Lysozyme Conjugates Research Articles

Nanoscale lines of supported nanogold particles and lysozyme–nanogold conjugates generated by atomic force microscopy in aqueous solution

AbstractThe line‐scan mode is applied in aqueous suspensions of NHS–nanogold and NHS—nanogold–lysozyme conjugates to generate tip‐induced linelike pattern with a width in the nanometer scale. With increasing ionic strength the spontaneous adsorption of the particles to the mica surface can be reduced. The reduction causes an increase in the processing time, which is necessary to form a continuous line composed of the respective particles. The line width increases with increasing loading force. For NHS–nanogold, a minimal line width of about 40 nm could be achieved. The results were used to connect two opposite macroscopic gold contacts about 5 µm apart by a line of NHS–nanogold, which appeared to be of continuous structure down to the nanometer scale, according to the corresponding topography. Copyright © 2006 John Wiley & Sons, Ltd.

In Situ Preparation of Protein−“Smart” Polymer Conjugates with Retention of Bioactivity

Protein-polymer conjugates are widely used in biotechnology and medicine, and new methods to prepare the bioconjugates would be advantageous for these applications. In this report, we demonstrate that bioactive "smart" polymer conjugates can be synthesized by polymerizing from defined initiation sites on proteins, thus preparing the polymer conjugates in situ. In particular, free cysteines, Cys-34 of bovine serum albumin (BSA) and Cys-131 of T4 lysozyme V131C, were modified with initiators for atom transfer radical polymerization (ATRP) either through a reversible disulfide linkage or irreversible bond by reaction with pyridyl disulfide- and maleimide-functionalized initiators, respectively. Initiator conjugation was verified by electrospray-ionization mass spectroscopy (ESI-MS), and the location of the modification was confirmed by muLC-MSMS (tandem mass spectrometry) analysis of the trypsin-digested protein macroinitiators. Polymerization of N-isopropylacrylamide (NIPAAm) from the protein macroinitiators resulted in thermosensitive BSA-polyNIPAAm and lysozyme-polyNIPAAm in greater than 65% yield. The resultant conjugates were characterized by gel electrophoresis and size exclusion chromatography (SEC) and easily purified by preparative SEC. The identity of polymer isolated from the BSA conjugate was confirmed by (1)H NMR, and the polydispersity index was determined by gel permeation chromatography (GPC) to be as low as 1.34. Lytic activities of the lysozyme conjugates were determined by two standard assays and compared to that of the unmodified enzyme prior to polymerization; no statistical differences in bioactivity were observed.

Synthesis of two photolabile poly(ethylene glycol) derivatives for protein conjugation

Two photolabile end functionalised mono methyl poly(ethylene glycol) (PEG) (5000 g/mol) derivatives were prepared. First, a diazopyruvyl derivative (PEG-DAP 4) that undergoes photo induced Wolff rearrangement to give a reactive ketene amide was prepared. Secondly, a commercially available N-hydroxysuccinimide ester of a hexanoyl substituted nitroaryl azide was coupled to PEG to provide the second derivate (PEG-ANPAH 11). Both derivatives were purified by filtration and trituration. They displayed the expected 1H NMR spectra and were sufficiently pure as determined by combustion analysis. Analysis by triple detection GPC suggested that the small, dipolar diazopyruvyl endgroup of PEG-DAP 4 did not induce aggregation while the more hydrophobic hexyl nitroaryl azide of PEG-ANPAH 11 did have the propensity to aggregate. Photoactivated conjugation of both reagents was observed to occur with lysozyme, with indications that PEG-DAP 4 may produce a mono-PEG conjugate. Lysozyme conjugation with PEG-ANPAH 11 appeared to give conjugates with increasing number of conjugated PEG molecules. The conjugation of ribonuclease with PEG-DAP 4 was observed to give fewer multi-PEG species while the mono-conjugate was produced.

