Functional immobilized biocatalysts

Stable and Prolonged Autonomous Oscillation in a Self-Oscillating Polymer Brush Prepared on a Porous Glass Substrate

We developed an autonomous functional surface, named a "self-oscillating polymer brush surface", which exhibits swelling-deswelling of the modified polymer chains synchronized with the Belousov-Zhabotinsky (BZ) reaction. The grafted polymer chain is a random copolymer composed of thermoresponsive N-isopropylacrylamide, N-(3-aminopropyl)methacrylamide, and ruthenium tris(2,2'-bipyridine) [Ru(bpy)₃]. To provide stable oscillations over a long period of time, suppression of the dilution of the BZ reactants inside the polymer surface and the increase in the amount of immobilized Ru(bpy)₃ are important. Here, we modified the self-oscillating polymer brush on a porous glass substrate and characterized its dynamic behavior. The increased surface area of the porous glass allowed for an efficient introduction of the metal catalyst, which resulted in a stable BZ reaction observable by optical microscopy. Compared with an aqueous BZ solution and the self-oscillating polymer modified on a glass coverslip, the wave velocity and diffusion coefficient were significantly lower for the porous glass system, which suggested that the reaction-diffusion of the reactants was markedly different than those of the other two systems. Moreover, the wave velocity was unchanged on the porous glass system for 1 h, whereas that of the solution dropped by 30 μm s^-1. Waveform analyses based on the Field-Körös-Noyes mechanism revealed that densely packed Ru(bpy)₃ in the porous glass system affects the duration of the key processes in the BZ reaction. These findings can help with understanding the dynamic behavior of the self-oscillating polymer brush on a porous glass substrate. Stable self-oscillations on the polymer brush-grafted porous glass substrate will aid future applications such as mass transport systems.

Polycation-globular protein complex: Ionic strength and chain length effects on the structure and properties

The effect of high salt concentration and pH on the binding of globular protein to polycation at different molar masses has been investigated by dynamic light scattering (DLS), turbidimetry and electrostatic modeling for the protein. In dilute concentration regime, DLS and pH titrations showed three remarkable pH transitions: pHc, the pH where soluble complexes of bovine serum albumin (BSA) and linear synthetic Polyethylenemine (PEI) are formed, pHc’ presents the end of primary soluble complex and pHφ presents the first appearance of microcoacervate droplets. All pH transitions increase with increasing NaCl concentration. The Adaptive Poisson-Boltzmann Solver (APBS) identify with precision the functional sites at the surface of BSA and shows that the strength of electrostatic interactions depends hugely on the variation of pH and ionic strength. At a very high concentration of salt, no remarkable effect on a mixture formed of a long chain of polycation and globular protein.

Intra- and Interpolyelectrolyte Complexes of Polyampholytes

At present, a large amount of research from experimental and theoretical points of view has been done on interpolyelectrolyte complexes formed by electrostatic attractive forces and/or interpolymer complexes stabilized by hydrogen bonds. By contrast, relatively less attention has been given to polymer⁻polymer complex formation with synthetic polyampholytes (PA). In this review the complexation of polyampholytes with polyelectrolytes (PE) is considered from theoretical and application points of view. Formation of intra- and interpolyelectrolyte complexes of random, regular, block, dendritic polyampholytes are outlined. A separate subsection is devoted to amphoteric behavior of interpolyelectrolyte complexes. The realization of the so-called "isoelectric effect" for interpolyelectrolyte complexes of water-soluble polyampholytes, amphoteric hydrogels and cryogels with respect to surfactants, dye molecules, polyelectrolytes and proteins is demonstrated.

Aspects of the Belousov-Zhabotinsky Reaction inside a Self-Oscillating Polymer Brush

We have developed a novel polymer brush surface exhibiting autonomous swelling-deswelling changes driven by the Belousov-Zhabotinsky (BZ) reaction, that is, the self-oscillating polymer brush. In this system, the ruthenium tris(2,2'-bipyridine) [Ru(bpy)₃] catalyst-conjugated polymer chains are densely packed on the solid substrate. It is expected that the BZ reaction in the polymer brush would be influenced by the immobilization effect of the catalyst. To clarify the effect of the immobilization of the catalyst on the self-oscillating polymer brush, the self-oscillating behavior of the polymer brush was investigated by comparing it with that of other self-oscillating polymer materials, the free polymer, and the gel particle under various initial substrate concentrations. The initial substrate dependency of the oscillating period for the polymer brush was found to be different from those for the free polymer and the gel particle. Furthermore, the oscillatory waveform was analyzed on the basis of the Field-Körös-Noyes model. These investigations revealed that the dense immobilization of the self-oscillating polymer on the surface restricted accessibility for the Ru(bpy)₃ moiety. These findings would be helpful in understanding the reaction-diffusion mechanism in the polymer brush, which is a novel reaction medium for the BZ reaction.

