Polyelectrolyte complexes of lactoferrin and pH-sensitive microparticles on their basis

Suspensions of insoluble polyelectrolyte complexes of dextran sulfate (DS) of different molecular masses with lactoferrin (LF) have been fabricated and characterized. The encapsulation efficiency of LF and DS in a complex at pH 3.0 and 4.0 was assessed, and particles were characterized by their sizes and ζ-potential. The complexes formed at pH 3.0 differed by a higher stability level. The interaction with DS resulted in a twofold decrease in the antioxidant activity of LF, although the formation of complexes was not accompanied by conformational changes in LF molecules according to IR-spectrometry data. Microencapsulation was carried out by treating the suspensions with negatively charged LF-DS complexes with protamine and chitosane solutions with different molecular masses. The composition, size, and the ζ-potential of interaction products were assessed which allowed us to select the conditions for the preparation of pH-sensitive polyelectrolyte microparticles loaded with LF which would be able to gradually release glycoprotein under conditions that model the passage through the gastrointestinal tract of humans. These data indicate that this approach is promising for the creation of pH-sensitive biopolyelectrolytes suitable for oral administration of LF to target cells.     

Incapsulation of enzymes into polyelectrolyte nano- and microcapsules and the problem of the development of enzymatic microdiagnostics

The incapsulation of proteins into polyelectrolyte microcapsules (PE-microcapsules) has been studied with the aim to develop microdiagnostica for the presence of low-molecular-weight compounds in native biological fluids. The problem was solved using two enzymes: lactate dehydrogenase and urease. Polyelectrolyte microcapsules were prepared using two polyanions: polystyrene sulfonate (PSS) and dextran sulfate (DS), and two polycations: polyallylamine (PAA) and polydiallylmethylammonium (PDADMA). CaCO3 microspherulites with the incapsulated enzyme served as a "core" in the formation of polyelectrolyte microcapsules. It was shown that the main problem in the preparation of a polyelectrolyte microdiagnosticum is the selection of an oppositely charged pair of polyelectrolytes optimal for the active functioning of the enzyme. It follows from the results obtained that the best polyelectrolyte pairs for the formation of the envelope of a PE-microcapsule are PAA/DS and PAA/PSS for lactate dehydrogenase and PSS/PDADMA for urease. Taking into account these data, we designed enzyme-containing microcapsules with different polyelectrolyte compositions and different numbers of layers and studied their properties.     

Enzyme-polyelectrolyte complexes in water-ethanol mixtures: negatively charged groups artificially introduced into alpha-chymotrypsin provide additional activation and stabilization effects

Formation of noncovalent complexes between alpha-chymotrypsin (CT) and a polyelectrolyte, polybrene (PB), has been shown to produce two major effects on enzymatic reactions in binary mixtures of polar organic cosolvents with water. (i) At moderate concentrations of organic cosolvents (10% to 30% v/v), enzymatic activity of CT is higher than in aqueous solutions, and this activation effect is more significant for CT in complex with PB (5- to 7-fold) than for free enzyme (1.5- to 2.5-fold). (ii) The range of cosolvent concentrations that the enzyme tolerates without complete loss of catalytic activity is much broader. For enhancement of enzyme stability in the complex with the polycation, the number of negatively charged groups in the protein has been artificially increased by using chemical modification with pyromellitic and succinic anhydrides. Additional activation effect at moderate concentrations of ethanol and enhanced resistance of the enzyme toward inactivation at high concentrations of the organic solvent have been observed for the modified preparations of CT in the complex with PB as compared with an analogous complex of the native enzyme. Structural changes behind alterations in enzyme activity in water-ethanol mixtures have been studied by the method of circular dichroism (CD). Protein conformation of all CT preparations has not changed significantly up to 30% v/v of ethanol where activation effects in enzymatic catalysis were most pronounced. At higher concentrations of ethanol, structural changes in the protein have been observed for different forms of CT that were well correlated with a decrease in enzymatic activity. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 267-277, 1997.     