Effect of pH, temperature and sodium bisulfite or cysteine on the level of Maillard-based conjugation of lysozyme with dextran, galactomannan and mannan

The antimicrobial activity of lysozyme against Gram positive bacteria is well known. Application of this enzyme as a natural antimicrobial or preservative agent in food and pharmaceutical industry is under consideration in many laboratories. The antimicrobial effect of lysozyme can be extended towards Gram negative bacteria by chemical modification including conjugation with carbohydrates. The purpose of this investigation was to find the optimum experimental conditions for glycation of lysozyme with polysaccharides dextran, galactomannan and mannan and to evaluate some functional properties of the modified enzyme. Lysozyme was allowed to react with dextran under Maillard reaction condition at different pH and temperatures and in the presence of 50 mmol/L sodium bisulfite or cysteine and the extent of glycation was determined by ion exchange chromatography and SDS-PAGE. The optimum condition for glycation was pH 8.5 and 60 °C with a protein to derxtran molar ratio of 1:5. Same results were obtained for galactomannan but mannan did not react. Under these condition three moles dextran was attached to one mole lysozyme. Sodium bisulfite inhibited glycation at pH 8.5 and temperatures above 40 °C while cysteine prevented glycation at all pH and temperatures. Dextran-conjugated lysozyme exhibited improved heat stability, pH and heat solubility and better emulsifying property as compared with the unmodified lysozyme. These results suggest that it is possible to improve the properties of this enzyme in order to make it more suitable for application in foods and pharmaceuticals.

Use of Defined Estrone Glucuronide–Hen Egg White Lysozyme Conjugates as Signal Generators in Homogeneous Enzyme Immunoassays for Urinary Estrone Glucuronide

Three structurally characterized estrone glucuronide–lysozyme conjugates, E1 (a 60:40 mixture acylated at K3 and K97), E3 (acylated at K33), and E5 (acylated at both K33 and K97) were isolated and purified using a combination of cation-exchange chromatography on S-sepaharose in 7 M urea and hydrophobic interaction chromatography on butyl sepharose. Urea was essential to separate the conjugates into six chromatographically homogeneous fractions. In the absence of urea, complex mixtures of lysozyme and the six conjugate fractions were always encountered. The E1, E3, and E5 conjugates were highly inhibited by a sheep polyclonal anti-estrone glucuronide antibody only after the hydrophobic interaction chromatography step. The high level of inhibition enabled all three conjugates to be utilized as signal generators in homogenous enzyme immunoassays for urinary estrone glucuronide. Despite the apparently higher affinity of E3 for the antibody, both E1 and E3 gave standard curves that were indistinguishable provided that 1.7-fold more antiserum was used for E1. Both E1 and E3 yielded menstrual cycle urinary data that agreed with that provided by the Ovarian Monitor pre-coated assay tubes. Although, the menstrual cycle pattern was similar for the three signal generators, the E1G excretion rates yielded by E5 as the signal generator were only 60% of the reference values. Despite structural differences, there was no advantage gained in separating E1 and E3, but higher substituted conjugates such as E5 need removal for best assay performance.

Emulsifying properties and bactericidal action of chitosan–lysozyme conjugates

The solubility of chitosan was greatly improved by conjugation with lysozyme through Maillard-type protein–polysaccharide reaction. The emulsifying properties, especially emulsion stability, were improved by lysozyme–chitosan conjugation. The improvement in emulsifying properties was better in the conjugates of high molecular weight-type chitosan (HMC) than low molecular-type chitosan (LMC). The lysozyme–HMC conjugate has greatly improved emulsion stability at acidic pH. The conjugates have greatly enhanced bactericidal action against Escherichia coil K-12, a typical Gram-negative bacterium. Although the bactericidal activity of LMC was much lower than that of HMC, it was improved by conjugation with lysozyme. Thus, chitosan–lysozyme conjugate can be used as a new functional ingredient having excellent emulsifying properties and bactericidal action.

Characterization of lysozyme-estrone glucuronide conjugates. The effect of the coupling reagent on the substitution level and sites of acylation.

