Hollow microgel based ultrathin thermoresponsive membranes for separation, synthesis, and catalytic applications

Thermoresponsive core-shell microgels with degradable core are synthesized via surfactant based free radical polymerization using N,N'-(1,2-dihydroxy-ethylene)bis(acrylamide) (DHEA) as a cross-linker for core preparation. The 1,2-glycol bond present in DHEA is susceptible to NaIO4 solution, and thus, the structure can be cleaved off resulting in hollow microgel. Ultrathin membranes are prepared by suction filtration of a dilute suspension of core-shell microgels over a sacrificial layer of Cd(OH)2 nanostrand coated on track etched membrane. After removal of the degraded cores from microgels, the membranes are cross-linked with glutaraldehyde and the nanostrands are removed by passing a 10 mM HCl solution. The prepared membranes are thoroughly characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and dynamic contact angle for morphology, thermoresponsive, and hydrophilic properties, respectively. The prepared membranes showed thermoresponsive permeation behavior and remarkable separation performance for low molecular weight dyes and lysozyme protein. These membranes are also used to synthesize gold nanoparticles and immobilize lactate dehydrogenase enzyme for catalytic and biocatalytic application. The results for water permeation, solute rejection, and ability to immobilize gold nanoparticles and enzymes showed its wide range of applicability. Furthermore, the synthesis of hollow microgel is simple and environmentally friendly, and the membrane preparation is easy, scalable, and other microgel systems can also be used. These responsive membranes constitute a significant contribution to advanced separation technology.

Sodium hexadecyl sulfate as an interfacial substance adjusting the adsorption of a protein on carbon nanotubes

Carbon nanotubes (CNTs) were functionalized with sodium hexadecyl sulfate (SHS). The lysozyme adsorbed on the SHS-CNTs exhibited a higher activity than that immobilized on the nonfunctionalized CNTs. To explain the experimental results and explore the mechanism of lysozyme adsorption, large-scale molecular dynamics simulations have been performed for a four-component system, including lysozyme, SHS, CNTs in explicit water. It has been found that the assembled SHS molecules form a soft layer on the surface of CNTs. The interactions between lysozyme and SHS induce the rearrangement of SHS molecules, forming a saddle-like structure on the CNT surface. The saddle-like structure fits the shape of the lysozyme, and the active-site cleft of the lysozyme is exposed to the water phase. Whereas, for the lysozyme adsorbed on the nonfunctionalized CNT, due to the hydrophobic interactions, the active-site cleft of the enzyme tends to face the wall of the CNT. The results of this work demonstrate that the SHS molecules as the interfacial substance have a function of adjusting the lysozyme with an appropriate orientation, which is favorable for the lysozyme having a higher activity.

Lysozyme and defense peptides as suppressors of phenoloxidase activity in Galleria mellonella

The prophenoloxidase (proPO) cascade supplies quinones and other reactive compounds for melanin formation, protein cross-linking, hemolymph coagulation, and killing of microbial invaders as well as parasites. The high cytotoxicity of the generated compounds requires a strict control of the activation of the proPO system and phenoloxidase (PO) activity to minimize damage to host tissues and cells. The PO activity in hemolymph of Escherichia coli challenged Galleria mellonella larvae increased, with a temporal drop 1 h after the challenge, reaching the highest level 24 h after the challenge. In the present study, a potential role of G. mellonella defense peptides and lysozyme in controlling the proPO system was investigated. The effects of purified defense peptides (anionic peptides 1 and 2, cecropin D-like peptide, Galleria defensin, proline-rich peptides 1 and 2) and lysozyme were analyzed. Four compounds, namely lysozyme, Galleria defensin, proline-rich peptide 1, and anionic peptide 2, decreased the hemolymph PO activity considerably, whereas the others did not affect the enzyme activity level. Our results indicate that these hemolymph factors could play multiple and distinct roles in the insect immune response.

