The Presence of a Ribonuclease of High Molecular Weight in Sugar Beet Storage Tissue

Soluble ribonuckasie activity in sliced root tissue or sugar beet (Beta vulgaris) decreased to 30% of initial levels during the first 15 hours of aeration in sterile phosphate buffer. Activity increased with continued aeration reaching a maximum at 30 hours (85% of initial levels). Ribonuclease activity was isolated from unaerated tissue and partially purified by precipitation with acid and ammonium sulfate and by Sephadex chromatography. Enzyme activity was linear with respect to enzyme and substrate concentrations. The enzyme exhibited a substrate preference for RNA with no activity in the presence of native or denatured DNA. Elution of the enzyme from a Sephadex G-150 column indicated a molecular weight of 155,000. This uniquely large ribonuclease had no phosphodiesterase activity, was unaffected by ethylenediamine tetraacetate, and was inhibited by increasing Nig²⁺ concentrations.     

The role of free serum tryptophan in the biphasic effect of acute ethanol administration on the concentrations of rat brain tryptophan, 5-hydroxytryptamine and 5-hydroxyindol-3-ylacetic acid.

1. Acute administration of ethanol exerts a biphasic effect on the concentrations of rat brain tryptophan, 5-hydroxytryptamine and 5-hydroxyindol-3-ylacetic acid. Both effects are associated with corresponding changes in the availability of circulating free tryptophan. 2. The initial increases in the above concentrations are prevented by ergotamine, are unaltered by allopurinol and are potentiated by theophylline, whereas the later decreases are prevented by both ergotamine and allopurinol. 3. It is suggested that the initial enhancement by ethanol of brain tryptophan metabolism is caused by catecholamine-mediated lipolysis followed by displacement of protein-bound serum tryptophan, whereas the activation of liver tryptophaan pyrrolase, which is produced by the same mechanism, leads to the later decreases in the brain concentrations of tryptophan and its metabolites. 4. The initial effects of ethanol can be reproduced by an equicaloric dose of sucrose, and a comparison of the two treatments alone could therefore be misleading. 5. The effects of ethanol on liver and brain tryptophan metabolism have also been examined in mice, and a comparison of the results with those previously reported suggests that the ethanol effects are strain-dependent.     

The regulation of potassium absorption in barley roots

The dynamics of changes in K(+) influx across the plasmalemma and of internal K(+) concentrations [K(+)](1) of intact barley (Hordeum vulgare) roots were examined as the roots were converted from ;high-salt' to ;low-salt' roots. Following the transfer of plants grown in 0.5 mm CaSO(4) solutions plus various concentrations of KCl to 0.5 mm CaSO(4) solutions, influx rates increased and internal K(+) concentrations declined as a function of time and the initial K(+) status of the tissue. The relationship between plasmalemma influx and [K(+)](1) was examined over a wide range of [K(+)](1) values by growing intact plants in various concentrations of KCl. Plasmalemma influx was inversely correlated with the square of [K(+)](1). A model for the regulation of plasmalemma influx by [K(+)](1) is considered.     

Multiphasic kinetics of transformation of 1,2,4-trichlorobenzene at nano- and micromolar concentrations by Burkholderia sp. strain PS14

The transformation of 1,2,4-trichlorobenzene (1,2,4-TCB) at initial concentrations in nano- and micromolar ranges was studied in batch experiments with Burkholderia sp. strain PS14. 1,2,4-TCB was metabolized from nano- and micromolar concentrations to below its detection limit of 0.5 nM. At low initial 1,2,4-TCB concentrations, a first-order relationship between specific transformation rate and substrate concentration was observed with a specific affinity (a(0)(A)) of 0.32 liter. mg (dry weight)(-1). h(-1) followed by a second one at higher concentrations with an a(o)(A) of 0.77 liter. mg (dry weight)(-1). h(-1). This transition from the first-order kinetics at low initial 1,2,4-TCB concentrations to the second first-order kinetics at higher 1,2,4-TCB concentrations was shifted towards higher initial 1,2,4-TCB concentrations with increasing cell mass. At high initial concentrations of 1,2,4-TCB, a maximal transformation rate of approximately 37 nmol. min(-1). mg (dry weight)(-1) was measured, irrespective of the cell concentration.     

The Effect of Urea on Acid Phosphatase Deactivation

Acid phosphatase thermal deactivation follows a complex path consisting of an initial decay of the native enzyme towards an equilibrium distribution of two intermediate structures, mutually at equilibrium. This initial transition is followed by a final decay towards a completely inactive enzyme configuration.