Immobilization of Ulp1 protease on NHS-activated Sepharose: a useful tool for cleavage of the SUMO tag of recombinant proteins

OBJECTIVE

To fabricate an active and stable enzyme through covalent immobilization, a Ubl-specific protease (Ulp1) was used to cleave small ubiquitin-like modifier (SUMO) fusion proteins.

RESULTS

We immobilized Ulp1 on N-hydroxysuccinimide (NHS)-activated Sepharose with a coupling efficiency of 1.7 mg/ml. The immobilized Ulp1 maintains 95% substrate-cleavage ability and significantly enhances pH and thermal stability, especially can withstand pH of 10.5. Besides resistance against some small molecules, the immobilized Ulp1 can tolerate 15% (v/v) DMSO and 20% (v/v) ethanol. It can be reused for more than 15 batch reactions with 90% activity retention. This provides a fast purification system to quickly obtain cleaved recombinant proteins with 95% purity from cell lysates with the application of immobilized Ulp1.

CONCLUSIONS

Ulp1 used in immobilization form is a potentially useful tool for cleavage of SUMO-tagged proteins and may reduce time and cost of protein purification.

Self assembling nanocomposites for protein delivery: supramolecular interactions of soluble polymers with protein drugs

Translation of therapeutic proteins to pharmaceutical products is often encumbered by their inadequate physicochemical and biopharmaceutical properties, namely low stability and poor bioavailability. Over the last decades, several academic and industrial research programs have been focused on development of biocompatible polymers to produce appropriate formulations that provide for enhanced therapeutic performance. According to their physicochemical properties, polymers have been exploited to obtain a variety of formulations including biodegradable microparticles, 3-dimensional hydrogels, bioconjugates and soluble nanocomposites. Several soluble polymers bearing charges or hydrophobic moieties along the macromolecular backbone have been found to physically associate with proteins to form soluble nanocomplexes. Physical complexation is deemed a valuable alternative tool to the chemical bioconjugation. Soluble protein/polymer nanocomplexes formed by physical specific or unspecific interactions have been found in fact to possess peculiar physicochemical, and biopharmaceutical properties. Accordingly, soluble polymeric systems have been developed to increase the protein stability, enhance the bioavailability, promote the absorption across the biological barriers, and prolong the protein residence in the bloodstream. Furthermore, a few polymers have been found to favour the protein internalisation into cells or boost their immunogenic potential by acting as immunoadjuvant in vaccination protocols.

Glycosaminoglycans as polyelectrolytes

One of the barriers to understanding structure-property relations for glycosaminoglycans has been the lack of constructive interplay between the principles and methodologies of the life sciences (molecular biology, biochemistry and cell biology) and the physical sciences, particularly in the field of polyelectrolytes. To address this, we first review the similarities and differences between the physicochemical properties of GAGs and other statistical chain polyelectrolytes of both natural and abioitic origin. Since the biofunctionality and regulation of the structures of GAGs is intimately connected with interactions with their cognate proteins, we particularly compare and contrast aspects of protein binding, i.e. effects of both GAGs and other polyelectrolytes on protein stability, protein aggregation and phase behavior. The protein binding affinities and their dependences on pH and ionic strength for the two groups are discussed not only in terms of observable differences, but also with regard to contrasting descriptions of the bound state and the role of electrostatics. We conclude that early studies of the heparin-Antithromin system, proceeding to a large extent through the methods and models of protein chemistry and drug discovery, established not only many enabling precedents but also constraining paradigms. Current studies on heparan sulfate and chondroitin sulfate seem to reflect a more ecumenical view likely to be more compatible with concepts from physical and polymer chemistry.

pH effects on the hyaluronan hydrolysis catalysed by hyaluronidase in the presence of proteins: Part I. Dual aspect of the pH-dependence