Estrone glucuronide conjugates of hen egg white lysozyme were prepared by the mixed anhydride and active ester coupling procedures. Both methods gave good yields of conjugates, but the active ester procedure gave a more diverse range of products, making it less suitable for preparing conjugates for homogeneous enzyme immunoassay. Conjugation of lysozyme with estrone glucuronide by the mixed anhydride procedure gave one major derivative exclusively acylated at lysine residue 33 whereas conjugation by the active ester method gave six derivatives which were acylated at one or more of lysine residues 33, 97, and 116. None of the lysine residues 1, 13, and 96, or the N-terminal alpha-amino group, were acylated in any of the conjugates isolated. The correlation of the conjugate structures with the protein environments of the amino groups in the crystal structure of lysozyme suggested that the sites of acylation were determined not only by the chemical nature of the acylating reagent but also by the surface accessibility and nucleophilicity of the individual lysine residues.

A novel family of ubiquitin-specific proteases in chick skeletal muscle with distinct N- and C-terminal extensions.

We have recently identified a cDNA for a ubiquitin-specific protease (UBP), UBP41, that encodes the smallest functional UBP identified to date, using an Escherichia coli-based in vivo screening method. In the present study we isolated highly related cDNAs encoding a new family of UBP enzymes, named UBP46, UBP52 and UBP66. These UBPs have virtually identical catalytic domains spanning the sequence of UBP41 between the active-site Cys and the His box (95% identity). However, they possess distinct N- and/or C-terminal extensions. Moreover, they are more closely related to each other than to any other members of the UBP family. Thus these chick UBPs must define a novel family of de-ubiquitinating enzymes and should represent the first example among the UBP family enzymes, whose multiplicity is achieved by variation in their N- and C-terminal extensions. The chick UBPs were expressed in E. coli, and purified from the cells to apparent homogeneity using 125I-labelled ubiquitin-alphaNH-MHISPPEPESEEEEEHYC as a substrate. Each of the purified UBP46, UBP52 and UBP66 enzymes behaved as proteins of similar sizes under both denaturing and non-denaturing conditions, suggesting that all of them consist of a single polypeptide chain. The UBP enzymes cleaved the C-terminus of the ubiquitin moiety in natural and engineered fusions irrespective of their sizes and thus are active against ubiquitin-beta-galactosidase as well as a ubiquitin C-terminal extension protein of 80 amino acids. All UBPs except UBP66 released free ubiquitin from poly-His-tagged di-ubiquitin. However, the isopeptidase activity for hydrolysing polyubiquitinated lysozyme conjugates was not detected from these UBPs, which makes these UBPs distinct from UBP41. These results suggest that the chick UBPs may play an important role in production of free ubiquitin from linear polyubiquitin chains and of certain ribosomal proteins from ubiquitin fusion proteins.

Drug Delivery to the Kidneys and the Bladder with the Low Molecular Weight Protein Lysozyme

The low molecular weight protein (LMWP) lysozyme is a suitable drug carrier for renal drug targeting. When the tubular reabsorption of a LMWP can be prevented, the protein will be excreted in the urine. In this way, lysozyme (LZM) conjugates might also be used as carriers for targeting to the urinary tract. Since positive domains on the protein surface are important for the interaction with the tubular uptake-receptor, we studied the urinary excretion of a drug-LZM conjugate with and without positive charge on the LMWP. We synthesized two conjugates with the fluorescent compound fluorescein. A positively charged conjugate was obtained by reacting fluorescein isothiocyanate (FITC) with LZM at a 1:1 molar to molar ratio; this conjugate contained six free primary aminogroups. The conjugate without positively charged groups was obtained by reacting the remaining free primary aminogroups of the FITC-LZM with succinic anhydride (Suc). The Suc-FITC-LZM contained only 0.2 free primary amino-groups per molecule. We studied the pharmucokinetics of the conjugates in freely moving Wistar rats. The FITC-LZM conjugate was excreted intactly into the urine for 29 ± 4% of the injected dose. The Suc-FITC-LZM was excreted into the urine intactly for 45 ± 4%. These data indicate that the excretion of a drug-LAMP conjugate into the urine can be increased by decreasing the positive charge on the carrier surface. Such a carrier may be an attractive candidate for drug targeting to the bladder.

