Effect of added orthophosphate on pyrophosphate hydrolysis in soil

Summary The inhibition effect of orthophosphate on the rate of pyrophosphate hydrolysis in soil was investigated. Orthophosphate had a competitive inhibition on pyrophosphate hydrolysis in soil. However K'_m (apparent Michaelis constant) was greater than K_m (Michaelis constant) and V_max increased when orthophosphate was added.     

Effect of cell lipid composition on the formation of nonspecific antibiotic resistance in alkanotrophic rhodococci

The antibiotic resistance and lipid composition of rhodococci grown in rich organic media with gaseous or liquidn-alkanes were studied. Hydrocarbon-grown rhodococci exhibited an increased resistance to a wide range of antibiotics (aminoglycosides, linkosamides, macrolides, β-lactams, and aromatic compounds). The enhanced antibiotic resistance of rhodococci grown onn-alkanes correlated with an increased content of total cell lipids (up to 14–28%) and saturated straight-chain fatty acids (C_16:0, C_18:0, C_21:0) and was accompanied by the appearance of cardiolipin and phosphatidylglycerol in cells. These lipid compounds are supposed to promote the formation of nonspecific antibiotic resistance in rhodococci by decreasing the permeability of their cell envelope to antibiotics.     

Calculated minimum energy conformations of nonactin

Nonactin is a cyclic actinomycete metabolite which has been implicated as an ion carrier in the passive transport of potassium across certain biological membranes. In order to discover the conformations of the molecule which are involved in its biochemical function, computer calculations were initiated to derive the energetically favored conformations of the nonactin ring. By assuming that all the relevant three-dimensional conformations of nonactin have the same symmetry property as that suggested by the chemical structure of the molecule (S₄) it was possible to generate a representative sample of all sterically allowed conformations of nonactin. The energies of these conformations were calculated by taking into account the nonbonded interactions among the 116 atoms of the molecule and the torsional potential energy of the 20 rotatable backbone bonds of the ring. The initial results reported in this paper indicate that even in the absence of potassium ion the nonactin ring folds into the same compact tennis-ball seam-like conformation that was found by an X-ray crystallographic investigation of the nonactin/KNCS complex.     

Effect of metal cations on the formation of antibiotic and pigment by the mycophilic fungus Hypomyces rosellus 94/77

Using the method of mathematical planning of experiment the effect of calcium, magnesium, manganese, iron, zinc and copper on synthesis of antibiotic and pigment by mycophilic fungus Hypomyces rosellus has been studied. The ions of Mg2+, Mn2+, Fe2+ have been found to be important for antibiotic and pigment formation by fungus, the ions of Mg2+ and Mn2+ are interchangeable.     

Electronic and spatial structure of dimethyl orthophosphate and orthophosphate

The applicability of different variants of the semiempirical CNDO method to calculate the electronic structure of different conformations of all possible ionic forms of dimethyl orthophosphate and orthophosphate is considered. The CNDO/BW (Boyd-Whitehead parameterization) approximation with selected parameters for the P-O bond is shown to provide the best qualitative and sometimes quantitative agreement with ab initio methods. The dependences of energy and P-O bond strengths in P-O-CH₃ (P-O-H) groups on torsion angles at P-O bonds are obtained in this approximation for dimethyl orthophosphate and orthophosphate. The rotation of these groups is found to stremgthen one P-O bond stronger and labilize another. The energy minima of dimethyl orthophosphate and orthophosphate anions are shown to correspond to conformations where the strengths of the studied P-O bonds are almost the same, i.e., none of the bonds is weakened to a minimum. Protonation of these compounds increases the strength of P-O bonds and decreases the dependence of bond strength on torsion angles. The di-and trianions of dimethyl orthophosphate and orthophosphate are also studied. The growth of negative charge is shown to progressively weaken the P-O bond. The dependence of bond strength on torsion angle for the dianion is less pronounced than that for the monoanion. Calculation results are compared with experimental data known from literature. The significance of the data obtained for revealing essential features of the enzyme cleaving and forming the P-O bond is discussed.     