Hyaluronan (HA) hydrolysis catalysed by hyaluronidase (HAase) is strongly inhibited when performed at a low ratio of HAase to HA concentrations and at low ionic strength. This is because long HA chains can form non-active complexes with HAase. Bovine serum albumin (BSA) is able to compete with HAase to form electrostatic complexes with HA so freeing HAase which then recovers its catalytic activity. This BSA-dependence is characterised by two main domains separated by the optimal BSA concentration: below this concentration the HAase activity increases when the BSA concentration is increased, above this concentration the HAase activity decreases. This occurs provided that HA is negatively charged and BSA is positively charged, i.e. in a pH range from 3 to 5.25. The higher the pH value the higher the optimal BSA concentration. Other proteins can also modulate HAase activity. Lysozyme, which has a pI higher than that of BSA, is also able to compete with HAase to form electrostatic complexes with HA and liberate HAase. This occurs over a wider pH range that extends from 3 to 9. These results mean that HAase can form complexes with HA and recover its enzymatic activity at pH as high as 9, consistent with HAase having either a high pI value or positively charged patches on its surface at high pH. Finally, the pH-dependence of HAase activity, which results from the influence of pH on both the intrinsic HAase activity and the formation of complexes between HAase and HA, shows a maximum at pH 4 and a significant activity up to pH 9.

Structural studies of agar–gelatin complex coacervates by small angle neutron scattering, rheology and differential scanning calorimetry

Agar-gelatin complex coacervates are studied by small angle neutron scattering (SANS), rheology (in both flow and temperature scan modes) and differential scanning calorimetry (DSC) in order to probe the microscopic structure of this dense protein-polysaccharide-rich phase. DSC and isochronal temperature sweep (rheology) experiments yielded a characteristic temperature at approximately 35+/-2 degrees C. Rheology data revealed a second characteristic temperature at approximately 75+/-5 degrees C which was absent in DSC thermograms. In the flow mode, shear viscosity (eta) was found to scale with (Carreau model) applied shear rate (gamma ) as: eta(gamma ) approximately (gamma )(-k) with k=1.2+/-0.2 indicating non-Newtonian and shear-thinning features independent of ionic strength. The static structure factor S(q) deduced from SANS data in the low wave vector (0.018 A(-1)<q<0.072 A(-1)) region was fitted to Debye-Bueche function, S(q) approximately 1/(1+zeta(2)q(2))(2) that yielded a size zeta approximately 220+/-20 A identified with the size of the inhomogeneities present. In the high-q region, called the Ornstein-Zernike regime, S(q) approximately 1/(1+xi(2)q(2)) gave correlation length xi approximately 12+/-2A. The results taken together imply the existence of a weakly interconnected and heterogeneous network structure inside the coacervate phase. Structural features of this material are compared with those of agar and gelatin gel, and gelatin coacervate.

Intermolecular complexation and phase separation in aqueous solutions of oppositely charged biopolymers

Turbidity measurements performed at 450nm were used to follow the process of complex formation, and phase separation in gelatin-agar aqueous solutions. Acid (Type-A) and alkali (Type-B) processed gelatin (polyampholyte) and agar (anionic polyelectrolyte) solutions, both having concentration of 0.1% (w/v) were mixed in various proportions, and the mixture was titrated (with 0.01 M HCl or NaOH) to initiate associative complexation that led to coacervation. The titration profiles clearly established observable transitions in terms of the solution pH corresponding to the first occurrence of turbidity (pH(C), formation of soluble complexes), and a point of turbidity maximum (pH(phi), formation of insoluble complexes). Decreasing the pH beyond pH(phi) drove the system towards precipitation. The values of pH(C) and pH(phi) characterized the initiation of the formation of intermolecular charge neutralized soluble aggregates, and the subsequent formation of microscopic coacervate droplets. These aggregates were characterized by dynamic light scattering. It was found that Type-A and -B gelatin samples formed soluble intermolecular complexes (and coacervates) with agar molecules through electrostatic and patch-binding interactions, respectively.

A mycelium with polyelectrolyte complex-bunched hyphae: preparation and fermentation performance

We studied the immobilization of a mycelium (Aspergillus niger) using the working hypothesis as follows: (a) when polycation was added to the cell suspension, a few parts of it would bind on the surface of a hypha, allowing to gather the hyphae in part but not all; (b) upon further addition of polyanion, such a gathering of the hyphae is tightly bunched by the polyelectrolyte complex (PEC) which is resulted from the remaining polycation; (c) as a result, a mycelium with partially bunched hyphae can be obtained. Potassium poly(vinyl alcohol) sulfate and trimethylammonium glycol chitosan iodide [6-O-(2-hydroxyethyl-2-(trimethylamonio)-chitosan iodide) were used as the polyanion and the polycation, respectively. The optical and electron microscopic analyses showed that our immobilized cell contains many of PEC-bunched hyphae. The sedimentation rate increased with the weight ratio of PEC to dry cells and leveled off at the weight ratio larger than 0.5. The gluconic acid production from glucose was studied by a semi-large scale (1l) cultivation of the imobilized and free cells using a jar fermentor. It was found that an apparent specific activity of the immobilized cells for glucose oxidation becomes 1.44 times that of the free cells even at a high cell density of 40 g/l.