Drug-targeting to the kidney: Renal delivery and degradation of a naproxen-lysozyme conjugate in vivo

A renal-specific controlled release of an active drug may enable a reduction of the required dose and may provide a reduction of extra-renal toxicity. To achieve renal specific targeting of the NSAID naproxen, the low-molecular-weight protein (LMWP) lysozyme was employed as carrier since it is mainly taken up and catabolized in the proximal tubules of the kidney. A conjugate was synthesized with an average coupling degree of 2 mol naproxen per 1 mol lysozyme in which the drug was directly coupled to the protein via a peptide bond. First, we investigated whether naproxen conjugation affects the renal disposition of lysozyme. As native lysozyme, the conjugate was predominantly and rapidly (within 20 min) taken up by the kidney. The subsequent decrease in renal content reflecting the renal degradation of the conjugated lysozyme molecules appeared also to be similar to that of native lysozyme with a half life of four hours. Second, the effect of lysozyme conjugation on the body distribution of naproxen was studied. An important observation with regard to the aimed reduction in extra-renal side effects was that no detectable amounts of free naproxen were present in the plasma after administration of conjugate. Conjugation of naproxen to lysozyme resulted in a pronounced (70-fold) increase of naproxen accumulation in the kidney. In agreement with the protein disposition study, the conjugate was rapidly taken up by the kidney and subsequently degraded. In conclusion, renal selective targeting of the NSAID naproxen can be obtained by conjugation with the LMWP lysozyme. This concept of drug delivery to the kidney has the potential to improve drug efficacy and safety.

Molecular Cloning of a Novel Ubiquitin-specific Protease, UBP41, with Isopeptidase Activity in Chick Skeletal Muscle

A cDNA encoding a new ubiquitin-specific protease, UBP41, in chick skeletal muscle was cloned using an Escherichia coli-based in vivo screening method. Nucleotide sequence analysis of the cDNA containing an open reading frame of 1,071 base pairs revealed that the protease consists of 357 residues with a calculated molecular mass of 40,847 Da, and is related to members of the UBP family containing highly conserved Cys and His domains. Chick UBP41 was expressed in E. coli and purified from the cells to apparent homogeneity, using 125I-labeled ubiquitin-alphaNH-MHISPPEPESEEEEEHYC as a substrate. The purified enzyme behaved as an approximately 43-kDa protein under both denaturing and nondenaturing conditions, suggesting that it consists of a single polypeptide chain. Like other deubiquitinating enzymes, it was sensitive to inhibition by ubiquitin-aldehyde and sulfhydryl blocking agents, such as N-ethylmaleimide. The UBP41 protease cleaved at the C terminus of the ubiquitin moiety in natural and engineered fusions irrespective of their sizes; thus, it is active against ubiquitin-beta-galactosidase as well as ubiquitin C-terminal extension protein of 80 amino acids. UBP41 also released free ubiquitin from poly-His-tagged di-ubiquitin. Moreover, it converted poly-ubiquitinated lysozyme conjugates to mono-ubiquitinated forms of about 24 kDa, although the latter molecules were not further degraded to free ubiquitin and lysozyme. These results suggest that UBP41 may play an important role in the recycling of ubiquitin by hydrolysis of branched poly-ubiquitin chains generated by the action of 26 S proteasome on poly-ubiquitinated protein substrates, as well as in the production of free ubiquitin from linear poly-ubiquitin chains and of certain ribosomal proteins from ubiquitin fusion proteins.

Effects of nucleotides on assembly of the 26S proteasome and degradation of ubiquitin conjugates.