Effect of adenine nucleotides on the reaction catalyzed by pyruvate,orthophosphate dikinase in maize

The effect of adenine nucleotides in pyruvate, orthophosphate dikinase (EC 2.7.9.1, ATP, pyruvate, orthophosphate phosphotransferase)_was studied with the enzyme furified from maize, and with the enzyme obtained from mesophyll chloroplast extracts during assay in the direction of pyruvate conversion to phosphoenolpyruvate. (1) In studies with the purified enzyme, the relationship of initial velocity to ATP concentrations follows Michaelis-Menten kinetics, and the K_m value for ATP was 22.8 μM (± 5.1 μM, n = 5). (2) AMP was a competitive inhibitor with respect to ATP, and its K_i value was 35.8 μM (± μM, n = 4). There was no inhibition of catalysis by ADP up to a concentration of 460 μM. (3) The theoretical response of the enzyme to change in the adenylate energy charge was calculated from the kinetic constants for ATP and AMP. The experimentally obtained values were similar to the theoretical response when varying energy charge was generated by addition of appropriate amounts of ATP, ADP and AMP in assays with the purified enzyme. The response of the enzyme to energy charge at different pH values (pH 7.0, 7.5, and 8.0) was similar, although the activity of the enzyme at pH 7.0 was about 40% of that at pH 8.0. (4) When mesophyll chloroplast extracts of maize, which contain high levels of adenylate kinase, were used as the source of the enzyme and the adenylate energy charge was generated by addition of different concentrations of ATP and AMP, the influence on catalysis was similar to that with the purified enzyme. (5) The data show that the effect of varying energy chage on the activity of the dikinase is not typical of a U-type enzyme, in contrast to phosphoglycerate kinase (EC 2.7.2.3, ATP: 3-phospho-D-glycerate 1-phosphotransferase), which is more strongly regulated. (6) Evidence is presented for competition between the dikinase and phosphoglycerate kinase for ATP in mesophyll chloroplast extracts of maize. (7) When the effect of adenylate energy charge on the state of activation and the direct effect on catalysis of the dikanase are combined, the total capacity for catalysis is very dependent on the energy charge.     

Effect of orthophosphate on the rate of calcium uptake by red and white muscle sarcoplasmic reticulum

Summary In the presence of added orthophosphate (P_i) there is a period during which sarcoplasmic reticulum vesicles (SR) accumulate calcium at a constant rate. This constant rate is increased and is reached sooner when the added P_i concentration is increased. A double reciprocal plot of rate and P_i concentration gives a straight line.The P_i concentration required for half-maximum rate of calcium accumulation is the same for SR preparations from red and white rabbit muscles, although the maximum rates are widely different. During the ageing of SR preparations the P_i concentration required for half-maximum rate increases, but the maximum rate remains the same.     

Effect of alginate structure and microalgae immobilization method on orthophosphate removal from wastewater

Microalgae play an important role during the tertiary treatment of municipal wastewater. Cell immobilization techniques have been developed in order to improve the quality of the treated wastewater and avoid wash out of the biomass. Since cell immobilization method may affect the nutrient removal efficiency, ten strains of microalgae were immobilized in sodium alginate gel in different-diameter circular screens, and orthophosphate removal efficiency from municipal wastewater was studied. Results indicate that the alginate immobilization screen size and contact surface with wastewater affects the microalgae synthesis activity and thus orthophosphate removal efficiency. Increasing the contact surface by making smaller alginate screens will increase the cation exchange rate and reduce the orthophosphate concentration in the medium. Among all microalgae treatments, Scenedesmus rubescens MCCS 018, Chlamydomonas sp. MCCS 026, and Chroococcus dispersus MCCS 006 had the highest PO ₄ ^3- -P removal efficiency of 68.8%, 71.9%, and 72.3% within 12?days.     

Study of the effect of protoplast formation on the antibiotic activity of erythromycin producers

The influence of protoplasting and regeneration on the strains of the erythromycin-producing organism differing by their origin was studied with respect to changes in the antibiotic production property. 223 regenerates of the erythromycin-producing culture were tested in several generations and it was shown that there was a marked change in the range of the variation by that property. 40 to 70 per cent of the variants in the IInd generation increased their levels of erythromycin biosynthesis by 20 to 60 per cent as compared to the intact cultures. However, in the subcultures the antibiotic production level decreased and by the IVth generation only 3 to 6 per cent of the variants preserved its increase by 10 to 20 per cent over the control level because of the culture high instability.     

Effect of fasting and insulin on the glucagon-induced orthophosphate incorporation to the isolated perfused rat liver.

Isolated perfused fed rat livers spontaneously liberated glucose and orthophosphate to the medium; 24-hr fasted rat livers did not exhibit these phenomena. In perfused fed rat livers, glucagon (2 mug) increased glucose output and promoted orthophosphate incorporation. In perfused fed rat livers, insulin (250 or 500 mU) inhibited the spontaneous liberation of glucose and orthophosphate. Comparable doses of insulin significantly reduced the glucagon (2 mug)-induced increase in glucose output from perfused fed rat liver, but did not affect orthophosphate uptake by the organ.