All the relevant parameters (one equilibrium and two kinetic constants) of the phenomenon are environment-sensitive. It is shown that urea affects the deactivation, by increasing the rate of both structural transitions as well as the thermodynamics of the equilibrium between intermediate forms. For every urea concentration up to 2.4M, an equivalent temperature can be calculated that yields exactly the same activity versus time profile. The result suggests that enzyme deactivation is controlled by a single parameter. Entirely different environments, so long as they result in the same value of the latter, are therefore bound to produce the same deactivation profile.

Marked deviations from thermal equivalence become apparent at higher urea concentrations. Therefore, extremely high urea concentrations seems to give rise to a change in the deactivation mechanism.     

The starch-binding domain from glucoamylase disrupts the structure of starch

The full-length glucoamylase from Aspergillus niger, G1, consists of an N-terminal catalytic domain followed by a semi-rigid linker (which together constitute the G2 form) and a C-terminal starch-binding domain (SBD). G1 and G2 both liberate glucose from insoluble corn starch, although G2 has a rate 80 times slower than G1. Following pre-incubation of the starch with SBD, the activity of G1 is uniformly reduced with increasing concentrations of SBD because of competition for binding sites. However, increasing concentrations of SBD produce an initial increase in the catalytic rate of G2, followed by a decrease at higher SBD concentrations. The results show that SBD has two functions: it binds to the starch, but it also disrupts the surface, thereby enhancing the amylolytic rate.     

The effects of glucose and oxygen on the cytochromes and metabolic activity of yeast batch cultures. II. Candida utilis

Candida utilis was grown in batch culture with and without oxygen control. The concentrations of A-, B-, and C-type cytochromes were found to vary with the initial glucose concentration, with the dissolved oxygen concentration, and with time. A-type was the most sensitive. After glucose was essentially exhausted, the yeast catabolized ethanol, if it had been growing in a relatively low initial glucose concentration, or non-glucose carbohydrate, including some of that previously accumulated within the cell, if it had been growing in a high initial glucose concentration. This difference in metabolic pattern could explain why cytochrome derepression was initiated soon after glucose uptake ceased only if initial glucose had been relatively low. The effects of glucose and dissolved oxygen concentrations on yeast cytochromes and respiratory activity are discussed.     

The concentration dependence of the depolarization of yeast by monovalent cations.

Monovalent cations decrease the initial rate of uptake of the membrane potential probe 2-(dimethylaminostyryl)-1-ethyl-pyridinium (DMP) into metabolizing cells, showing that the cells are depolarized. A steep decrease in this rate was found even at low cation concentrations, reaching 62%, 42%, 58%, 40% and 40% at high concentrations of K+, Rb+, Cs+, Na+ and Li+, respectively. The corresponding concentrations at which half-maximum decrease was found were 0.22, 0.36, 1.2, 17 and 17 mM. These values are of the same order of magnitude as the half-saturation concentrations for monovalent cation uptake by the yeast.     

Importance of Initial Concentration of Factor VIII in a Mechanistic Model of In Vitro Coagulation

This computational study generates a hypothesis for the coagulation protein whose initial concentration greatly influences the course of coagulation. Many clinical malignancies of blood coagulation arise due to abnormal initial concentrations of coagulation factors. Sensitivity analysis of mechanistic models of blood coagulation is a convenient method to assess the effect of such abnormalities. Accordingly, the study presents sensitivity analysis, with respect to initial concentrations, of a recently developed mechanistic model of blood coagulation. Both the model and parameters to which model sensitivity is being analyzed provide newer insights into blood coagulation: the model incorporates distinct equations for plasma-phase and platelet membrane-bound species, and sensitivity to initial concentrations is a new dimension in sensitivity analysis. The results show that model predictions are most uncertain with respect to changes in initial concentration of factor VIII, and this hypothesis is supported by results from other models developed independently.     

The dispersal of an initial concentration of motile bacteria.

The dispersal of an initial concentration of identical Brownian particles is accurately described by the solution of the conventional diffusion equation, and a diffusion coefficient can be assigned to the assembly of particles. However, the dispersal of an initial concentration of motile bacteria is not well described by the same solution, in spite of the similarity between the random motion of a bacterium and a Brownian particle. Reasons for the failure of the Gaussian solution of the diffusion equation to describe the dispersal of Escherichia coli are discussed. An equation is formulated which gives the concentration of dispersing organisms as a function of space and time if the speed distribution function of the assembly of organism is known and reproduction is suppressed. For three assumed speed distributions the results are compared with concentrations measured by previous authors.     

The gastrin-secreting effects of the salt components of naftusia water]

Intragastric administration of certain salt components of mineral water naftusia in minimal concentrations (1-5 mmol/l) changes intensity and direction of hypergastrinemic reaction in the rats. The effect is determined by the anionic composition of salts rather than by the cationic one and depends on the initial concentration of gastrin in blood.     