We have investigated three aspects of nucleotide usage by the 26S proteasome and its regulatory complex (RC). Both particles hydrolyze the four major ribonucleotides, but ATP and CTP have substantially lower Kms for hydrolysis than do GTP and UTP. The Km for ATP hydrolysis is 15 microm for the 26S proteasome and 30 microm for the regulatory complex. Formation of the 26S proteasome from the RC and the 20S proteasome requires about 5 microm ATP. Although measurable degradation of Ubiquitin(Ub)-lysozyme conjugates occurs in the presence of CTP, GTP, and UTP, the best nucleotide for Ub-conjugate degradation by the 26S proteasome is ATP, with an estimated Km of 12 microm. In summary, our studies show that micromolar concentrations of ATP are sufficient for several 26S proteasome activities.

Characteristics of 26 S Proteases from Fission Yeast Mutants, which Arrest in Mitosis

We have isolated the 26 S protease from the fission yeast Schizosaccharomyces pombe. The affinity-purified enzyme contains the two regulatory ATPases mts2 +, a homolog of human S4, and CIM5, a homolog of human MSS1=S7. We show that mts3 +, a homolog of the budding yeast NIN1 protein and human S14, is a true component of the 19 S regulatory complex from the fission yeast. The 26 S proteases purified from two thermosensitive mutants, mts2-1 and mts3-1, which arrest in cell cycle at the restrictive temperature (37°C), have been compared with the wild-type enzyme after growing cells at permissive (25°C) and non-permissive temperatures. We demonstrate that mutated mts2 protein is integrated into the protease complex prepared from mts2 cells, whereas mutated mts3 is not present in the 19 S regulatory complex from mts3 cells. The two mutant 26 S proteases isolated after growing cells at 37°C remain stable for two hours at 37°C as measured by ATP-dependent cleavage of the fluorogenic peptide sucLLVY-MCA. At the restrictive temperature, the mutant 26 S proteases do not degrade ubiquitin-[ 125I]lysozyme conjugates in an ATP-dependent manner, indicat ing that mts2 +and mts3 +are essential for ubiquitin conjugate degradation. This explains the conditional lethality of the mutants and the cell-cycle arrest in metaphase to anaphase transition. In addition, our data demonstrate that the ATPases of the 26 S enzyme are not redundant.

Protective effect of lysozyme-galactomannan or lysozyme-palmitic acid conjugates against Edwardsiella tarda infection in carp, Cyprinus carpio L.

The protective effect of lysozyme-galactomannan or lysozyme-palmitic acid conjugates orally administered to carp, Cyprinus carpio L. was investigated using a virulent strain of Gram-negative Edwardsiella tarda isolated from an infected fish. Lysozyme-galactomannan conjugate was prepared through controlled Maillard reaction. Lysozyme-palmitic acid conjugate was prepared through base-catalyzed ester exchange using N-hydroxysuccinimide ester of palmitic acid. The conjugates provided substantial protection to carp infected with a Gram-negative bacteria fish pathogen E. tarda NG 8104. Lytic activities of lysozyme conjugates with galactomannan and palmitic acid were about 80 and 71% of native lysozyme using Micrococcus lysodeikticus as a substrate. Feeding with lysozyme conjugates, for 8 days, significantly enhanced fish protection against E. tarda infection. The survival rate was 30% for lysozyme-galactomannan conjugate treated fish and 20% for lysozyme-palmitic acid conjugate treated fish after 6 days cultivation while all control fish died within 3 days. On the other hand, a recovery rate of 40% after 6 days was observed in the fish group that were fed lysozyme-palmitic acid conjugate 3 and 2 h before and after E. tarda challenge, respectively, and for 6 consecutive days. The results of this work show the possibility of utilizing lysozyme conjugates with galactomannan or palmitic acid as a therapeutic for infection in fish.