The Amino Acid Sequence of Satyr Tragopan Lysozyme and Its Activity

The amino acid sequence of satyr tragopan lysozyme and its activity was analyzed. Carboxymethylated lysozyme was digested with trypsin and the resulting peptides were sequenced. The established amino acid sequence had three amino acid substitutions at positions 103 (Asn to Ser), 106 (Ser to Asn), and 121 (His to Gln) comparing with Temminck's tragopan lysozyme and five amino acid substitutions at positions 3 (Phe to Tyr), 15 (His to Leu), 41 (Gln to His), 101 (Asp to Gly) and 103 (Asn to Ser) with chicken lysozyme. The time course analysis using N-acetylglucosamine pentamer as a substrate showed a decrease of binding free energy change, 1.1 kcal/mol at subsite A and 0.2 kcal/mol at subsite B, between satyr tragopan and chicken lysozymes. This was assumed to be responsible for the amino acid substitutions at subsite A-B at position 101 (Asp to Gly), however another substitution at position 103 (Asn to Ser) considered not to affect the change of the substrate binding affinity by the observation of identical time course of satyr tragopan lysozyme with turkey and Temminck's tragopan lysozymes that carried the identical amino acids with chicken lysozyme at this position. These results indicate that the observed decrease of binding free energy change at subsites A-B of satyr tragopan lysozyme was responsible for the amino acid substitution at position 101 (Asp to Gly).

[Highly active fractions of the medicinal leech recombinant destabilase-lysozyme]

From the highly purified but lowly active recombinant protein Destabilas-Lysozyme (Dest-Lys) by use cation-exchange column TSK CM 3-SW chromatography, it was separated non-active fraction IV, contained 90% of protein. Fractions I, II and III, represented proteins with lysozyme and isopeptidase activities. Their lysozyme activity correlates with the activity of natural Des-Lys. The ratio of the activities in fractions I - III is such, that maximal lysozyme activity is concentrated in fraction III, isopeptidase - in fraction I. It is discussed the possibility of Dest-Lys different functions regulation is depended on the formation of protein complex forms.

Purification of PEGylated proteins, with the example of PEGylated lysozyme and PEGylated scFv

PEGylation is a common and highly accepted possibility for half-life prolongation of proteins by increasing the hydrodynamic size. The chromatographic purification of PEGylated protein, using PEG (poly-ethylene glycol) of different PEG chain lengths, with the example of lysozyme and a scFv, is described in detail here, and helpful suggestions for the purification of other PEGylated proteins are listed. The relevant characterization methods for PEGylated proteins, important for the successful purification, are also described. The purification starts with a CEX (cation exchange) chromatography leading to about 95 % purity for polishing HIC (hydrophobic interaction chromatography) is described.

Enzyme characterisation and gene expression profiling of Atlantic salmon chicken- and goose-type lysozymes

Lysozymes represent important innate immune components against bacteria. In this study, Atlantic salmon (Salmo salar) goose (g-) and chicken (c-) types of lysozyme were subjected to protein characterisations and tissue expression analyses. Specific bacterial protein inhibitors of g- and c-type lysozymes were employed to discriminate between respective enzyme activities. Blood, gills and liver contained activities exclusive for the g-type lysozyme. Only haematopoietic organs (head kidney and spleen) contained enzyme activities of both g- and c-lysozyme enzymes and c-type activity was not found outside these organs. Gene transcript levels proportional to enzyme activity levels were detected for the g-type lysozyme but not for the c-type. In vitro studies revealed significant induction of c-type gene expression and enzyme activity in macrophages after incubation with lipopolysaccharide (LPS) while expression of the g-type lysozyme gene was unaffected. The activity of purified native c-type enzyme was profoundly reduced by divalent cations and displayed low tolerance to monovalent cations, while the native g-type lysozyme was stimulated by monovalent cations and tolerated low concentrations of divalent cations. Activities of both enzymes increased with temperature elevations up to 60°C. The native g-type lysozyme responses to temperature in particular are in apparent conflict to the ones for the recombinant salmon g-lysozyme. Our results imply separate expression regulations and different functions of c- and g-type lysozymes in salmon. LPS-induced expression of c-type lysozyme and broad constitutive tissue distribution of g-type lysozyme in salmon is different from findings in other studied fish species.

Label-free and reagent-less protein biosensing using aptamer-modified extended-gate field-effect transistors

We have developed biosensors based on an aptamer-modified field-effect transistor (FET) for the detection of lysozyme and thrombin. An oligonucleotide aptamer as a sensitive and specific ligand for these model proteins was covalently immobilized on a gold electrode extended to the gate of FET together with thiol molecules to make a densely packed self-assembled monolayer (SAM). The aptamer-based potentiometry was achieved in a multi-parallel way using a microelectrodes array format of the gate electrode. A change in the gate potential was monitored in real-time after introduction of a target protein at various concentrations to the functionalized electrodes in a buffer solution. Specific protein binding altered the charge density at the gate/solution interface, i.e., interface potential, because of the intrinsic local net-charges of the captured protein. The potentiometry successfully determined the lysozyme and thrombin on the solid phase with their dynamic ranges 15.2-1040 nM and 13.4-1300 nM and the limit of detection of 12.0 nM and 6.7 nM, respectively. Importantly, robust signals were obtained by the specific protein recognition even in the spiked 10% fetal bovine serum (FBS) conditions. The technique herein described is all within a complementary metal oxide semiconductor (CMOS) compatible format, and is thus promising for highly efficient and low cost manufacturing with the readiness of downsizing and integration by virtue of advanced semiconductor processing technologies.