The influence of limiting and non-limiting growth conditions on glucose and maltose metabolism in Lactococcus lactis ssp. lactis strains

Three strains of Lactococcus lactis ssp. lactis, a dairy strain 65.1, a type strain ATCC 19435, and a mutant AS 211, were grown on glucose and on maltose under chemostat conditions. When the culture was shifted from glucose-limiting to non-limiting conditions, the product shifted from mixed acids to lactate. Mixed acids were obtained in all maltose cultures; however, an enhanced lactate formation was observed in 19435 and AS 211. An inorganic-phosphate (P_i)-dependent maltose phosphorylase activity was found to be responsible for the initial conversion of maltose. The activation of maltose phosphorylase by Pi was strain-specific. When growth was on maltose under non-limiting conditions, a correlation was found between high initial maltose phosphorylase and -phosphoglucomutase activities and lactate production. No such correlation was observed in maltose-limited cells. In glucose-grown cells under non-limiting conditions, homo-fermentative lactate formation coincided with high concentrations of fructose 1,6-bisphosphate (Fru1,6P ₂) and pyruvate (Pyr) and low concentrations of phosphoenolpyruvate (PPyr). Under limiting conditions, mixed acid formation coincided with low concentrations of Fru1,6P ₂ and Pyr and high concentrations of PPyr. In maltose-grown cells there was no correlation between intracellular intermediary metabolite concentrations and product formation. Therefore, in addition to intracellular intermediary metabolite concentrations, the product formation on maltose is suggested to be regulated by the transport and initial phosphorylating steps.     

The Chlorate-Iodine-Nitrous Acid Clock Reaction

A new clock reaction based on chlorate, iodine and nitrous acid is presented. The induction period of this new clock reaction decreases when the initial concentrations of chlorate, nitrous acid and perchloric acid increase, but it is independent on the initial iodine concentration. The proposed mechanism is based on the LLKE autocatalytic mechanism for the chlorite-iodide reaction and the initial reaction between chlorate and nitrous acid to produce nitrate and chlorite. This new clock reaction opens the possibility for a new family of oscillating reactions containing chlorate or nitrous acid, which in both cases has not been observed until now.     

Effect of phosphate on the biosynthesis of nourseothricin by Streptomyces noursei JA 3890b

The results present evidence for the important role of phosphate-mediated regulation of the nourseothricin biosynthesis by the processes of phosphate limitation and release of phosphate. Also, higher initial concentrations of phosphate were found to have a strong inhibitory effect on the biosynthesis of nourseothricin. It is concluded that the initial phosphate concentration was the primary target for the biometrical optimization of the fermentation medium. The presence of zinc ions neutralized the negative effect of high initial concentrations of phosphate which was also strongly influenced by the regime of sterilization.     

An on-line method for the collection and analysis of quasi-steady-state kinetic data for enzyme-catalyzed reactions.

A special mixing device for initiating enzyme-catalyzed reactions is used to rapidly achieve an unperturbed quasi-steady state. An on-line computer is employed to sample the initial conditions, the mixing time, and concentrations that change as a function of time during this quasi-steady state phase. A statistical method for estimating initial, quasi-steady state rates from the time course of the enzyme-catalyzed reaction is described. Practical considerations for using this parameter estimation system lead to the conclusion that for the enzyme-catalyzed reaction tested, the extent overall reaction should be above .2% for high initial substrate concentrations, and above 1% for initial substrate concentrations in the range of the Michaelis constant. Application of this method to a typical enzyme-catalyzed reaction suggests that objective estimates of initial rates from a given set of concentrations and corresponding times can be obtained with a standard error in the range of 2–3%, but that reproducibility is not better than about 10%. When this procedure was used to estimate initial rates for the glycerol dehydrogenase-catalyzed oxidation of glycerol by NAD, it was found that this enzyme did not behave according to the classical “Michaelis-Menten” mechanism of enzyme action.     

The role of a protonmotive force in genetic transformation of Bacillus subtilis]

The hypothesis on the role of protonmotive force in the transport of DNA through the membrane of Bac. subtilis cell during initial stages of genetic transformation was tested. A genetic transformation of arsenate-treated cells was observed. Treatment of cells by the protonophorous uncoupler of oxidative phosphorylation-carbonylcyanide dichlorophenyl--hydrazone-led to the inhibition of initial stages of genetic transformation having no significant effect on the level of intracellular ATP concentration and on the viability of cells. The dissipation of protonmotive force by means of K+ and H+ fluxes catalyzed by valinomycin and nigericin also caused the inhibition of initial stages of genetic transformation. The inhibitory effect of cationic penetrant tetraphenyl phosphonium was observed, the effect being potentiated by low concentrations of anionic penetrant phenyldicarbaundecaborate. The value of the membrane potential in the energized valinomycin-treated cells calculated from the distribution of K+ was within the range of 70--100 mV (inside minus). These results support the conception that a protonmotive force drives DNA transport through the membrane of Bac. subtilis cells.     