Inhibitory Effect of Nonenzymatic Glycation on Ubiquitination and Ubiquitin-Mediated Degradation of Lysozyme

We examined ubiquitination and ubiquitin-mediated degradation of glycated protein by rabbit reticulocyte lysate fraction II (ubiquitin-free preparation). Non-glycated lysozyme and three glycated lysozyme preparations with different glucose binding ratios were used as substrates. Glycation sites of the Iysozyme were mostly the ϵ-NH 2 group of lysine residues, since modification at the α-NH 2 group of the amino terminal was not detectable. Ubiquitin was conjugated with three glycated lysozyme preparations, which contained 1.4, 2.8 and 4.5 mol glucose per mol, by fraction II supplemented with hemin. The extent of formed conjugates was reduced 81, 72 and 56% of those of ubiquitin-non-glycated lysozyme conjugates, respectively. Additionally, ubiquitin-mediated degradation of the resultant conjugates was reduced and their respective rates were 97, 56 and 19% of that of the non-glycated lysozyme. These results indicated that both ubiquitin conjugation and ubiquitin-mediated degradation of the lysozyme were inhibited by nonenzymatic glucose binding to the lysozyme.

Ubiquitin C-terminal hydrolase activity associated with the 26 S protease complex.

In the ubiquitin (Ub) system for protein degradation, proteins ligated to Ub are degraded by an ATP-dependent 26 S protease complex. During or after proteolysis, free Ub is regenerated, but the mechanisms of Ub release remained unknown. It was previously observed that free Ub is released from a Ub-histone conjugate by an ATP-dependent activity present in partially purified preparations of 26 S complex, but the relationship of this activity to protein breakdown was not established. We now show that purified preparations of 26 S complex release free Ub from conjugates that are good substrates for proteolysis, such as conjugates of lysozyme with reductively methylated Ub. The activity that releases free Ub co-migrates with the 26 S protease complex in glycerol density gradient centrifugation, indicating that the responsible Ub C-terminal hydrolase is an integral part of the 26 S complex. Complex-associated hydrolase can also act on adducts in which a single Ub unit is attached to protein, such as a bacterially expressed construct in which the C terminus of Ub is fused to the alpha-NH2 group of a fragment of Ub that contains 60% of its N-terminal region. In all cases, Ub release is insensitive to Ub-aldehyde (an inhibitor of some Ub C-terminal hydrolases) and is stimulated by MgATP. ATP cannot be replaced by beta, gamma-nonhydrolyzable analogs, but it can be substituted by CTP and GTP. The nucleotide specificity of Ub release by the 26 S complex is similar to that observed previously for conjugate proteolysis and nucleotide hydrolysis. It thus seems that the activity of the Ub C-terminal hydrolase associated with the 26 S complex is tightly coupled to the proteolytic action of the complex, and it may have a role in the release of Ub from linkage to amino groups of the protein substrate at the final stages of the Ub proteolytic pathway.

Constraints in antigen processing result in unresponsiveness to a T cell epitope of hen egg lysozyme in C57BL/6 mice.

T cell hybridoma clones were derived after fusion of BW-5147 parent cells with lymphocytes from C57BL/6 mice injected with phosphorylcholine (PC)-hen egg lysozyme (HEL) conjugates. Several T cell hybridomas were preferentially reactive with PC-HEL over unconjugated HEL, and a particular clone (PC-H4.1) was further analyzed. This T cell hybridoma clone could respond to its maximal level toward unconjugated HEL only when the dose of HEL was increased to 5-10-fold of the PC-HEL concentration. Interestingly, this clone was not stimulated by unfolded HEL (by S-carboxymethylation) to the level of PC-HEL. A synthetic peptide representing the amino acid position 47-61 of HEL, which is known to be non-immunogenic upon HEL injection in C57BL/6 mice, was able to stimulate the hybridoma only to a level comparable to that induced by unconjugated HEL. The T cell response to this synthetic peptide required an additional antigen-processing step, based on its inability to stimulate T cells after treatment of antigen-presenting cells with leupeptin, chloroquine or paraformaldehyde. Deletion of a single C-terminal amino acid residue of HEL 47-61 (arginine) significantly enhanced (10-100-fold of HEL 47-61) the T cell reactivity and abrogated the necessity of further antigen processing. These results suggest that the lack of a T cell response to a certain epitope may not be due to the lack of a T cell repertoire reactive to the epitope. In some cases, the unresponsiveness may be due to the difficulty in generating the particular epitopes. Taken together, modification of the lysozyme molecule with PC conjugation may facilitate further antigen processing of HEL to generate an optimal epitope for the nonresponder mice.

