Effects of increased salinity on the diatom assemblage in Fonda Lake,Michigan

A salt storage facility has been located adjacent to Fonda Lake since 1953. In February 1981 a core was taken from the profundal sediments of the lake and analyzed to determine the effects of salt perturbation on the diatom community over a 32-year period. Diatom assemblages from different levels were compared using multivariate techniques including cluster analysis and principal component analysis. Shifts in diatom composition related to salinification were revealed most clearly by subdominant taxa. Five distinct groups of diatom taxa were found to correspond with 5 depth intervals. The diatom component of the lake up to 1960 included two groups of taxa which were alkaliphilous and chloride indifferent. A reduction in species diversity beginning in 1960 may indicate a salt effect. By 1968, when diversity reached a minimum, a variety of halophilic taxa (including Diatoma tenue, Navicula gregaria and Synedra fasciculata) attained their highest relative abundances. At the top of the core, diversity increased slightly and some halophilic taxa decreased in relative abundance, which suggests a possible decrease in salt loading to the lake.     

Effects of starvation on growth and reproductive apparatus of two immature freshwater snails Biomphalaria pfeifferi and Biomphalaria glabrata (Gastropoda: Planorbidae)

Starvation of immature snails of Biomphalaria pfeifferi and B. glabrata results in an arrest of growth and animals remain immature. Spermatogenesis is limited to spermatogonia (B.g.) or spermatocytes 1 (B.p.). The number and the size of oocytes remain inferior to that of controls. Animals show reduced genital tracts.Once feeding is restored, growth is resumed but wet weight and shell diameter do not reach the same level as in controls. Fecundity and gametogenesis do not differ from that in controls. Genital tracts weight is proportional to body weight.     

A kinetic model for the hydrolysis and synthesis of maltose, isomaltose, and maltotriose by glucoamylase

Kinetic results on the glucomylase-catalysed hydrolysis of maltose and maltotriose, and glucose polymerization into maltose and isomaltose up to 450 g/L total sugar concentration are presented. Whereas the enzyme has a faster hydrolytic and synthetic activity on alpha-(1-->4) than on alpha-(1-->6) linkages, at equilibrium, on the contrary, the isomaltose level which represents 15% (w/w) of the total sugar concentration at the highest investigated concentrations is much higher than the corresponding maltose level. Under a wide range of initial conditions, experimental results are adequately described by a new kinetic model with simple first- and second-order, or Michaelian-type, rate expressions for the reversible hydrolysis of maltotriose, maltose, and isomaltose. The model also accounts for the inhibition of hydrolysis by glucose, but does not consider the concentration of water which, under the present conditions, was not found kinetically limiting.     

Cellobiose metabolism in Erwinia: genetic study

Summary The study of mutants of Erwinia specifically unable to ferment cellobiose indicates that the mutations are clustered between arg and ile on the chromosome of this organism. In vivo cloning of the genes responsible for cellobiose utilization lead to a plasmid, pBEC2, which complements all Erwinia Clb^- specific mutants. When introduced into wild-type E. coli it allows this organism to use cellobiose, arbutin and salicin; it also complements bglB and bglC mutants of Escherichia coli indicating that arbutin and salicin utilization is due to the products of the pBEC2 cloned genes. From the characterization of mutants pleiotropically affected in the utilization of various carbon sources, including cellobiose, arbutin and salicin, it is proposed that the three--glucosides are substrates of the phosphoenolpyruvate-dependent phosphotransferase system (PTS).     

Mesenchymal-epithelial conversions induced by 5-Azacytidine: Appearance of cytokeratin Endo-A messenger RNA

When mouse-teratocarcinoma-derived fibroblasts (1246 cell line) are subjected to treatment with the inhibitor of DNA methylation, 5-Azacytidine (5 AzaC), they transiently express at 55-kilodalton intermediate-filament protein recognized by the epithelial-specific monoclonal antibody, TROMA-1, although they retain a fibroblastic morphology. However, rare clones (e.g., the 1339 cell line) that permanently express the antigen recognized by TROMA-1 can be derived from the 5 AzaC-treated 1246 population, and these clones have an epithelial phenotype. In the present study, we used cloned DNA probes to demonstrate that, in 1246 fibroblasts, 5 AzaC induces the appearance of Endo-A mRNA. High levels of Endo-A mRNA were also detected in the epithelial derivative, cell line 1339. In both cases, the capping site of the Endo-A mRNA was found to be the same as that in epithelial cells which normally express this RNA.     