Chemometric method of spectra analysis leading to isolation of lysozyme and CtDNA spectra affected by osmolytes

In this paper we present a chemometric method of analysis leading to isolation of Fourier transform infrared (FT-IR) spectra of biomacromolecules (HEW lysozyme, ctDNA) affected by osmolytes (trimethylamine-N-oxide and N,N,N-trimethylglycine, respectively) in aqueous solutions. The method is based on the difference spectra method primarily used to characterize the structure of solvent affected by solute. The cyclical usage of factor analysis allows precise information to be obtained on the shape of "affected spectra" of analyzed biomacromolecules. "Affected spectra" of selected biomacromolecules give valuable information on their structure in the presence of the osmolytes in solution, as well as on the level of perturbation in dependence of osmolyte concentration. The method also gives a possibility of insight into the mechanism of interaction in presented types of systems. It can be easily adapted to various chemical and biochemical problems where vibrational or ultraviolet-visible (UV-Vis) spectroscopy is used.

[Bacteriolytic enzymes of blood plasma from sheep]

In the present work the studies ofbacteriolytic factors from sheep blood plasma have been performed. Three novel enzymes have been identified and characterized. Two of them have a molecular weight 15 +/- 2 kDa and able to lyse the gram-negative Escherichia coli bacteria. The third enzyme has a molecular weight 34 +/- 4 kDa and is able to lyse both gram-negative Escherichia coli and gram-positive Micrococcus luteus bacteria. The bacteriolytic reactions have been studied for all three enzymes; particularly, pH-optima have been identified with respect to the substrate. To identify the enzymes trypsinolysis and consequent MALDI-TOF mass spectrometry studies were performed. The results were compared to data from publicly available databases, such as Swiss-Prot, NCBI, MSDB.

Proteolysis in microfluidic droplets: an approach to interface protein separation and peptide mass spectrometry

A versatile microreactor protocol based on microfluidic droplets has been developed for on-line protein digestion. Proteins separated by liquid chromatography are fractionated in water-in-oil droplets and digested in sequence. The microfluidic reactor acts also as an electrospray ionization emitter for mass spectrometry analysis of the peptides produced in the individual droplets. Each droplet is an enzymatic micro-reaction unit with efficient proteolysis due to rapid mixing, enhanced mass transfer and automated handling. This droplet approach eliminates sample loss, cross-contamination, non-specific absorption and memory effect. A protein mixture was successfully identified using the droplet-based micro-reactor as interface between reverse phase liquid chromatography and mass spectrometry.

Potential possibilities of production, modification and practical application of lysozyme

INTRODUCTION

Lysozyme, taking a stand in many biological fluids and tissues of a large number of living organisms, is a strongly basic protein. Hen egg white is its rich source and from this source enzyme can be obtained on a commercial scale as a preparation of biological activity. Monomer of lysozyme is known as hydrolase cutting the b-1-4 glycosidic bond, but its dimeric form received after modification of monomer form, exerts different and new valuable properties. In this study we indicated ways of production and modification of lysozyme and possibilities of its practical application.

MATERIAL AND METHODS

The material for producing of lysozyme was fresh egg white. Enzyme was isolated by direct crystallization, ion-exchange chromatographic and utrafiltration methods. Lysozyme received by ion-exchange method has been used for modification. Modification of enzyme was carried out by chemical, chemical-thermal, thermal and membrane methods.

RESULTS

The presented methods of lysozyme isolation from hen egg white yielded good results. Depending on employed procedure it was recovered from 20 to 85 % of enzyme. However, after modification approximately the quantity of 50-70% of polymerized enzyme was received, which contained from 30-40% of dimer.