The effects of cadmium on zinc absorption in isolated rat intestinal preparations

The effect of cadmium on zinc absorption was studied using an isolated vascularly and luminally perfused rat intestinal preparation.⁶⁵Zn as well as Zn and Cd (both as the chloride salt) were added to the luminal perfusion medium (LPM) at varying concentrations. Over a 90-min period, the amount of Zn appearing in the vascular perfusion medium (VPM) and that retained by the tissue post-perfusion was estimated. Cd at all levels studied (0.03, 0.10, 1.0, and 10.0 μg/mL) reduced the amount of Zn appearing in the VPM in comparison with control perfusions (no detectable Cd in the LPM) when the initial Zn concentration was 5 μg/mL. Similarly, with an initial Zn concentration of 10 or 20 μg/mL, the amount of Zn appearing in the VPM was reduced when the Cd concentration was 0.1 or 1.0 μg/mL. With these same Zn concentrations, the amount of Zn retained by the tissue was higher when the Cd concentration was 10 μg/mL. These results demonstrate that Cd at low concentrations is capable of reducing Zn appearance in the VPM.     

The amiloride sensitive Na+/H+ antiport in guinea pig pancreatic acini. Characterization and stimulation by caerulein

Amiloride and analogs decrease the initial rate of 22Na+ uptake by dispersed acini from guinea pig pancreas in a dose-dependent manner. The initial rate of amiloride-sensitive 22Na+ uptake depends on external Na+ and H+ concentrations and on internal pH. These results provide evidence for the existence of a Na+/H+ antiport in pancreatic acinar cells. Caerulein, a cholecystokinin analog, stimulates the activity of the Na+/H+ antiport.     

Application of a reaction model to improve calculation of the sugar recovery standard for sugar analysis

A kinetic model was applied to improve determination of the sugar recovery standard (SRS) for biomass analysis. Three sets of xylose (0.10-1.00 g/L and 0.999-19.995 g/L) and glucose (0.206-1.602 g/L) concentrations were measured by HPLC following reaction of each for 1 h. Then, parameters in a kinetic model were fit to the resulting sugar concentration data, and the model was applied to predict the initial sugar concentrations and the best SRS value (SRS(p)). The initial sugar concentrations predicted by the model agreed with the actual initial sugar concentrations. Although the SRS(e) calculated directly from experimental data oscillated considerably with sugar concentration, the SRS(p) trend was smooth. Statistical analysis of errors and application of the F-test confirmed that application of the model reduced experimental errors in SRS(e). Reference SRS(e) values are reported for the three series of concentrations.     

The mode of action of lipid-soluble antioxidants in biological membranes: relationship between the effects of ubiquinol and vitamin E as inhibitors of lipid peroxidation in submitochondrial particles.

The effects of ubiquinol and vitamin E on ascorbate- and ADP-Fe3+-induced lipid peroxidation were investigated by measuring oxygen consumption and malondialdehyde formation in beef heart submitochondrial particles. In the native particles, lipid peroxidation showed an initial lag phase, which was prolonged by increasing concentrations of ascorbate. Lipid peroxidation in these particles was almost completely inhibited by conditions leading to a reduction of endogenous ubiquinone, such as the addition of succinate or NADH in the presence of antimycin. Lyophilization of the particles followed by three or four consecutive extractions with pentane resulted in a complete removal of vitamin E and a virtually complete removal of ubiquinone, as revealed by reversed-phase high pressure liquid chromatography. In these particles, lipid peroxidation showed no significant lag phase and was not inhibited by either increasing concentrations of ascorbate or conditions leading to ubiquinone reduction. Treatment of the particles with a pentane solution of vitamin E (alpha-tocopherol) restored the lag phase and its prolongation by increasing ascorbate concentrations. Treatment of the extracted particles with pentane containing ubiquinone-10 resulted in a restoration of the inhibition of lipid peroxidation by succinate or NADH in the presence of antimycin, but not the initial lag phase or its prolongation by increasing concentrations of ascorbate. Malonate and rotenone, which prevent the reduction of ubiquinone by succinate and NADH, respectively, abolished, as expected, the inhibition of the initiation of lipid peroxidation in both native and ubiquinone-10-supplemented particles. Reincorporation of both vitamin E and ubiquinone-10 restored both effects.(ABSTRACT TRUNCATED AT 250 WORDS)