Nucleotide pyrophosphatase of rat liver. A comparative study on the enzymes solubilized and purified from plasma membrane and endoplasmic reticulum.

Studies on the subcellular distribution of rat liver nucleotide pyrophosphatase activity revealed its presence in the plasma membrane and the endoplasmic reticulum only. The enzymes from either source were solubilized specifically with trypsin without an apparent change of their catalytic properties. A 200-fold and 1600-fold purification, respectively, was achieved by a procedure including DEAE-cellulose and affinity-chromatography with AMP as ligand, gel filtration on Sephadex G-200 and gel electrophoresis. Both nucleotide pyrophosphatases were isolated as electrophoretically homogeneous soluble proteins. They were shown to contain carbohydrate moieties. The electrophoretic mobility of both enzymes in polyacrylamide gels was identical at three pH values. Dodecylsulfate gel electrophoresis indicated a molecular weight of 137 000 for both glycoproteins. The enzymes hydrolyze a variety of purine and pyrimidine nucleotides yielding a 5'-nucleoside monophosphate. Adenosine 3':5'-monophosphate, nucleic acids and phosphate monoesters are not cleaved, but p-nitrophenyl-thymidine5'-monophosphate is readily hydrolyzed. In view of their substrate and inhibitor specificities the enzymes are considered nucleotide pyrophosphatases rather than phosphodiesterases.     

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.     

Effect of Salt Stress on Viability, Germination and Endogenous Levels of Some Metabolites and Ions in Maize (Zea mays L.) Pollen

Maize plants, subjected to 0, 80, 120 and 160 meq l^–1salinity using NaCl, showed adverse effects on viability, germinationand tube growth of pollen, besides enhancing the bursting ofpollen. The endogenous levels of various metabolites in pollenwere also affected. Pollen grains from salinized plants hadmore soluble carbohydrates, free amino acids, especially proline,phenols and DNA and less starch, protein and RNA compared tothe non-saline controls. Salinity also resulted in the accumulationof ions such as Na⁺, K⁺ and Cl^– while it caused a reductionin the boron content of pollen. These metabolic disturbancespossibly lead to decreased viability, germination and tube growthof pollen thereby resulting into a reduction in reproductivecapacity of the plants under salt stress. Zea mays L., maize, pollen, viability, germination, salt stress     

Potential sites of geosmin production by streptomycetes in and around reservoirs

Water from several oligotrophic reservoirs of the North West Water Authority at Longridge, Lancashire, supported only sparse growth of streptomycetes isolated from the reservoirs. Growth was enhanced by nutrient-amendment of the water and one common isolate, identified as Streptomyces albidoflavus , produced geosmin in water which was supplemented with sufficient concentrations of available carbon, nitrogen and phosphorus. The minimum concentrations required for geosmin production were higher than those recorded in natural reservoir water. Synthesis of geosmin in water also required a minimum temperature of about 15dEC. Sterilized samples of reservoir sediment, sediment extract, plant debris from banks and surrounding soil also supported geosmin production by S. albidoflavus. Both bank debris and exposed sediment developed earthy odours without inoculation. The structure of reservoir banks influenced the quantity of plant growth and accumulation of litter, and therefore also the potential for contamination of reservoir water by geosmin. The potential of these various sites of geosmin production to contaminate reservoir water is assessed.