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Abstract—Variants of miniplasminogen with an altered primary structure have been designed to study previously described changes in tryptophan fluorescence during plasminogen activation by urokinase. Miniplasminogens that contain the Trp141, Trp215, and Leu217 substitutions (the position of the amino-acid residue is specified by the Chymotrypsin nomenclature) have been tested. The activation of mutants containing a single tryptophan substitution induced changes in the fluorescence spectrum. No changes in the fluorescence spectrum were observed in the case of miniplasminogen containing a double tryptophan substitution. This indicates that both Trp141 and 215 contribute to the fluorescence spectrum shift; however, as suggested previously, the contribution of changes in the Trp215 microenvironment is greater. The Trp141, Trp215, and Leu217 amino-acid substitutions in miniplasminogen have no effect on the rate of plasminogen activation by urokinase. The replacement of the conserved Trp215 residue in serine proteases led to a significant reduction but not loss of the amidolytic activity of plasmin. [ABSTRACT FROM AUTHOR]

Abstract—It has been shown that the curve of the time dependence of tryptophan fluorescence during plasminogen activation by urokinase is well correlated with kinetic curves of activation, which were plotted according to both direct measurements of amidolytic activity of the forming plasmin and the analysis of the plasminogen cleavage products. Three curves represent the intercorrelation within a wide range of the pH and temperature change. We hypothesized that the fluorescence shift is caused by the changes in the Trp215 (Chymotrypsin numbering) side chain environment of activated plasmin. Plasmin activation via proteolytic cleavage of plasminogen induces rotation of the Trp215 side chain with subsequent translocation of the benzene ring of Trp215 from negatively charged (Asp194 and Glu143) to positively charged (Arg175) neighborhood. Our findings show that this rotation is not caused by the indol ring displacement from the substrate recognition pocket, which is provoked by the inhibitor or substrate binding. It has also been demonstrated that the conformation of plasminogen (at least relevant to Trp215 in the substrate recognition pocket) is not sensitive to the pH or temperature changes, while changes in fluorescence spectrum of plasmin correlate with its amidolytic activity. [ABSTRACT FROM AUTHOR]

Complexation in the systems Pd(II)-Cl-HA-HGlu (HA is the l- or d-conformer of 2-methylamino-1-phenylpropanol; HGlu is glutamic acid) was studied using pH-metric titration, electronic absorption spectroscopy, and quantum-chemical modeling. It was found that the ratio of the complex species largely depends on pH and the amine, the crucial factor being stabilization of the structures by hydrogen bonding. This provides explanation to the previous data on the different radioprotective activities of the complexes (HA)[PdCl] containing the l- and d-conformers of the ligand HA. [ABSTRACT FROM AUTHOR]

Chemical equilibria in the heterogeneous system Tb(NO3)3-H2O, physiological saline solutions containing terbium nitrate, and unfractionated heparin ((H4L) Tb(NO3)3-H4L-H2O-NaCl), and solutions containing calcium chloride, terbium nitrate, and unfractionated heparin (CaCl2-Tb(NO3)3-H4L-H2O-NaCl) were studied by mathematical modeling and pH titration. A physicochemical model was designed for two-phase equilibria in the system Tb(NO3)3-H2O, which consists of an aqueous solution and a solid phase of precipitated terbium hydroxide. Formation constants were calculated for terbium hydroxide ions Tb(OH) ( i = 1, 2, 3) in an aqueous phase, and a correlation was found between the amount of precipitated Tb(OH) and pH. The four-component solution Tb(NO3)3-H4L-H2O-NaCl in the range 2.3 ≤ pH ≤ 10.4 is homogeneous; as a result of its investigation, the formation constants were ascertained for significant terbium complexes with heparin: TbL, TbHL, and Tb(OH)2L3−. Chemical equilibria in the five-component solution CaCl2-Tb(NO3)3-H4L-H2O-NaCl were modeled proceeding from the models developed for equilibria in the four-component solution subsystems Tb(NO3)3-H4L-H2O-NaCl and CaCl2-H4L-H2O-NaCl. The modeling showed that the Tb3+ ion is an efficient competitive complex former to the Ca2+ ion, which forms complexes with heparin, and decreases tenfold the concentration of the major complex NaCaL at 6.8 ≤ pH ≤ 7.4 (the pH range of blood plasma stability). [ABSTRACT FROM AUTHOR]

The acid-base properties of unfractionated heparin (H4L) and the complexation of biometal ions (Mg2+ and Ca2+) with heparin in aqueous solutions have been studied by pH titration, using mathematical modeling methods in data processing. The heparin concentration is taken to be equal to the concentration of heparin disaccharide units. The formation constants of the protonated heparin species HiL ( i = 1, 2) have been estimated. The most abundant Mg2+-heparin and Ca2+-heparin complex species have been identified, and their formation constants have been estimated. [ABSTRACT FROM AUTHOR]

The possibility of using an ion-selective electrode containing 1,2-dihydroxyanthraquinone for direct determinations based on complexation reaction in continuous flow analysis was studied. A procedure allows aluminum to be determined in a flow with a throughput of 180 sample/h with a satisfactory precision and accuracy (RSD = 0.84%). [ABSTRACT FROM AUTHOR]

A new method for the computer simulation of chemical equilibria in multicomponent biological liquids has been developed on the basis of a consistent analysis of the databank on equilibria in solutions, combined with the AUTOEQUIL program for the calculation of such equilibria. This method has been applied to the search for new low-molecular-weight endogenous blood anticoagulants with a mechanism of action based on reduction of the equilibrium concentration of biologically active Ca2+ ions by means of complex formation. Using the results of simulation of the metal-ion equilibria in blood plasma with a databank including over 800 units, an adequate model is created, which is capable of describing 64 equilibria in a basis set of 29 components. An analysis of these equilibria revealed four endogenous ligands capable of forming stable complexes with Ca2+, including glutamate (GLU), lactate (LAC), citrate (CIT) and adenosinetriphosphate (ATP). Their anticoagulant properties have been confirmed by universal biological assays in rats in terms of the plasma recalcification time ( RCT) and the activated partial thromboplastin time ( APTT). It has been found that the anticoagulant activities of components are as follows: LAC, 500%; ATP, 240%; GLU, 176%; CIT, 154%(relative to the substrate plasma activity of 100%). [ABSTRACT FROM AUTHOR]

Pd(II) complexes with glutamic acid of the composition K[Pd(HGlu)Cl2] ( I) and [Pd(HGlu)2] ( II) were synthesized and studied by IR and electronic absorption spectroscopy methods. Pd2+–H2O–Cl– and Pd2+–H2O–Cl––H2Glu systems were analyzed by pH-metric titration. The most essential Pd(II) complex forms were established by mathematical modeling and their formation constants were calculated. The electronic absorption spectra of complexes I and II were measured in aqueous and physiological solutions. Complex I was found to be biologically active and to exhibit antimetastatic properties. [ABSTRACT FROM AUTHOR]

Using high-resolution spectrography the authors have investigated the neodymium chloride-malic acid system in aqueous solution at pH 2.0-8.0. They have determined the composition and calculated the stability constants of the complexes NdMal and NdMal. [ABSTRACT FROM AUTHOR]

The stability constants and confidence intervals for monotartrate and ditartrate complexes of the rare-earth elements were determined by the Bjerrum graphical method, using the method of least squares. [ABSTRACT FROM AUTHOR]

Mathematical modelling was used to show the formation of mono and dihydro complexes with glucosamine and the HGl form in physiological solution. The formation constants of these species were calculated. [ABSTRACT FROM AUTHOR]