CONCLUSION

The method of isolating and modifying lysozyme can be successfully used to produce high active preparation of enzyme. Lysozyme monomer, and especially its modified form, shows the possibility of wide use not only in food industry, but also in medicine, pharmacology and veterinary medicine.

[Lysozyme activity of the salivary gland secretion of the medicinal leech H. verbana, H. medicinalis and H. orientalis]

Salivary gland secretions of three species of the medicinal leech differ in the level of lysozyme peptidoglycan-lysing activity. Using the synthetic fluorogenic substrate, 4-methyl-umbelliferyl tetra N-acetyl-beta-chitotetraosid, the glycosidase activity (as one of peptidoglycan-lysing activities) of salivary gland secretion of three species of the medicinal leech was quantitatively evaluated in comparison with egg lysozyme. It is supposed, that lysozyme activity of the leech secretions is determined not only by 5 isoforms of destabilase-lysozyme, but by some other enzymes which can utilize this substrate. These may be lysozymes other than i- (invertebrate) lysozymes (such as destabilase-lysozyme, or related enzymes).

Construction of affinity changeable antibody in response to Ca2+

Immunoaffinity chromatography is a powerful method for purification of proteins because of the high selectivity and avidity of antibodies. Due to the strength of antigen-antibody binding, however, elution of proteins bound to antibodies that are covalently immobilized on the column is performed by temporary denaturation of the antibody. Therefore, the development of milder elution conditions could improve the recovery of the antibodies and prolong the life of the immunoaffinity column. We describe the design and construction of an antibody that changes its affinity in response to external stimuli. The heavy chain and light chain of a single chain Fv of the D1.3 antibody against hen egg-white lysozyme (HEL) were fused at the N- and C-termini, respectively, of the calmodulin-M13 fusion protein. The affinity of this fusion protein for HEL could be modulated by changing the Ca(2+) concentration.

Lysozyme contamination facilitates crystallization of a heterotrimeric cortactin-Arg-lysozyme complex

Crystallization of contaminating proteins is a frequently encountered problem for macromolecular crystallographers. In this study, an attempt was made to obtain a binary cocrystal structure of the SH3 domain of cortactin and a 17-residue peptide from the Arg nonreceptor tyrosine kinase encompassing a PxxPxxPxxP (PxxP1) motif. However, cocrystals could only be obtained in the presence of trace amounts of a contaminating protein. A structure solution obtained by molecular replacement followed by ARP/wARP automatic model building allowed a 'sequence-by-crystallography' approach to discover that the contaminating protein was lysozyme. This 1.65 Å resolution crystal structure determination of a 1:1:1 heterotrimeric complex of Arg, cortactin and lysozyme thus provides an unusual `caveat emptor' warning of the dangers that underpurified proteins harbor for macromolecular crystallographers.

Quantification of protein deposits on silicone hydrogel materials using stable-isotopic labeling and multiple reaction monitoring

This study was designed to use multiple reaction monitoring (MRM) for accurate quantification of contact lens protein deposits. Worn lenses used with a multipurpose disinfecting solution were collected after wear. Individual contact lenses were extracted and then digested with trypsin. MRM in conjunction with stable-isotope-labeled peptide standards was used for protein quantification. The results show that lysozyme was the major protein detected from both lens types. The amount of protein extracted from contact lenses was affected by the lens material. Except for keratin-1 (0.83 ± 0.61 vs 0.77 ± 0.20, p = 0.81) or proline rich protein-4 (0.11 ± 0.04 vs 0.15 ± 0.12, p = 0.97), the amounts of lysozyme, lactoferrin, or lipocalin-1 extracted from balafilcon A lenses (12.9 ± 9.01, 0.84 ± 0.50 or 2.06 ± 1.6, respectively) were significantly higher than that extracted from senofilcon A lenses (0.88 ± 0.13, 0.50 ± 0.10 or 0.27 ± 0.23, respectively) (p < 0.05). The amount of protein extracted from contact lenses was dependent on both the individual wearer and the contact lens material. This may have implications for the development of clinical responses during lens wear for different people and with different types of contact lenses. The use of MRM-MS is a powerful analytical tool for the quantification of specific proteins from single contact lenses after wear.

Toroidal coil chromatography: the effect of scale-up and "g" field on stage efficiency

Selected test results have been taken from various publications and resolution and stage efficiency measured using an established model. All experiments used the same sample and, where possible, the same sample loading. The results show that stage mixing efficiencies have increased from 1.1% in 1998 to greater than 25% in the latest scaled-up version of a Toroidal coil chromatography (TCC) instrument working at 240 g.

