Preparation of giant liposomes in physiological conditions and their characterization under an optical microscope.

Unilamellar liposomes with diameters of 25-100 microns were prepared in various physiological salt solutions, e.g., 100 mM KCl plus 1 mM CaCl2. Successful preparation of the giant liposomes at high ionic strengths required the inclusion of 10-20% of a charged lipid, such as phosphatidylglycerol, phosphatidylserine, phosphatidic acid, or cardiolipin, in phosphatidylcholine or phosphatidylethanolamine. Three criteria were employed to identify unilamellar liposomes, yielding consistent results. Under a phase-contrast microscope those liposomes that showed the thinnest contour and had a vigorously undulating membrane were judged unilamellar. When liposomes were stained with the lipophilic fluorescent dye octadecyl rhodamine B, fluorescence intensities of the membrane of individual liposomes were integer multiples (up to four) of the lowest ones, the least fluorescent liposomes being those also judged unilamellar in the phase-contrast image. Micropipette aspiration test showed that the liposomes judged unilamellar in phase and fluorescence images had an area elastic modulus of approximately 160 dyn/cm, in agreement with literature values. The giant liposomes were stable and retained a concentration gradient of K+ across the membrane, as evidenced in fluorescence images of the K(+)-indicator PBFI encapsulated in the liposomes. Ionophore-induced K+ transport and associated volume change were observed in individual liposomes.     

Synthesis of conjugates of bovine serum albumin with water-soluble ytterbium porphyrins

The ytterbium complex of 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin was synthesized as an IR-fluorescent label and covalently bound to bovine serum albumin. The resulting conjugate fluoresces at 985 nm and is of interest for use in IR-fluorescent tumor diagnostic, immunoassay, and energy transfer studies. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 1; see also http://www.maik.ru.     

Preparation and characterization of bovine albumin isoforms

Albumin undergoes changes in conformation and isomerizations by disulfide interchange of unknown biological significance. The aim of this study was to prepare and characterize albumin isoforms, which were stable under near physiological conditions. Modified albumins were obtained by urea denaturation and renaturation, and by aging at low ionic strength and alkaline pH in the presence of cysteine. We describe a cathodic electrophoresis technique, which allows the separation of albumin isoforms with greater positive charge. Differences between native and modified albumins were analyzed by new criteria based on the reactivity of the thiol and histidyl residues and on the susceptibility of the disulfide bonds to sulfitolysis. Modified albumins had, (i) a more cationic component which disappears by sulfitolysis of the disulfide bonds or by incubation with a glutathione redox system; (ii) higher reactivities of the free thiol group and of the histidyl residues, and; (iii) decreased fluorescence. These differences were not observed when processes were carried out on albumin with the thiol group blocked by iodacetic acid, but reappeared with the addition of cysteine. Renatured and aged albumins differed in the nature of the cationic component. Generation of albumin isoforms is dependent on the presence of a free thiol group and seems to involve thiol disulfide interchanges.     

Preparation and partial characterization of iron-sulfur, iron-selenium, and iron-tellurium complexes of bovine serum albumin.

An artificial Fe-S* protein was prepared by the reaction of bovine serum albumin with FeSO4 and Na2S or with a synthetic Fe-S*-1,4-butanenedithiol complex. These improved methods enabled us to characterize the derivatives from serum albumin. The Fe-S* albumin complex has about 20 iron ions and 14 labile sulfur atoms per molecule of the protein, whose absorption spectrum closely resembled that of 2Fe-2S* proteins. Its electron paramagnetic resonance spectrum exhibited signals different from those of ferredoxins. The addition of p-chloromercuriphenylsulfonate quenched the optical absorption in the visible region as well as the electron paramagnetic resonance signals. These properties of the albumin-iron complex are similar to those of iron-sulfur dithiothreitol and mercaptoethanol complexes, suggesting that the albumin-iron complex has one or more protein ligands besides sulfur lignads. Presumably, the oxygen atom of the tyrosine residue, or other hydroxyamino acids participates in the complex formation. In this context, the albumin polypeptide appears to be incapable of forming an iron-sulfur cluster identical to those of ferredoxins. Yet, from the albumin-iron derivative, the extrusion of the iron-sulfur core with benzenethiol provided products similar to those from ferredoxins. The iron-selenium and iron-tellurium derivatives of the bovine serum albumin were prepared and partially characterized by optical absorption and electron paramagnetic resonsnace spectroscopies. These results imply that both selenium and tellurium can be incorporated into the protein molecule as the respective labile components.     