Interaction of invertase with polyelectrolytes

In connection with our work on polyelectrolyte complex formation with polyampholytes, the interaction between invertase and several linear polyelectorlytes has been investigated by means of turbidimetry, light scattering measurements, and determination of the enzyme activity. Polyelectrolyte complex formation of invertase was shown to occur with cationic polyelectrolytes only. The light-scattering data yield information on aggregation and desegregation processes in complex formation. As indicated by our results, only a part of the protein molecules is engaged in this Coulombic interaction, and this part shows a rather small enzyme activity only. Thus, a direct interaction between invertase and a cationic polyelectrolyte is no effective approach to enzyme binding, but a complete immobilization of invertase can be achieved via an "inclusion flocculation" with a symplex formed by interaction between an anionic and a cationic linear polyelectrolyte or via immobilization in symplex microcapsules.     

Cationic polyelectrolytes-lipases complexes formation as tool for recovery of these enzymes from their natural sources

In the present paper the formation of complexes between positively charge polyelectrolyte (polyethyleneimine and chitosan) and Candida rugosa lipase from a crude extract and porcine lipase from pancreas commercial homogenate preparations were analyzed. The solubility of lipases-cationic polyelectrolytes formation was dependent on: polyelectrolyte densities electrical charge, polyelectrolyte and enzyme concentrations and salts present in the solution. The lipase was recovered from the non-soluble complex by adding of NaCl at a given pH. Although the polyelectrolytes did not affect lipase biological activity, both of them produced good enzyme recovery (>90%); however, purification factors were low. This methodology appears to be a good previous prepurification and concentration method, using, low-cost polymers, allows the design of a purification method where the protein of interest is present in a large volume with respect to the small amount of polyelectrolyte added.     

Interaction of intracellular RNAase from Aspergillus clavatus with derivatives of its substrates]

Using spectrophotometric and kinetic methods and also the methods of protection of Aspergillus clavatus RNAse (EC 3.1.4.23) by adenine nucleotides and their components against inactivation by means of acylation or heating, it was found that RNAse-nucleotide complex was formed by association of one enzyme molecule with one nucleotide molecule. It was also shown that all components of nucleotides (base, ribose and phosphate) take part in the formation of such complex and the removal of one of them (base or phosphate) lead to loosening of bindings of remaining fragments (ribose-5'-monophosphate, adenine) with the active site of RNAse, and to disappearance of bends within the pH range of 3.0-4.0 on the plot of pKi (5'-MP) versus pH, within the pH range of 5.5-7.0 on the plot of oKi (Ado) versus pH. The possibility of participation of associative pair RNAse imidasole groups - nucleotide phosphate groups and RNAse carboxylic group - nucleotide base in the mechanism of formation of enzyme-nucleotide (enzyme-substrate) complexes is postulated.     

Platform design for extraction and isolation of Bromelain: Complex formation and precipitation with carrageenan

The main objective of this work was to investigate for the first time the molecular mechanism of complex formation between bromelain (a positively charged enzyme) and carrageenan (a natural strong polyelectrolyte, negatively charged) using spectroscopy techniques and thermodynamic approaches. The Bromelain-Carrageenan complex showed a maximal non-solubility at pH around 5.1. The solubility was dependent on pH and ionic strength of the medium. To re-dissolve the formed complex, the pH was changed and 500 mM of NaCl was added to the initial solution, proving the columbic mechanism for the formation of non-soluble complex. The formation of the carrageenan-bromelain complex increased in 8 °C the enzyme thermal stability, while its biological activity was not modified. The amount of total enzyme recovered in solution after precipitation with around 0.08% w/v of carrageenan was 85–90%.     

Co-immobilization of dextransucrase and dextranase for the facilitated synthesis of isomalto-oligosaccharides: Preparation, characterization and modeling