Multicatalytic and 26 S ubiquitin/ATP-stimulated proteases in maturing rabbit red blood cells

Rabbit red blood cells of various ages were separated on Percoll gradients and the activities of two large cytosolic proteases were measured. Both the multicatalytic protease (MCP), assayed by hydrolysis of fluorigenic peptides, and the 26 S ubiquitin/ATP-stimulated protease, assayed by degradation of ubiquitin—lysozyme conjugates, declined 3-fold or less during maturation of rabbit reticulocytes to erythrocytes. The ability of MCP to hydrolyze three classes of peptides decreased in parallel indicating that the 20 S protease is not significantly remodeled during red blood cell maturation.

Specific disulfide cleavage is required for ubiquitin conjugation and degradation of lysozyme.

Both ubiquitin conjugation and ubiquitin-dependent degradation of chicken egg white lysozyme in a reticulocyte lysate depend on the presence of a reducing agent. We present evidence that the reduction of a specific disulfide bond, namely that at Cys6-Cys127, facilitates ubiquitination and is a prerequisite to the formation of a multiubiquitin chain on one of at least four chain initiation sites on lysozyme. The Cys6-Cys127 disulfide bond in lysozyme can be specifically reduced, and the modified protein can be isolated after carboxymethylation of the 2 resulting cysteines. This modified lysozyme no longer requires the presence of a reducing agent for ubiquitin conjugation and degradation. Inhibition of ubiquitination by the dipeptide Lys-Ala revealed that this modified lysozyme, like the unmodified protein, is recognized via the binding of the ubiquitin protein ligase, E3, to the substrate's N-terminal lysyl residue. Both the rate and the extent of ubiquitin-lysozyme conjugation, however, are significantly higher with this modified substrate. Likewise, ubiquitin-dependent degradation of 6,127-reduced/carboxymethylated lysozyme was 2-4-fold faster than degradation of the unmodified counterpart. These results are consistent with an interpretation that the modified lysozyme mimics an intermediate formed at the rate-limiting step of the degradation of lysozyme in the reticulocyte lysate. Reduction of the Cys6-Cys127 disulfide bond is expected to unhinge the N-terminal region of lysozyme, and we propose that the recognition of this otherwise stable protein by the ubiquitin pathway is due to facilitated binding of E3 that results from such a conformational transition.

Home monitoring of gonadotropin ovulation induction using the Ovarian Monitor

The safe use of gonadotropins relies on close hormonal and/or ultrasound monitoring to assess the response to treatment, requiring multiple hospital visits. Home monitoring with the Ovarian Monitor (St. Michael Research Foundation, Macleod, Victoria, Australia) minimizes hospital visits and overcomes many of the logistic difficulties associated with gonadotropin use. It utilizes a system of homogenous enzyme immunoassay using lysozyme conjugates to measure quantitatively either urinary estrone-3 or pregnanediol-3-glucuronide. Results obtained by 24 patients in 57 cycles using the Ovarian Monitor at home correlate closely with results obtained in the laboratory (estrone-3-glucuronide r = 0.955; pregnanediol-3-glucuronide r = 0.958). Cycle outcomes (ovulation, 74%/cycle; clinical pregnancy, 30%/cycle; multiple pregnancy, 13%/pregnancy; hyperstimulation, 11%/cycle) are no different from those achieved in laboratory-monitored patients. Home monitoring can be as safe and effective as laboratory monitoring, offers significant social benefits, and improves access to this form of therapy.