A jump in an Arrhenius plot can be the consequence of a phase transition. The binding of ATP to myosin subfragment 1

The temperature dependence of the kinetics of the binding of ATP to myosin subfragment-1 was studied by an ATP chase technique in a rapid-flow-quench apparatus: (formula; see text) A temperature range of 30 degrees C to -15 degrees C was obtained with ethylene glycol as antifreeze. The Arrhenius plot of k2 is discontinuous with a jump at 12 degrees C. Above the jump delta H+ = 9.5 kcal/mol, below delta H+ = 28.5 kcal/mol. Few such Arrhenius plots are recorded in the literature but they are predicted from theory. Thus, we explain our results as a phase change of the subfragment 1-ATP system at 12 degrees C. This is in agreement with certain structural studies.     

A kinetic model of starch hydrolysis by alpha- and beta-amylase during mashing

Kinetics of malt starch hydrolysis by endogeneous alpha- and beta-amylases has been experimentally investigated in laboratory-, pilot- and industrial-scale reactors. The production rates of glucose, maltose, maltotriose and total extract, and the separate alpha- and beta-amylases deactivation rates are measured at varying mashing temperature and different initial starch concentrations and qualities. Based on the experimental results, a model is proposed that takes into account the initial carbohydrates and enzymes dissolution, the starch gelatinization, the separate hydrolytic action of alpha-and beta-amylases on insoluble and soluble starch and dextrins, and the influence of temperature both on enzyme activities and thermal denaturation rate. The model can predict, at the three scales, the final sugars concentrations in the wort for given initial malt concentrations and enzymatic contents, and for a fixed temperature profile during the mashing process.     

Theoretical conformational analysis of phospholipids II. Role of hydration in the gel to liquid crystal transition of phospholipids

To obtain a satisfactory agreement between computed transition temperatures and those determined experimentally, we introduce explicitly water molecules which hydrate the polar headgroup of dipalmitoylphosphatidylethanolamine molecules. The calculated free energy curves as a function of the intermolecular interchain distance and the degree of hydration of the polar groups permit the determination of the transition of the phospholipid system from the gel to the liquid crystalline phase. The detailed structure of the hydration shell is defined using the supermolecular approach.     

NAD+-induced inhibition of phosphate transport in canine renal brush-border membranes Mediation through a process other than or in addition to NAD+ hydrolysis

We previously demonstrated inhibition of Na⁺-dependent ³²P_i transport in canine renal brush-border membranes in association with NAD⁺-induced ADP ribosylation of membrane protein(s) and postulated that NAD⁺ inhibits P_i transport across the brush-border membrane via ADP ribosylation. Recently it was shown that incubation of rat brush-border membrane with NAD⁺ resulted in release of P_i which was prevented by EDTA. It was proposed that NAD⁺-mediated inhibition of ³²P_i transport might occur through this mechanism. To determine whether NAD⁺ inhibited ³²P_i transport by a mechanism other than or in addition to release of P_i, we compared Na⁺-dependent ³²P_i counterflow in brush-border membrane equilibrated with P_i or with P_i generated from NAD⁺. Release of P_i from NAD⁺ incubated with brush-border membrane was confirmed. The increased uptake of ³²P_i which was demonstrated in brush-border membrane equilibrated with P_i was not measured when intravesicular P_i was generated from a concentration of NAD⁺ which effected ADP-ribosylation of brush border membranes (100 μM NAD⁺). In contrast, increased uptake of ³²P_i was demonstrated when intravesicular P_i was generated from 1 μM NAD⁺ which did not effect ADP ribosylation. Mg²⁺-dependent ADP ribosylation of brush-border membrane incubated with NAD⁺ was demonstrated which persisted during the time interval of ³²P_i uptake measurements. Our findings are compatible with the hypothesis that NAD⁺-induced ADP ribosylation of brush-border membrane protein(s) results in inhibition of P_i transport across the membrane in vivo. EDTA may act to prevent this inhibition in brush-border membrane by chelation of Mg²⁺ and decreased ADP ribosylation.