Liquid scintillation spectrometry of tritium in studying lysozyme behavior in aqueous/organic liquid systems. The influence of the organic phase

Liquid scintillation spectrometry of tritium in the application of the scintillation phase method was used for studying the adsorption of lysozyme at the liquid/liquid interface and its distribution in the bulk of the system. The goal of this research was to reveal the influence of the nature of the organic phase on the distribution and adsorption ability of the protein when it is placed in a system containing two immiscible liquids. Based on the radiochemical assay distribution coefficients and adsorption isotherms obtained for aqueous/octane, aqueous/p-xylene and aqueous/octanol systems, it was concluded that the interaction of the protein with the interface plays a dominant role in protein behavior in aqueous/organic liquid systems.

Electrophoretic transport of biomolecules through carbon nanotube membranes

Electrophoretic transport of proteins across electrochemically oxidized multi-walled carbon nanotube (MWCNT) membranes has been investigated. A small charged protein, lysozyme, was successfully pumped across MWCNT membranes by an electric field while rejecting larger bovine serum albumin (BSA). Transport of lysozome was reduced by a factor of about 30 in comparison to bulk mobility and consistent with the prediction for hindered transport. Mobilities between 0.33 and 1.4 × 10(-9) m(2) V(-1) s(-1) were observed and are approximately 10-fold faster than comparable ordered nanoporous membranes and consistent with continuum models. For mixtures of BSA and lysozyme, complete rejection of BSA is seen with electrophoretic separations.

Identification of a bacterial inhibitor against g-type lysozyme

Lysozymes are antibacterial effectors of the innate immune system in animals that hydrolyze peptidoglycan. Bacteria have evolved protective mechanisms that contribute to lysozyme tolerance such as the production of lysozyme inhibitors, but only inhibitors of chicken (c-) and invertebrate (i-) type lysozyme have been identified. We here report the discovery of a novel Escherichia coli inhibitor specific for goose (g-) type lysozymes, which we designate PliG (periplasmic lysozyme inhibitor of g-type lysozyme). Although it does not inhibit c- or i-type lysozymes, PliG shares a structural sequence motif with the previously described PliI and MliC/PliC lysozyme inhibitor families, suggesting a common ancestry and mode of action. Deletion of pliG increased the sensitivity of E. coli to g-type lysozyme. The existence of inhibitors against all major types of animal lysozyme and their contribution to lysozyme tolerance suggest that lysozyme inhibitors may play a role in bacterial interactions with animal hosts.

Characterization and expression analysis of a goose-type lysozyme from the rock bream Oplegnathus fasciatus, and antimicrobial activity of its recombinant protein

Lysozyme (muramidase) represents an important defense molecule of the fish innate immune system. Known for its bactericidal properties, lysozyme catalyzes the hydrolysis of β-(1,4)-glycosidic bonds between the N-acetyl glucosamine and N-acetyl muramic acid in the peptidoglycan layer of bacterial cell walls. In this study, the complete coding sequence of a g-type lysozyme (RBgLyz) was identified in the Oplegnathus fasciatus rock bream fish genome by means of multi-tissue normalized cDNA pyrosequencing using Roche 454 GS-FLX™ technology. RBgLyz is composed of 669 bp, with a 567 bp open reading frame that encodes 188 amino acids. Protein motif searches indicated that RBgLyz contains the soluble lytic transglycosylase domain involved in maintaining cell wall integrity. Furthermore, RBgLyz shares significant identity (81.4%) with Chinese perch Siniperca chuatsi. Quantitative real-time RT-PCR analysis results showed that RBgLyz transcripts are constitutively expressed in various tissues from healthy rock breams. In order to determine RBgLyz function in immunity, its expression was analyzed in head kidney following exposure to known immune stimulants or pathogens. RBgLyz transcripts were significantly up-regulated in response to challenge with lipopolysaccharide (LPS) and Edwardsiella tarda, as compared to non-injected control fish. Polyinosinic:polycytidylic acid (poly I:C) dsRNA stimulated a moderate expression of RBgLyz, as did Streptococcus iniae but to a lesser extent. There were no specific time-dependent effects on RBgLyz mRNA expression observed in response to rock bream iridovirus (RBIV) infection. Taken together, the gene expression results indicated that g-type lysozyme plays a role in the innate immune response to LPS, poly I:C, E. tarda and S. iniae in rock bream. Thus, we generated recombinant RBgLyz in an Escherichia coli expression system and characterized its antimicrobial activity. Our results indicated that recombinant RBgLyz had lytic activity against Gram-negative Vibrio salmonicida, Gram-positive Listeria monocytogenes, S. iniae and Micrococcus lysodeikticus. In addition, observations by scanning electron microscope (SEM) confirmed that the cell morphology of M. lysodeikticus was altered in the presence of recombinant RBgLyz.

