Proton conductance of cell membranes

Several workers have suggested that cell membranes have a high proton conductance. Our interest in this concept arose from the possibility that the nutrient (submucosal-facing) membrane of the gastric mucosa may have a high proton or hydroxyl ion conductance which would play a role in the regulation of the acid-base balance of the cell. We found that wide changes in the H⁺ concentration of the fluid bathing the nutrient side of the in vitro frog gastric mucosa did not result in significant changes in p.d. However, a maintained change of the H⁺ concentration of the bathing fluid would be expected to produce only a temporary change in p.d. Since a diffusion barrier is present on the nutrient side the temporary change in p.d. might be masked. An analysis of this possibility was made on the basis of a conceptual model and as a result of the analysis it is concluded that the proton (and/or OH^?) conductance of the nutrient membrane of the frog gastric mucosa is not a significant fraction of its total conductance. The present status of the proton conductance hypothesis with respect to striated muscle and to the secretory membrane of the gastric mucosa is reviewed.     

Semicontinuous penicillin production by two Penicillium chrysogenum strains immobilized in calcium alginate beads

Summary The growth rates of immobilized Penicillium chrysogenum strains are important in their application to semicontinuous penicillin production. Immobilized P. chrysogenum strains produced about 10–15% less biomass but about 1–2 times more penicillin than free suspended mycelia.In a chemically defined medium an industrial P. chrysogenum strain, S₁, produced about 10–12 times more penicillin than strain ATCC 12690. In a complex medium the immobilized P. chrysogenum S₁ produced about 12% penicillin more than in shaken cultures. In bubble column fermentations, penicillin production was 163% higher in the complex medium than in the chemically defined medium.     

Microelectrode studies of potential difference responses to changes in stromal K+ in bullfrog cornea

The effects of changing stromal K+ were studied using microelectrodes in an in vitro preparation of frog cornea. The intracellular potential (V0) responded in two opposite ways under short-circuit conditions: (1) depolarization (normal response) when stromal K+ was increased from 4 to 20 or to 79 mM, about 30 mV per 10-fold K+ concn. change; (2) a hyperpolarization (anomalous response) of 10 mV maximum when stromal K+ was increased from 0 to 4 mM. The increase from 4 to 20 or 79 mM decreased or even reversed the short-circuit current (Isc). The transepithelial conductance (gt) increased when K+ was increased to 79 mM but no change occurred in the apical membrane fractional resistance (fRo). Increase of stromal K+ from 0 to 4 mM increased Isc and minimally changed gt and fRo. Ouabain (10(-3) M) abolished the anomalous responses, that is, the increases in V0 and Isc when stromal K+ was increased from 0 to 4 mM. These results are interpreted in terms of two K+ conductive pathways in the basolateral membrane of the corneal epithelium, a Nernstian conductance and an electrogenic (Na+ + K+)-ATPase pump transporting more Na+ than K+ ions per cycle. The normal or anomalous potential difference responses to changes in stromal K+ appear to depend on the relative resistance of the two pathways at the time stromal K+ is changed.     

Thrombin and C-kinase activators potentiate calcium-stimulated arachidonic acid release in human platelets.

Human platelets were depleted of intracellular Ca2+ and then made selectively permeable to external Ca2+ by addition of the ionophore ionomycin. In this cell system a rapid release of arachidonic acid was seen in direct response to added Ca2+ at concentrations corresponding to cytosolic Ca2+ levels measured in thrombin-stimulated platelets. Thrombin and other activators of Ca2+/phospholipid-dependent protein kinase (C-kinase) potentiated the Ca2+-stimulated arachidonic acid release while exerting little or no effect in the absence of added Ca2+. Agents which increase (R59022) or decrease (isoquinolinesulphonylmethylpiperazine) the activation of C-kinase correspondingly enhanced or inhibited, respectively, the potentiation of arachidonic acid release caused by thrombin. These results support the hypothesis that arachidonic acid release in human platelets is regulated by a co-operative action between intracellular Ca2+ and C-kinase.     

Influence of sucrose concentration and phosphate limitation on citric acid production by immobilized cells of Aspergillus niger

Summary Immobilized cells of Aspergillus niger needed a lower initial sucrose concentration than free cells in order to obtain maximal yields of citric acid production. High sucrose concentrations led to reduced yields and increased polyol formation (glycerol, erythritol, arabitol). Continuous fermentation with media containing low sugar concentrations prevented the formation of polyols. The change from nitrogen-limited to phosphate-limited precultivation of immobilized spores significantly increased the productivity of the mycelium. The ratio of citric acid to residual sugar in the effluent distinctly lay in the direction of citric acid. Inside the alginate beads mainly large bulbous cells were observed.     