Immunocorrection of the physiologic status of white rats by sidnofen conjugates with bovine serum albumin

The effect of immunisation by covalent conjugates of known psychostimulant and antidepressant sydnophen with bovine serum albumin (BSA) on behaviour, formation of conditioned reflex reactions and alcoholization of white rats has been studied. The immunization of sydnophen with BSA by conjugates permits to obtain a long-term alteration of the emotional status: suppression of behavioral activity, learning and alcohol attraction of rats similar in some elements to the action of neuroleptic drugs. The direction of these alterations is opposite to ones caused by the action of sydnophen. It gives possibility to consider fruitful the conception on the ways of long-term immunocorrection of the physiological status of organism.     

Chemical modification of proteins under high pressure. Preparation of ferrocene-attached bovine serum albumin and glucose oxidase.

High hydraulic pressure was used for denaturing proteins during chemical modifications. Bovine serum albumin and glucose oxidase were selected as the first targets of this unique technique and the ferrocene group was introduced into them, to obtain a macromolecular electron mediator and a self-electron-mediating oxidase, respectively. The result was compared with those obtained under non-denaturing conditions and under urea-denatured conditions. As for the number of ferrocene group linked to the protein, the pressure denaturation is superior to chemical denaturants, where ferrocenecarboxyaldehyde was used as the modifier. In both proteins the ferrocene group seemed to be introduced mainly inside the molecules with the pressure method, as the native conformation of the protein was restored when the high pressure was removed.     

Steroid-bovine serum albumin conjugates: molecular characterization and their interaction with androgen and estrogen receptors

Conjugates of testosterone-3-carboxymethyloxime (T-3-CMO), testosterone-17-hemisuccinate (T-17-HS), 17 beta-estradiol-6-carboxymethyloxime (E-6-CMO), or 17 beta-estradiol-17-hemisuccinate (E-17-HS) and bovine serum albumin (BSA) with varying steroid:protein ratios were prepared using the mixed anhydride method. Dialysis followed by molecular filtration yielded monomer steroid-BSA conjugates with a molecular weight of 70,000 dalton, and polymer conjugates with molecular weights of 140,000 dalton and higher. When conjugates were prepared with increasing initial steroid:BSA molar ratios the ratio of the obtained conjugates increased, in parallel with a decrease in the relative amount of monomers and an increase in the mean molecular size of polymers. The molecular properties of these conjugates were studied further by polyacrylamide gel electrophoresis (PAGE) in native and denaturing conditions. In native PAGE the monomer fractions showed one main band with a mobility slightly lower than BSA and a faint band corresponding with BSA-dimers. The polymer fractions consisted of a heterogeneous population of protein oligomers with molecular weights varying from 140,000 to over a million dalton. In the presence of sodium dodecylsulphate part of the polymers dissociated into monomers. In buffered aqueous solutions the bulk of the conjugate preparation retained its molecular size and composition, although the generated covalent bonds were found to be liable to spontaneous hydrolysis. Steroid-protein conjugates were shown to contain appreciable amounts of non protein-bound steroids. Binding of T-BSA to androgen receptors in rat ventral prostate cytosol was assayed using LH-20 chromatography and sucrose gradient centrifugation analysis. Binding of E-BSA to estrogen receptors was analysed with rat uterus cytosol using the dextran coated charcoal assay and the sucrose gradient centrifugation technique. Relative binding affinities (RBA) were analyzed in competition experiments using radiolabeled ligands. It was found that the molecular size of the conjugate does not influence its interaction with steroid receptors. Steroid coupled via the 17-position show a higher RBA to receptors than the T-3 or E-6 derivatives. The RBA of T-3-BSA, T-3-CMO, T-17-BSA and T-17-HS appeared to be very low, i.e. between 0.1 and 1.7% of the RBA of dihydrotestosterone. Consequently, high concentrations of conjugate are required to saturate androgen receptor binding sites. Under these conditions involvement of type II and eventually type III binding sites, which show less ligand specificity and lower affinity, may be anticipated preventing exclusive detection of androgen receptors.(ABSTRACT TRUNCATED AT 400 WORDS)     

Non-enzymatic deamidation and autofragmentation of lysozyme and albumin under physiological conditions

Nonenzymic deamidation of amides in proteins (lysozyme and albumin) under conditions which imitate physiological ones has been experimentally established with subsequent asparagine-dependent autofragmentation of the polypeptide chain.     