Site-specific labeling of proteins for single-molecule FRET measurements using genetically encoded ketone functionalities

Studies of protein structure and function using single-molecule fluorescence resonance energy transfer (smFRET) benefit dramatically from the ability to site-specifically label proteins with small fluorescent dyes. Genetically encoding the unnatural amino acid (UAA) p-acetylphenylalanine is an efficient way to introduce commercially available fluorescent tags with high yield and specificity. This protocol describes the expression in Escherichia coli of proteins containing this UAA in response to the amber stop codon TAG. Proteins were purified with high yield and subsequently labeled with the hydroxylamine derivative of Alexa Fluor® 488 functioning as a fluorescent donor dye. The proteins were then labeled via maleimide coupling chemistry at a unique cysteine with the acceptor dye Alexa Fluor® 594 to yield a dual-labeled protein ready for subsequent smFRET observation.

A new lysozyme from the eastern oyster, Crassostrea virginica, and a possible evolutionary pathway for i-type lysozymes in bivalves from host defense to digestion

BACKGROUND

Lysozymes are enzymes that lyse bacterial cell walls, an activity widely used for host defense but also modified in some instances for digestion. The biochemical and evolutionary changes between these different functional forms has been well-studied in the c-type lysozymes of vertebrates, but less so in the i-type lysozymes prevalent in most invertebrate animals. Some bivalve molluscs possess both defensive and digestive lysozymes.

RESULTS

We report a third lysozyme from the oyster Crassostrea virginica, cv-lysozyme 3. The chemical properties of cv-lysozyme 3 (including molecular weight, isoelectric point, basic amino acid residue number, and predicted protease cutting sites) suggest it represents a transitional form between lysozymes used for digestion and immunity. The cv-lysozyme 3 protein inhibited the growth of bacteria (consistent with a defensive function), but semi-quantitative RT-PCR suggested the gene was expressed mainly in digestive glands. Purified cv-lysozyme 3 expressed maximum muramidase activity within a range of pH (7.0 and 8.0) and ionic strength (I = 0.005-0.01) unfavorable for either cv-lysozyme 1 or cv-lysozyme 2 activities. The topology of a phylogenetic analysis of cv-lysozyme 3 cDNA (full length 663 bp, encoding an open reading frame of 187 amino acids) is also consistent with a transitional condition, as cv-lysozyme 3 falls at the base of a monophyletic clade of bivalve lysozymes identified from digestive glands. Rates of nonsynonymous substitution are significantly high at the base of this clade, consistent with an episode of positive selection associated with the functional transition from defense to digestion.

CONCLUSION

The pattern of molecular evolution accompanying the shift from defensive to digestive function in the i-type lysozymes of bivalves parallels those seen for c-type lysozymes in mammals and suggests that the lysozyme paralogs that enhance the range of physiological conditions for lysozyme activity may provide stepping stones between defensive and digestive forms.

Batch purification of high-purity lysozyme from egg white and characterization of the enzyme modified by PEGylation

PEGylation is one of the most promising and extensively studied strategies for improving the pharmacological properties of proteins as well as their physical and thermal stability. Purified lysozyme obtained from hen egg white by batch mode was modified by PEGylation with methoxypolyethyleneglycol succinimidyl succinato (mPEG-SS, MW 5000). The conjugates produced retained full enzyme activity with the substrate glycol chitosan, independent of degree of enzyme modification, although lysozyme activity with the substrate Micrococcus lysodeikticus was altered according to the degree of modification. The conjugate with a low degree of modification by mPEG-SS retained 67% of its enzyme activity with the M. lysodeikticus substrate. The mPEG-SS was also shown to be a highly reactive polymer. The effects of pH and temperature on PEGylated lysozymes indicated that the conjugate was active over a wide pH range and was stable up to 50 degrees C. This conjugate also showed resistance to proteolytic degradation, remained stable in human serum, and displayed greater antimicrobial activity than native lysozyme against Gram-negative bacteria.