Identification and production of Δ9-cis-1, 18-octadecenedioic acid by Candida tropicalis

Summary The production of ⁹-cis-1, 18-octadecenedioic acid from different substrates by the mutant S₇₆ of Candida tropicalis was studied. It was found that the mutant could convert oleyl alcohol, oleic acid, and methyl oleate to ⁹-cis-1, 18-octadecenedioic acid through either the diterminal oxidation of the alcohol or the -oxidation of the terminal methyl group of the mono acid. The geometric configuration of the product was identified by different analytical methods. The results demonstrated that no change in the geometric configuration of molecular structure happened during the bioconversion of such unsaturated substrates to ⁹-dioic acid. To enhance the production of this dioic acid in the medium, calcium carbonate was added as a trapping agent. The IR spectrum, ¹H NMR and ¹³C-satellite spectra of this compound were presented.Dedicated to Professor Dr. K. Esser on the occasion of his 65th birthday     

Degradation of phenol by a coimmobilized entrapped mixed culture

Summary The degradation of phenol by a defined mixed culture, consisting of Pseudomonas putida P8 and Cryptococcus elinovii H1, was studied. The microorganisms were entrapped either in 30 g·l^-1 calcium-alginate or in chitosan-alginate. Chitosan-alginate entrapment was suitable for a continuous culture. The coimmobilized mixed culture of Cryptococcus elinovii H1 which degrades phenol via an ortho pathway and of Pseudomonas putida P8 which uses the meta cleavage pathway was able to degrade high phenol concentrations up to 3.2 g·l^-1 in semicontinuous cultures. The degradation performance in continuous cultures could reach a maximum of 0.41 g·l^-1·h^-1 phenol. The mixed culture could be stored for up to six months without loss of phenol degradation capacity.Dedicated to Professor Dr. Dr. h. c. K. Esser on the occasion of his 65th birthday     

Immunological evidence for a relationship between the dendrotoxin-binding protein and the mammalian homologue of the Drosophila Shaker K+ channel

Polyclonal antibodies were raised against two synthetic peptides from different parts of the predicted amino acid sequence of the mouse homologue (MBK1) of the Drosophila Shaker K+ channel. The antibodies recognized the toxin-binding subunit of the dendrotoxin-binding proteins from rat and bovine brain. The results suggest that the dendrotoxin-binding protein is related to the expression products of the mammalian homologue of the Shaker gene.     

Oxidation of n-tetradecane by Candida parapsilosis KSh 21 adsorbed on different glass rings

Summary Living cells of Candida parapsilosis KSh 21 were immobilized by adsorption on different types of glass rings. The presence of n-tetradecane enhanced the cell adsorption especially on normal glass rings. The high adhesion of cellulose-coated glass rings and of sintered glass rings induced a quick adsorption of the cells. The quantity of 1-tetradecanol produced in the cultures of immobilized cells especially on SGR was higher than that of the free cells. Low numbers of free cells released in the immobilized cultures were observed. Better contact between the immobilized cells and oil droplets was noticed.     

Metal-binding proteins of the Syrian hamster ovaries: apparent deficiency of metallothionein

A deficiency of metallothionein, a high-affinity metal-binding protein thought to detoxify cadmium, has been observed in rat and mouse testes, tissues that are highly susceptible to the necrotizing and carcinogenic effects of cadmium. Like the testes, the ovaries undergo a hemorrhagic necrosis when exposed to cadmium, and female Syrian hamsters have recently been shown to be highly susceptible to cadmium. However, the nature of cadmium-binding proteins in the ovary is unknown; thus, this study was undertaken to define the nature of any such proteins in the Syrian hamster ovary. A low molecular weight (Mr) zinc- and cadmium-binding protein was detected in cytosol derived from the ovaries after gel filtration that eluted with a relative elution volume similar to authentic metallothionein. This protein was extractable by heat-treatment and sequential acetone precipitation. When such extracts were further purified with a reverse phase high performance liquid chromatography (HPLC) technique developed for the isolation of metallothionein isoforms, two forms were separated. However, neither of these could be classified as metallothionein on the basis of amino acid composition, since both were particularly low in cysteine, a very common amino acid in metallothionein. The ovarian protein also contained significant amounts of aromatic amino acids, unlike metallothionein--which is devoid of aromatics, and contained much more glutamate than metallothionein. Hamsters were also made resistant to cadmium-induced ovarian necrosis by zinc treatment. Such zinc treatment, however, did not alter levels of this protein, yet caused a marked induction of hepatic metallothionein. Likewise, cadmium treatment did not increase the levels of the ovarian metal-binding protein yet markedly induced hepatic metallothionein.(ABSTRACT TRUNCATED AT 250 WORDS)