The acylation of bovine serum albumin with diacetylcycloserine.

The reaction of the amino groups of bovine serum albumin (BSA) with diacetylcycloserine (I) at pH 7.2-9.0 proceeded with both acylation by the diacetyl-beta-aminooxy-D-alanyl (DAA) group and acetylation. The number of DAA groups was determined by their conversion to cycloserine (III) which can be accurately measured in micromolar amounts. The method was developed using the model compound diacetyl-beta-aminooxy-D-alanine butyl amide (II) which was converted to beta-aminooxy-D-alanine butyl amide (IV) by methanolysis and then to cycloserine by basic ring-closure of IV. Calculations using results obtained by this method combined with the experimentally determined number of free amino groups in the modified BSA indicated that the reaction of excess I with BSA effected the acetylation of about 35 and the acylation with DAA groups of about 22 of the 59 amino groups. These findings were supported by experiments demonstrating that the amount of acetic acid formed by hydrolysis of the modified BSA was approximately that predicted from the results of the cycloserine analyses.     

Spectroscopic exploration and thermodynamic characterization of desvenlafaxine interacting with fluorescent bovine serum albumin

The mechanism of the interaction between bovine serum albumin (BSA) and desvenlafaxine was studied using fluorescence, ultraviolet absorption, 3‐dimensional fluorescence spectroscopy, circular dichroism, synchronous fluorescence spectroscopy, cyclic voltametry, differential scanning calorimetry, and attenuated total reflection–Fourier transform infrared spectroscopic techniques under physiological condition at pH 7.4. Stern‐Volmer calculations authenticate the fluorescence of BSA that was quenched by desvenlafaxine in a collision quenching mode. The fluorescence quenching method was used to evaluate number of binding sites “n” and binding constant K _A that were measured, and various thermodynamic parameters were evaluated at different temperatures by using the van't Hoff equation and differential scanning calorimetry technique, which indicated a spontaneous and hydrophobic interaction between BSA and desvenlafaxine. According to the Förster theory we calculate the distance between the donor, BSA and acceptor, desvenlafaxine molecules. Furthermore, circular dichroism and attenuated total reflection–Fourier transform infrared spectroscopy indicate nominal changes in the secondary structure of the protein.     

Optimization and validation of analytical conditions for bovine serum albumin using capillary electrophoresis.

A quick and reproducible capillary electrophoresis method was optimized and validated for the assay of bovine serum albumin (BSA). The effects of various parameters such as pH of buffer, concentration of buffer, capillary dimensions, use of coated capillaries, and additives such as surfactants and protein solubilizers were evaluated. The capillary coatings or additives did not give any advantage in reducing the surface adsorption of BSA on the capillary walls. The optimized conditions include use of borate buffer, pH 8.5 having a concentration of 150 mM in a 27 cm capillary with an aperture window of 100 x 200 microns for detection. The optimized method for the detection of BSA was validated. The interday and intraday coefficient of variation was not greater than 7.59% at BSA concentrations of 25-1000 micrograms/ml. The method developed was reproducible and accurate.     

Preparation and in vitro photodynamic activities of novel axially substituted silicon (IV) phthalocyanines and their bovine serum albumin conjugates

Two novel axially substituted phthalocyanines, namely bis(4-(4-acetylpiperazine)phenoxy)phthalocyaninatosilicon (IV) (1) and its N-methylated derivative 2, have been synthesized. The dicationic phthalocyanine 2 is non-aggregated in water and exhibits good photophysical properties. The non-covalent BSA conjugates of these compounds have also been prepared. Compound 2 and the conjugate 2-BSA show extremely high photodynamic activities toward B16 melanoma cancer cell lines. The corresponding 50% growth-inhibitory (IC50) ratios are 33 and 38 nM, respectively.