Polyelectrolyte gel transitions: experimental aspects of charge inhomogeneity in the swelling and segmental attractions in the shrinking

This paper aims to provide a systematic discussion based on our experimental results both previously published and unpublished, to promote better understanding of volume-phase transitions in polyelectrolyte gels. Special attention was paid to the distribution of network charges as well as to the attractive interaction among polymer segments. From looking at how these effects appear in the swelling curves, an exploration of the nature of polyelectrolyte gel transitions was attempted. Two sorts of polyelectrolyte gels, temperature-responsive ionic gels based on N-isopropylacrylamide (NIPA) and cationic poly(ethyleneimine) (PEI) gels, were mainly employed with various modifications. The charge inhomogeneity within the gel phase was created by surfactant binding, immobilized enzyme reaction and physical entrapment of polyions. The attractive interactions holding the gel in a collapsed state were studied in comparison with phase separations of the corresponding linear polyelectrolyte. The main conclusions are summarized as follows: (i) The charge inhomogeneity exhibits a large influence on the volume transition in ionic gels. (ii) Hydrogen bonding and hydrophobic association, other than electrostatic attraction, can be considered to play an important role in the segmental association. (iii) Stably associated segments via one or more of these attractive interactions causes a large hysteresis in the swelling process, in which the repulsive interaction among the fixed charges on the network is dominant as shown in the Katchalsky's model. (iv) A distribution of "neutral but hydrophilic" moieties (e.g., ion pair or salt-linkage formed between the opposite charged groups) within the gel shows a marked effect on the temperature-induced volume collapse, the aspect of which is similar to that observed in the gels with a charge inhomogeneity.

The effects of poly(ethylene glycol) on the solution structure of human serum albumin

Protein physical and chemical properties can be altered by polymer interaction. The presence of several high affinity binding sites on human serum albumin (HSA) makes it a possible target for many organic and polymer molecules. This study was designed to examine the interaction of HSA with poly(ethylene glycol) (PEG) in aqueous solution at physiological conditions. Fourier transform infrared, ultraviolet-visible, and CD spectroscopic methods were used to determine the polymer binding mode, the binding constant, and the effects of polymer complexation on protein secondary structure. The spectroscopic results showed that PEG is located along the polypeptide chains through H-bonding interactions with an overall affinity constant of K = 4.12 x 10(5) M(-1). The protein secondary structure showed no alterations at low PEG concentration (0.1 mM), whereas at high polymer content (1 mM), a reduction of alpha-helix from 59 (free HSA) to 53% and an increase of beta-turn from 11 (free HSA) to 22% occurred in the PEG-HSA complexes (infrared data). The CDSSTR program (CD data) also showed no major alterations of the protein secondary structure at low PEG concentrations (0.1 and 0.5 mM), while at high polymer content (1 mM), a major reduction of alpha-helix from 69 (free HSA) to 58% and an increase of beta-turn from 7 (free HSA) to 18% was observed.

Anomalous self-assembly of gelatin in ethanol-water marginal solvent

Light scattering, rheology, and atomic force microscope (AFM) studies have been performed on solutions of a polyampholyte (gelatin) prepared in water-ethanol marginal solvent. At ethanol concentration approximately 45+/-2% v/v anomalous aggregation led to formation of fractal (on hydrophilic substrates; glass, quartz and silicon) aggregate of polypeptide molecules having fractal dimension d(f) in 2D=1.60+/-0.08. The time evolution morphology of these self-assembled and self-organized structures formed on hydrophilic substrates was driven by selective ethanol evaporation and was observed by an AFM. These fractal aggregates eventually transformed into near-spherical clusters with fractal corona having same fractal dimension (d(f)=1.58+/-0.05) and finally, the corona separated and regular aggregates were formed. The kinetics of aggregation on substrates could be modeled through random sequential adsorption of particles with continuum power-law size distribution. The temporal growth of aggregate hydrodynamic radius R(h)(t) and scattered intensity I(s)(t) measured in the bulk were observed to exhibit; R(h)-t(z) and I(s)-t(z)-with z=1/d(f), giving a fractal dimension d(f) in 3D approximately equal to 2.6+/-0.2, which is discussed within the framework of Smoluchowski aggregation kinetics. This growth in R(h) is accompanied by narrowing down of the particle size distribution. Solution rheology at this ethanol concentration revealed minimum thixotropy and maximum infinite shear viscosity features.

