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PubMedDate not supplied

[Reduction of respiration and glucose uptake by bacteria after lyophilization].

The techniques of delayed fluorescence and potentiometry were used to study the restoration of respiration and the rate of glucose assimilation by E. coli M-17 rehydrated after lyophilization in various dehydrating media. The activity of respiration and the rate of glucose assimilation decreased after lyophilization, particularly if the cells were freeze-dried without protecting agents. The restoration of respiration and glucose assimilation to the stationary level took 20--60 min after rehydratation. The stationary level was lower than the level of respiration and glucose assimilation before lyophilization. The decrease in respiration and glucose assimilation after lyophilization correlated with the determination of the number of viable cells by the culturing technique only for effective protecting media, viz. sucrose-gelatin and milk. The absence of such a correlation for cells dehydrated in media with low-effective protecting properties is presumed to be due to their synthetic processes being disturbed and genetic damages.

Bacteria↗

PubMed1980

Metal ion/buffer interactions. Stability of binary and ternary complexes containing 2-[bis(2-hydroxyethyl)amino]-2(hydroxymethyl)-1,3-propanediol (Bistris) and adenosine 5'-triphosphate (ATP).

The acidity constant of protonated 2-[bis(2-hydroxyethyl)amino]-2(hydroxymethyl)-1,3-propanediol (Bistris) has been measured. The influence of hydroxo groups on the basicity of Bistris and related bases is discussed. The interaction of Bistris with the metal ions (M2+) Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+ was studied by potentiometry and spectrophotometry in aqueous solution (I = 1.0 M, KNO3; 25 degrees C) and the stability constants of the M(Bistris)2+ complexes were determined. Unexpectedly Ca(Bistris)2+ is the most stable among the alkaline earth ion complexes (log KCaCa(Bistris) = 2.25; the corresponding values for the Mg2+, Sr2+ and Ba2+ complexes are 0.34, 1.44 and 0.85, respectively). The ions of the 3d series follow the Irving-Williams sequence: log KMnMn(Bistris) = 0.70, for Cu2+, 5.27 and Zn2+ 2.38. Ternary complexes containing ATP4- as a second ligand were also investigated: the values for delta log KM (= log KM(ATP)M(ATP)(Bistris) -log KMM(Bistris) are in general negative (e.g. delta log KCa = -0.40 or delta log KCu = -1.65), thus indicating that the interaction of Bistris with M(ATP)2- is somewhat less pronounced tan with M2+. However, even in mixed-ligand systems, complex formation may still be considerable, hence great reservations should be exercised in employing Bistris as a buffer in systems containing metal ions. Moreover, in several cases delta log KM is relatively high [for Mg2+-ATP4- -Bistris even positive], indicating some cooperativity between the coordinated ligands, possibly hydrogen-bond formation. Distributions of the complexes in dependence on pH are given, and the structures of the binary M(Bistris)2+ and the ternary M(ATP) (Bistris)2- complexes are discussed. The participation of Bistris hydroxo groups in complex formation is evident.

Adenosine Triphosphate↗

PubMedDate not supplied

[Role of water in the thermal instability of DNA].

We studied structural changes of DNA heated for long times at temperatures between 20 to 100 degrees C at different relative humidities (range 0--100%). DNA structure was analyzed by the following criteria: solubility changes, optical melting, ultraviolet spectroscopy, potentiometry and equilibrium dialysis. It has been found that irreversible changes in DNA secondary structure take place at around 37 degrees C, temperature optimal for the function in many living systems. These irreversible changes may be interpreted as a consequence of formation of interchain contacts (non-covalent "cross-links"). We demonstrate that the whole range of relative humidities may be divided onto three regions. For each of these regions DNA has somewhat different molecular structure and peculiarities are observed in the stabilizing and destabilizing action of water on DNA three-dimensional structure. Irreversible changes of DNA secondary structure as a function of bound water are represented by a bell-shaped curve. Similarity between this curve and a curve for the survival microorganisms is discussed.

DNA↗

PubMed1993

Automated enzymatic determination of sodium in serum.

An automated method based on the principles of flow-injection analysis is proposed for the enzymatic determination of sodium ion in serum. The method relies on the activation of beta-galactosidase by the analyte. The features of the proposed method include linear range between 1 and 1700 mumol/L, a sampling rate of 50 samples/h, a sample volume of 50 microL, and the absence of interferences from species usually present in serum. The results obtained were consistent with those provided by widely used methods such as those based on flame spectrometry and direct potentiometry with ion-selective electrodes.

Flow Injection Analysis↗

PubMed1998

Electrolyte disorders and substitution fluid in continuous renal replacement therapy.

Electrolyte balances during acute renal failure treated with continuous convective techniques, such as continuous arteriovenous hemofiltration (CAVH) and its pumped variants, are largely dependent on the eloctrolyte plasma concentration available for ultrafiltration, the ultrafiltration rate and the composition of the replacement solution. As blood sodium concentrations measured by potentiometry (Na +P) and the total ultrafiltrate sodium concentration are very similar, Na +P can be taken as the value of ultrafilterable sodium when choosing the correct sodium concentration in the substitution fluid. In CAVH, the ultrafiltrate contains about 3 m Eq/liter of calcium and 1 m Eq/liter of magnesium that must be replaced by the substitution fluid in order to prevent hypocalcemia and hypomagnesemia. In addition, if plasma potassium levels are normal, 3 to 4 mEq/liter of potassium should be added to the replacement fluid to avoid hypokalemia. Although convection and diffusion are combined in continuous hemodialysis, solute transport is largely mediated by convection; however, the net removal of sodium and calcium is significantly influenced by their concentrations in the dialysate, and the risk of hypomagnesemia and hypokalemia can be attenuated by adjusting magnesium and potassium concentrations in the dialysis solution to levels near to the plasma water values. Since critically ill patients are prone to developing dialysis-induced hypophosphatemia, phosphorous must be monitored and supplemented if necessary, Since CRRT works continuously, serious derangement in fluid and electrolyte homeostasis may occur in the absence of careful prescription and extremely vigilant monitoring.

Acid-Base Equilibrium↗

PubMed1964