Co-Immobilization of dextransucrase (DS) and dextranase (DN) into calcium alginate includes the co-entrapment of soluble DS and adsorbed DN. DS converts sucrose into dextran, which is the substrate for DN, so that isomalto-oligosaccharides (IMOs) are follow-up products of dextran hydrolysis. The boundary conditions for the successful preparation are investigated with respect to choice of DN adsorbate, surface modifications using blotting agents and optimal enzyme activity ratios. Further, repetitive batch experiments suggest the selection of medium activity ratios for continuous use (0.3 U(DN)U(-1) (DS), e.g.). Product formation at various cosubstrate:substrate concentrations as well as at different DN:DS ratios are discussed. Moreover, the complexity of the bi-enzymatic system can be reduced considering the molar ratios of cosubstrate:substrate (glucose:sucrose). Based on these factors, a mechanistic kinetic model is developed, which distinguishes the corresponding contributions of the two enzymes upon overall product formation. In general, at low glucose:sucrose ratios isomaltose synthesis is featured primarily by DN action. Yet with increasing amounts of glucose both the quantity and quality of DN substrate changes, so that its contribution to product formation decreases in an exponential manner; still the overall product yield continuously increases due to enhanced DS contribution.     

A spectrophotometric study of Penicillium brevicompactum RNAase complex formation with adenine nucleotides]

Spectrophotometric study of extracellular Pen. brevicompactum RNAse interaction with adenyl nucleotides and constituents have been carried out. It is states that: 1) complex RNAse--nucleotide is formed by association of one enzyme molecule with one nucleotide molecule; 2) all the nucleotide components base sugar and phosphate, take part in the formation of this complex; 3) for the effective association of this complex it is necessary to have a high correspondence (complementaryty) of nucleotide geometric configuration to the space composition of the active site of RNAse.     

Cytomorphologic assessment of the effect of Bacillus intermedius RNase on the organs of experimental animals]

Cytomorphological changes in the organs of laboratory animals after their treatment with RNAse from Bacillus intermedius were investigated. It was shown that the effect of RNAse on the thymus and spleen was evident from stimulation of the elements of the lympho and hemopoiesis while its effect on the liver manifested itself in increased stromal response of the liver and higher functional activity of the organ. The observed effects did not depend on catalytic activity of the enzyme.     

The histological evaluation of the effect of Bacillus intermedius RNAse on the organs of immunogenesis in laboratory animals]

Histological changes in organs of immunogenesis of experimental animals after RNAse Bacillus intermedius treatment have been studied. The effect of RNAse on organs is revealed in activation of both cell and humoral immunity and factors of nonspecific resistance at early stage of reaction. The inhibition of immunological reactions and factors of nonspecific resistance takes place at later stages of enzyme action. The caused effects don't depend on catalytic enzyme activity.     

Dermatan sulfate as a stabilizer for protein stability in poly(lactide-co-glycolide) depot

Dermatan sulfate (DS), a glycosaminoglycan family, was investigated as a additive to enhance the stability of therapeutic protein with low p/ value loaded in poly(lactide-co-glycolide) (PLGA) microspheres prepared by water-in-oil-in-water (W₁/O/W₂) method. DS maintains negative charge below pH 3.0 because of its sulfate groups, while most anionic polymer with carboxyl groups becomes neutral charge at that pH. Thus, at pH 3.0 DS can form a polyelectrolyte complex with a protein with lower p/ such as exendin-4, insulin, and human growth hormone. In order to complex with DS, bovine serum albumin (BSA) was employed as a model protein, which has low p/value (p/= 4.8). The complex prepared at pH 3.0 showed a nano-size in the range of 100∼200 nm with a mono distribution. During the preparation of PLGA depot, DS concentration in water phase increases with decreasing the formation of non-covalent BSA aggregates and enhancing BSA loading efficiency. It means that DS/BSA complex system enabled to keep a stability of BSA at the water/organic interface. In an in vitro BSA release test, PLGA depot with DS exhibited a lower initial burst kinetic than only PLGA depot and continuous BSA release in almost 100% for 23 days. From the results, it was concluded that DS as an additive in PLGA depot, has a potential for the long-term delivery of therapeutic proteins with lower p/ value.     