Thermodynamic parameters of beta-lactoglobulin-pectin complexes assessed by isothermal titration calorimetry

Isothermal titration calorimetry (ITC) was used to determine the binding constant, stoichiometry, enthalpy, and entropy of beta-lactoglobulin/low- and high-methoxyl pectin (beta-lg-LM- and HM-pectin) complexes at 22 degrees C and at pH 4. The binding isotherms revealed the formation of soluble intrapolymer complexes (C1) further followed by their aggregation in interpolymer complexes (C2). The interaction between beta-lg and LM- or HM-pectin in C1 and C2 occurred spontaneously with a Gibbs free energy around -10 kcal/mol. The C1 were enthalpically driven, whereas enthalpic and entropic factors were involved in the C2 formation. Because ITC did not allow the dissociation of different enthalpic contributions, the values measured as pectin and beta-lg interacted could partially be attributed to conformational changes. The C1 had a binding stoichiometry of 8.3 and 6.1 beta-lg molecules complexed per LM- or HM-pectin molecule, respectively. The C2 had about 16.5 and 15.1 beta-lg molecules complexed per LM- and HM-pectin, respectively.

Systematic of alcohol-induced simple coacervation in aqueous gelatin solutions

Turbidity measurements performed at 450 nm were used to follow the process of simple coacervation when 1% (w/v) aqueous alkali processed gelatin (type-B) solutions were titrated with methanol, ethanol, propanol, and tert-butyl alcohol at various pHs of the solution ranging from pH = 5 to 8 and ionic strengths varying from I = 0.01 to 0.1 M NaCl. The titration profiles clearly established the transition points in terms of the percentage of volume of alcohol added relative to that of solvent corresponding to the first occurrence of turbidity (Vt) and a point of turbidity maximum (Vp). Addition of more alcohol drove the system toward precipitation. The values of Vt and Vp characterized the initiation of intramolecular folding and intermolecular aggregate formation of the charge neutralized gelatin molecules and the subsequent micro coacervate droplet formation. The state of intermolecular aggregates and that of folded gelatin molecules could be characterized by dynamic laser light scattering experiments, which implied spontaneous segregation of particle sizes preceding coacervation. The aggregates constitute the coacervate phase while the folded gelatin molecules mostly stay dispersed in the supernatant. The data taken together reveal the role played by solution entropy in addition to that of electrostatic and solute-solvent interactions, which had been overlooked hitherto.

Intramolecular complex formation of poly(N-isopropylacrylamide) with human serum albumin

Complexation of human serum albumin (HSA) with poly(N-isopropylacrylamide) (PNIPA) ranging in molecular weight (M(PNIPA)) from 2.1 x 10(4) to 1.72 x 10(6) was studied in an aqueous system (pH 3) containing NaCl as a supporting salt. Dynamic light scattering, static light scattering, electrophoretic light scattering, and dialyzing techniques were used as the experimental tool in a suitable combination. The measurements were performed mainly at 25 degrees C and at 0.01 M NaCl as a function of mixing ratio (r(m), molar ratio of PNIPA to HSA). The results of DLS and ELS evidently demonstrated the formation of a water-soluble complex through mixing of HSA and PNIPA. A detailed analysis of SLS data with the aid of dialysis data revealed that the resulting complex is an "intramolecular" complex consisting of a PNIPA chain with several of bound HSA molecules. Both hydrodynamic radius (R(h)) and radius gyration (R(g)) of intramolecular complexes decreased as r(m) was increased. This result correlated well to the fact that the number (n) of bound proteins per polymer decreases with increasing r(m). The size and the molar mass of the complex became large depending on M(PNIPA), but the increase of M(PNIPA) led to a decrease in n at r(m) < 1. The increase in NaCl concentration from 0.01 to 0.3 M brought about the increase in the size and the molar mass of an intramolecular HSA-PNIPA complex prepared at r(m) = 1.1. This was found to be due to an increase of n. A similar trend was observed when temperature rose from 25 to 32 degrees C (close to lower critical solution temperature of PNIPA). However, the effect of temperature on the increase of was strong in comparison with that of ionic strength. On the basis of these results obtained, the complexation mechanism was discussed in detail.

