Alexei L. Margolin

Bio: Alexei L. Margolin is an academic researcher. The author has contributed to research in topics: Polyelectrolyte & Titration. The author has an hindex of 1, co-authored 1 publications receiving 97 citations.

Enzymes in polyelectrolyte complexes. The effect of phase transition on thermal stability.

Abstract: Penicillin amidase, α-chymotrypsin and urease have been immobilized in water-soluble nonstoichiometric polyelectrolyte complexes (N-PEC). N-PEC are formed by modified poly(N-ethyl-4-vinyl-pyridinium bromide) (polycation) and excess poly(methylacrylic acid) (polyanion). N-PEC are a new class of polymers capable, characteristically, of phase transitions solution ⇄ precipitate induced by slight change in pH or ionic strength. Neither the chemical structure of the carrier nor the number of cross-linkages between an enzyme and a carrier change on phase transition. That gives an unique opportunity to elucidate the difference between enzymes immobilized on water-soluble and water-insoluble supports. A detailed study of the phase transition effect on thermal stability of the enzymes and protein-protein interactions has been carried out. The following effects were found. 1 Pronounced thermal stabilization of penicillin amidase and urease may be achieved on two conditions: (a) the enzyme is in the precipitate; (b) the-enzyme is linked to the N-PEC nucleus. Then the thermal stability of N-PEC-bound penicillin amidase increases 7-fold at pH 5.7, 60°C, and 300-fold at pH 3.1, 25°C, compared to the native enzyme. For urease, the thermal stabilization increases 20-fold at pH 5.0, 70°C. 2 The localization of enzyme on N-PEC has been established by titration of α-chymotrypsin bound to a polycation or polyanion with basic pancreatic trypsin inhibitor. Both in solution (pH 6.1) and in N-PEC precipitate (pH 5.7), an α-chymotrypsin molecule bound to a polyanion is fully exposed to the solution. If the enzyme is bound to a polycation, only 20% of α-chymotrypsin molecules in the precipitate and 40% in solution retain their ability for protein-protein interactions. This means that a polycation-bound enzyme is localized in the hydrophobic nucleus of the complex, whereas the polyanion-bound enzyme sits on the hydrophilic shell of the complex. 3 On pH-induced phase transition (pH decreases from 6.1 to 5.7), there occurs a stepwise decrease in penicillin amidase activity which is due to a 9.8-fold increase in the Km for 2-nitro-4-phenylacetamidobenzoic acid. 4 Change of the catalytic activity and thermal stability of N-PEC-bound penicillin amidase is fully reversible and reproducible. Such soluble-insoluble immobilized enzymes with controllable thermal stability and activity may be used for simulating events in vivo and in biotechnology.

Enzyme Multilayers on Colloid Particles: Assembly, Stability, and Enzymatic Activity

Abstract: Colloidal biocatalysts, comprising polystyrene (PS) carrier particles coated with enzyme multilayers, were fabricated via the layer-by-layer self-assembly method. Glucose oxidase (GOD), horseradish peroxidase (POD), or preformed enzyme−polyelectrolyte complexes were assembled in alternation with oppositely charged polyelectrolytes onto PS particles. Microelectrophoresis, single-particle light scattering, and transmission electron microscopy confirmed stepwise growth of the multilayer films on the colloid particles. The high surface area enzyme multilayer-coated particles were successfully employed as specific enzyme reactors (i.e., as catalysts). Whereas no loss in activity was observed for the enzymes immobilized directly onto particle surfaces, precomplexing the enzymes with polymer in solution drastically reduced their activity (by up to 70%). The enzymatic activity (per particle) was found to increase with the number of enzyme layers immobilized, irrespective of whether the enzyme was precomplexed. Ho...

Sodium carboxymethylcellulose-CTAB interaction: a detailed thermodynamic study of polymer-surfactant interaction with opposite charges.

Abstract: Interaction between polymer and surfactant bearing opposite charges is much more complex from a physicochemical point of view as compared to interaction between ionic surfactant and nonionic polymer. Electrostatic and hydrophobic interactions interplay in the former, whereas the hydrophobic effect is the prevailing factor in the latter. We have studied the interaction between a water-soluble polyanion, sodium salt of carboxymethylcellulose (NaCMC), with a cationic amphiphile, CTAB, in aqueous medium. There were manifold discrepancies with the reported works in NaCMC-alkyltrimethylammonium bromide, which is assumed to be an effect of difference in degree of substitution, which in turn affects the charge density of the polymer chain. We have noticed that the bulk complexation and interfacial interaction driven by electrostatic forces operate side by side. Thereafter, there is a wrapping process by the polyanion to the polymer-induced smaller surfactant aggregates driven by increase in entropy of the solution as a result of expulsion of the counterions from the ionic atmosphere around the surfactant aggregate. Because of the electrostatic interaction, hydrophobicity of the polymer-surfactant complex increases, leading to coacervation, and again solubilization in the hydrophobic core of the self-aggregated structure provided by the added excess CTAB. The tensiometric, conductometric, microcalorimetric, and turbidimetric techniques have been applied to address these problems.

Roles of Electrostatic Interaction and Polymer Structure in the Binding of β-Lactoglobulin to Anionic Polyelectrolytes: Measurement of Binding Constants by Frontal Analysis Continuous Capillary Electrophoresis

Abstract: Frontal analysis continuous capillary electrophoresis was used to measure the binding of β-lactoglobulin (BLG) to sodium poly(styrenesulfonate) (PSS) and sodium poly(2-acrylamido-2-methylpropanesulfonate) (PAMPS), two strong polyanions with similar linear charge densities. The binding isotherms obtained were well-fit by the McGhee−von Hippel equation, yielding the intrinsic binding constant, Kobs, and the binding site size, n, representing the number of polymer segments per bound protein. Two opposite ionic strength (I) dependencies of Kobs for BLG−PSS were found depending upon pH, that is, increase of Kobs with I at pH 7.0, and decrease of Kobs with I at pH 6.3. The opposite I dependencies reflected the roles of electrostatic interactions for systems with heterogeneously charged components, but also demonstrated the inapplicability of a simple formulation (log Kobs = log K° − Zφ log [M+]) put forward for the binding of protein to DNA. Kobs for PAMPS was always much smaller than that for PSS at equal pH. ...