Structural studies of Saccharomyces cerevesiae mitochondrial NADP-dependent isocitrate dehydrogenase in different enzymatic states reveal substantial conformational changes during the catalytic reaction

Isocitrate dehydrogenases (IDHs) catalyze oxidative decarboxylation of isocitrate (ICT) into alpha-ketoglutarate (AKG). We report here the crystal structures of Saccharomyces cerevesiae mitochondrial NADP-IDH Idp1p in binary complexes with coenzyme NADP, or substrate ICT, or product AKG, and in a quaternary complex with NADPH, AKG, and Ca(2+), which represent different enzymatic states during the catalytic reaction. Analyses of these structures identify key residues involved in the binding of these ligands. Comparisons among these structures and with the previously reported structures of other NADP-IDHs reveal that eukaryotic NADP-IDHs undergo substantial conformational changes during the catalytic reaction. Binding or release of the ligands can cause significant conformational changes of the structural elements composing the active site, leading to rotation of the large domain relative to the small and clasp domains along two hinge regions (residues 118-124 and residues 284-287) while maintaining the integrity of its secondary structural elements, and thus, formation of at least three distinct overall conformations. Specifically, the enzyme adopts an open conformation when bound to NADP, a quasi-closed conformation when bound to ICT or AKG, and a fully closed conformation when bound to NADP, ICT, and Ca(2+) in the pseudo-Michaelis complex or with NADPH, AKG, and Ca(2+) in the product state. The conformational changes of eukaryotic NADP-IDHs are quite different from those of Escherichia coli NADP-IDH, for which significant conformational changes are observed only between two forms of the apo enzyme, suggesting that the catalytic mechanism of eukaryotic NADP-IDHs is more complex than that of EcIDH, and involves more fine-tuned conformational changes.     

Conjugated polyelectrolytes: conformation-sensitive optical probes for detection of amyloid fibril formation

The in vivo deposition of amyloid fibrils is a hallmark of many devastating diseases known as the amyloidoses. Amyloid formation in vitro may also complicate production of proteins in the biotechnology industry. Simple, sensitive, and versatile tools that detect the fibrillar conformation of amyloidogenic proteins are thus of great importance. We have developed a negatively charged conjugated polyelectrolyte that displays different characteristic optical changes, detected visually or by absorption and emission, depending on whether the protein with which it forms a complex is in its native state or amyloid fibril conformation. This simple, rapid, and novel methodology was applied here to two amyloidogenic proteins, insulin and lysozyme, and its validity for detection of their fibrillar conformation was verified by currently used methods such as circular dichroism, transmission electron microscopy, and Congo red absorption.     

Myofibrillar creatine kinase activity inferred from a 3D model

Myofibrillar creatine kinase (CK) that buffers ATP during fluctuating muscle energy metabolism has been selected for studies of conformational changes underlying the cellular control of enzyme activity. The force field was computed for three energetic states, namely for the substrate-free CK molecule, for the molecule conjugated with the MgATP complex, and for the molecule conjugated with the pair of reactants MgATP-creatine. Without its substrates, the enzyme molecule assumes an inactive "open" form. Upon binding of the MgATP complex, the CK molecule takes up a reactive "closed" conformation. Subsequent binding of creatine yields a nonreactive "intermediary" conformation. Acid-base catalysis is considered to be the basic principle for the reversible transfer of the phosphoryl group between the substrates. The results indicate that the substrate-induced energy minimizing conformational changes do not represent a sufficient condition for CK activity and that some other essential component of physiological control at the cellular level is involved in the transition from the intermediary to the closed structure of the molecule.     

Effect of alpha2 macroglobulin on some kinetic parameters of trypsin.

1. Complex formation of trypsin with alpha2 macroglobulin results in marked changes of the Michaelis-Menten constant, pH optimum and sensitivity to ionic strength in a system using N-carbobenzoxy-glycylglycyl-L-arginine-2-naphthylamide as substrate. 2. In contrasts to the inhibition (50%) observed when alpha2 macroglobulin-bound trypsin is assayed under conditions optimal for the free enzyme, there is minimal reduction of activity when determinations are performed at a substrate concentration and pH optimal for the bound enzyme. 3. The changes in substrate concentration and ionic environment required for maximum activity of alpha2 macroglobulin-bound trypsin are similar to those observed with enzymes embedded in polyelectrolyte matrices and may reflect alterations in the microenvironment of the enzyme resulting from conformational changes of the macromolecule during interaction with trypsin. 4. Enzymatic activity of trypsin towards casein is greatly reduced by alpha2 macroglobulin, even under assay conditions optimal for the bound enzyme, confirming previous findings that access to the active center for high-molecular weight substrates is sterically hindered by alpha2 macroglobulin.     