Identification by integrated computer modeling and light scattering studies of an electrostatic serum albumin-hyaluronic acid binding site

Dynamic light scattering and turbidimetry, carried out on solutions of hyaluronic acid (HA) and bovine or human serum albumin (SA) at fixed ionic strength (I), revealed a critical pH corresponding to the onset of HA-SA soluble complex formation. Subsequent reduction of pH below pH(c), corresponding to an increase in protein net positive charge, results in phase separation of the complex. The sensitivity of pH(c) to I indicated the primacy of electrostatic interactions in this process. Since pH(c) was always above the pK(a) of HA, these effects could be attributed to the influence of protein charge. The electrostatic potential around HSA was modeled using DelPhi (MSI) under pH, I conditions corresponding to incipient binding, phase separation, and noninteraction. At all incipient binding conditions (i.e., pH(c), at varying I), an identical region of positive potential 5 A from the protein van der Waals surface appeared. This unique domain intensified with a decrease in pH or I (corresponding to stronger binding), and diminished with an increase in pH or I (i.e., at noninteracting conditions). The size and low curvature of this domain could readily accommodate a 12 nm (decamer) sequence of HA. Simple electrostatic considerations indicate an electrostatic binding energy for the formation of this complex of ca. 1 kT, consistent with the condition of incipient complex formation. We suggest that such weak electrostatic binding may characterize nonspecific interactions for other protein-gylcosaminoglycan pairs.

Coimmobilization of gluconolactonase with glucose oxidase for improvement in kinetic property of enzymatically induced volume collapse in ionic gels

The object of this paper is to provide an enzymatic means to attain faster swelling or shrinking kinetics of polyelectrolyte gels that undergo volume phase transition as an immobilized enzyme reaction sets in. For this, we studied the coimmobilization of gluconolactonase (GL) with glucose oxidase (GOD). A gel used was in the shape of a small cylinder (several hundred micrometers in diameter) and composed of a lightly cross-linked copolymer of N-isopropylacrylamide and acrylic acid. GL was isolated from Aspergillus niger and purified about 100-fold. It was found that in a substrate solution containing glucose, the gel with the coimmobilized GL and GOD shrinks very rapidly. The shrinking rate was identical to that of the enzyme-free gel that undergoes a shrinking transition in response to a sudden pH change of the outer medium from 7 to 5. This indicates the rate-limiting step in the shrinking process to be diffusion of the networks, but not the enzyme reaction. In the gel with singly immobilized GOD, a very slow shrinking was observed because the process is governed by the enzyme reaction. These results were discussed in full in connection with an enzymatically induced decrease in pH within and in the vicinity of the gel phase. As a result, it has become apparent that the faster shrinking kinetics in the coimmobilized enzyme system is attained by the GL-catalyzed hydrolysis of D-glucono-delta-lactone resulting from the oxidation of glucose with GOD.

Light scattering, CD, and ligand binding studies of ferrihemoglobin-polyelectrolyte complexes

Quasi-elastic light scattering (QELS), electrophoretic light scattering (ELS), CD spectroscopy, and azide binding titrations were used to study the complexation at pH 6.8 between ferrihemoglobin and three polyelectrolytes that varied in charge density and sign. Both QELS and ELS show that the structure of the soluble complex formed between ferrihemoglobin and poly(diallyldimethylammonium chloride) [PDADMAC] varies with protein concentration. At fixed 1.0 mg/mL polyelectrolyte concentration, protein addition increases complex size and decreases complex mobility in a tightly correlated manner. At 1.0 mg/mL of greater protein concentration, a stable complex is formed between one polyelectrolyte chain and many protein molecules (i.e., an intrapolymer complex) with apparent diameter approximately 2.5 times that of the protein-free polyelectrolyte. Under conditions of excess polyelectrolyte, each of the three ferrihemoglobin-polyelectrolyte solutions exhibits a single diffusion mode in QELS, which indicates that all protein molecules are complexed. CD spectra suggest little or no structural disruption of ferrihemoglobin upon complexation. Azide binding to the ferrihemoglobin-poly(2-acrylamide-2-methylpropanesulfonate) [PAMPS] complex is substantially altered relative to the polyelectrolyte-free protein, but minimal change in induced by complexation with an AMPS-based copolymer of reduced linear charge density. The change in azide binding induced by PDADMAC is intermediate between that of PAMPS and its copolymer.