agricultural Experiment Station, Lincoln, NE 68583-0704.     

Proton-induced grana formation in chloroplasts. Distribution of chlorophyll-protein complexes and Photosystem II photochemistry

Lowering the pH of the incubation medium to pH 5.4 leads to grana formation morphologically similar to that induced by metal cations. The same phenomenon is observed in EDTA-washed chloroplasts, indicating that it is not due in part to electrostatic ‘masking’ by residual cations associated with the membranes. Digitonin fractionation studies have indicated that the distribution of the major chlorophyll-protein complexes between granal and stromal membrane regions is similar at pH 5.4 in the absence of Mg²⁺, and at pH 7.4 in the presence of Mg²⁺. Chlorophyll fluorescence induction studies have indicated that the primary photochemistry of Photosystem II (PS II) is stimulated by lowering the pH to 5.4, just as it is upon metal cation addition at higher pH values. The failure to observe such an increase at pH 5.4 by measuring electron transport to ferricyanide is attributed to a combination of an inhibition by this pH of electron transport at a site after Q reduction and an increase in the number of PS II centres detached from the plastoquinone pool. We conclude that the stacked configuration of chloroplast membranes leads to increased PS II primary photochemistry, which is most simply explained in terms of a redistribution of excitation energy towards PS II.     

Binding of nickel (II) to 5′-nucleoside monophosphates and related compounds

Summary The interactions of Ni(II) cation with a representative suite of purine bases and the respective nucleosides and nucleotides have been studied by ultraviolet difference spectroscopy. Apparent association constants, K_app, were determined for each system at pH 7.0, using computer linear regression coupled with an iteration technique. The specificity of binding of Ni²⁺ for the purine nucleotides studied at pH 7.0 was 5-GMP > 5-IMP > 5-AMP; a similiar ordering was also found for the respective nucleosides and bases. In this study binding was not observed for the suite of pyramidines used, although a Ni²⁺ - cytidine complex has been observed (Fiskin and Beer, 1965). It was also found that Ni²⁺ bound more strongly to the purine 5-nucleotides than to the respective nucleosides and bases. These trends are explained in terms of metal-ligand bonds and available bonding positions on the ligands. A role for metal-ion-nucleotide types of complexes is suggested in the processes that might have given rise to the origin of life.     

Development and pigmentation of chlorosomes in Chloroflexus aurantiacus strain Ok-70-fl

The development of chlorosomes and their pigmentation were studied by growing Chloroflexus aurantiacus strain Ok-7o-fl first under conditions under which BChl c-synthesis is low (50°C, 2000 lux and 30°C, 1500 lux) and subsequently under conditions promoting high BChl c-synthesis (50°C, 400 lux). Electron microscopic observations on and chemical analyses of isolated cell components showed that in BChl c-depleted cells chlorosome-like structures (chlorosome bags) are attached to fragments of cytoplasmic membranes. These chlorosome bags exhibit a periodic fine structure caused by the construction of the baseplates of the chlorosomes. The baseplates are closely attached to the cytoplasmic membrane, they are rich in phospholipids and apparently contain a 790 nm-BChl a-complex. Chlorosome bags of BChl c-depleted cells always contain a limited amount of light-harvesting pigment complexes (BChlc, - and -carotene). The light-harvesting system is restored (50°C, 400 lux) by first refilling the existing chlorosome bags before cell division takes place.Abbreviations BChl Bacteriochlorophyll - LH Light-harvesting complex - RC Reaction center     

Composition and function of human cervical mucus

Human cervical mucus was collected from seven donors during the follicular, ovulatory and luteal phases of the ovulatory menstrual cycle. Individual mucus samples were solubilized and fractionated on Sepharose columns into excluded mucins and low-molecular-weight proteins. Mucin fractions were highly purified, as evidenced by the presence of a single N-terminal amino acid residue, threonine, and by the absence of contaminating plasma proteins. Amino acid compositions of mucins isolated during different menstrual phases of a single donor or from different donors were similar. Mucin carbohydrate compositions were also similar, except for the sialic acid-to-fucose ratio, which varied significantly between donors but not within the menstrual cycle of a single donor. An analysis of variance was applied to evaluate the contribution of mucin composition to viscoelasticity, as quantitated by microrheometry. Viscoelasticity was dependent on the donor, on the percent nondialyzable solids and on the mucin content, but not on the phase of the menstrual cycle during which the sample was collected. These findings suggest that mucus function (viscoelasticity) is reflected in carbohydrate composition and/or structure and that this menstrual relationship is unique for each donor. Furthermore, the absence of menstrual phase-dependent differences in mucins suggests that mucin concentration and not composition changes in response to alterations in the hormonal milieu.     

Regulation of B lymphocyte activation by the Fc portion of immunoglobulin

Murine splenic B lymphocytes are induced to proliferate and undergo polyclonal activation in the presence of Fc fragments, AHGG, antigen-antibody complexes, and CH₃ fragments derived from plasmin digestion of human Ig. The unifying feature of the polyclonal antibody response induced by these agents is that in all cases a portion of the constant region of the Ig molecule (ie, Fc region) is present. Fragments of Ig lacking the Fc piece, such as Fab and F(ab′)₂ were found not to be stimulatory. In addition, a model is proposed to account for the regulatory effects of antigen-antibody complexes on an ongoing humoral immune response.     

Complete degradation of carbohydrate to carbon dioxide and methane by syntrophic cultures of Acetobacterium woodii and Methanosarcina barkeri

Methanosarcina barkeri (strain MS) grew and converted acetate to CO₂ and methane after an adaption period of 20 days. Growth and metabolism were rapid with gas production being comparable to that of cells grown on H₂ and CO₂. After an intermediary growth cycle under a H₂ and CO₂ atmosphere acetateadapted cells were capable of growth on acetate with formation of methane and CO₂. When acetate-adapted Methanosarcina barkeri was co-cultered with Acetobacterium woodii on fructose or glucose as substrate, a complete conversion of the carbohydrate to gases (CO₂ and CH₄) was observed.Abbreviation CMC carboxymethyl cellulose     

The action of proteolytic enzymes on chloroplast thylakoid membranes

Envelope- and stroma-free thylakoid membranes of Vicia faba chloroplasts were incubated with trypsin or pronase for several hours. The indigestible residue was analyzed by polyacrylamide gel electrophoresis. Trypsinization resulted in a complete digestion of all proteins with the exception of the pigment-protein complexes as well as a polypeptide not yet characterized. Yet, as compared with untreated material, Complex II was found to have higher electrophoretic mobility. Electron-microscopic studies illustrate that the indigestible residue still has a preserved membrane structure. Disintegration of the thylakoid membranes by sodium dodecyl sulfate followed by trypsinization also resulted in the two complexes while all the other proteins were found to be digested. However, after removal of the lipids the protein moieties of the complexes proved to be easily digestible. From these results it is concluded that pigment-protein interaction may be an important factor in maintaining a conformation rather resistant to perturbants and proteases. In contrast to trypsin, pronase completely digested the polypeptides of the thylakoid membranes including the protein moieties of the pigment-protein complexes leaving an amorphous lipid mass. The results support the assumption that the complexes are necessary to maintain the membrane structure.