Multiple effects of chemical reagent on enzyme: o-phthalaldehyde-induced inactivation,dissociation and partial unfolding of lactate dehydrogenase from pig heart

The effects of o-phthalaldehyde (OPTA) on lactate dehydrogenase (LDH) have been studied by following changes in enzymatic activity, aggregation state and conformation. Treatment with OPTA resulted in pseudo first-order inactivation of LDH over a wide concentration range of the inhibitor, and the second-order rate constant was estimated to be 1.52 M⁻¹ s⁻¹. The loss of enzyme activity was concomitant with the increases in absorbance at 337 nm and fluorescence intensity at 405 nm. Complete loss of enzyme activity was accompanied by the formation of approximately 4 mol isoindole derivatives per mole LDH subunit. Cross-linking experiments verified enzyme dissociation during OPTA modification, which could be attributed to the modification of both thiol groups and lysine residues. Circular dichroism (CD) spectra showed that the secondary structure of the OPTA-modified enzyme decreased correspondingly. Comparison of the inactivation with the conformational changes of the enzyme suggests that the active site of the enzyme exhibits greater conformational flexibility than the enzyme molecule as a whole. It is concluded that OPTA modification has multiple effects on LDH, including its inactivation, dissociation and partial unfolding.     

Lactate dehydrogenase in an interpolyelectrolyte complex. Function and stability

A new method for encapsulating enzymes by multilayer polyelectrolyte coating is proposed. The method consists in a stepwise adsorption of polyelectrolytes from solution onto protein aggregates formed by salting out the proteins in highly concentrated salt solutions. Polystyrene sulfonate and fluorescence-labeled polyalylamine were used for capsule formation. The size of lactate dehydrogenase aggregates covered by four layer pairs of electrolytes was 1-5 microns, as indicated by fluorescence microscopy. The catalytic characteristics and stability of pig muscle lactate dehydrogenase (EC 1.1.1.13) incapsulated in multilayer electrolyte complex obtained by this method were studied. It was found that the affinity of the substrate pyruvate for the enzyme in the polyelectrolyte complex (K(M)) did not essentially change as compared with the free enzyme. Incapsulated lactate dehydrogenase showed the following features that distinguish it from the free form: (1) the lifetime in diluted solutions increases from 30 min (without capsules) to 1-2 days (in capsules); (2) a higher stability to basic denaturation (up to pH 10); and (3) the absence of substrate inhibition of enzyme in the polyelectrolyte complex. The changes in the catalytic characteristics of incapsulated lactate dehydrogenase are discussed in terms of an increase in effective pK values of amino acid perturbed by polyelectrolyte coating of enzyme.     

PAR对氨基酰化酶不可逆抑制动力学研究

本文将邹氏的在酶的活性修饰剂存在下的底物反应动力学理论应用于氨基酰化酶被金属螯合剂PAR脱锌而失活的动力学研究。通过对不同浓度的PAR存在下底物反应过程和含有PAR的不同浓度的底物中酶促反应的分析,讨论了PAR对氨基酰化酶的脱锌机制。这一过程很可能按如下机制进行:首先,PAR与酶分子活性部位的锌结合,形成一复合物,这一步是较快的反应,然后发生一个可逆的构象变化,最后是不可逆的去锌步骤。锌的存在显然稳定了酶活性部位的构象,而这正是酶活性所必需的。     

Molecular dynamics simulation of polyelectrolyte with oppositely charged monomeric and dimeric surfactants

Interactions of anionic polyelectrolyte (PE) with cationic monomeric (MS) and dimeric surfactants (DS) have been investigated by coarse-grained molecular dynamics (MD) simulation. A PE/surfactant mixture is observed to evolve over time into micellar complex of increasing size. The critical aggregation concentration (CAC) is qualitatively found to be much lower than the critical micellization concentration (CMC) of the free surfactant. Compared to the monomeric analog, a DS interacts more strongly with the oppositely charged polyion chain. The equilibrium complex size becomes larger with increasing surfactant concentration. Simulation results are consistent with experimental observations and reveal that the electrostatic and hydrophobic interactions play an important role in the formation of micellar complex.