The role of an invariant tryptophan residue in alpha-bungarotoxin and cobrotoxin. Investigation of active derivatives with the invariant tryptophan replaced by kynurenine

Ozone oxidation converted the single, invariant, tryptophan residue to N2-formylkynurenine in alpha-bungarotoxin and cobrotoxin. Upon this modification, the lethal toxicity was significantly reduced in cobrotoxin but mostly retained in alpha-bungarotoxin. Each neurotoxin containing kynurenine instead of tryptophan retained the same antigenicity as the native toxin. Fluorescence and CD spectroscopy revealed that, although the environment and state of the kynurenine residue were similar, [Kyn29]cobrotoxin was much more sensitive to pH change than alpha-[Kyn28]bungarotoxin. In terms of lethal toxicity and conformational stability, the invariant tryptophan residue appears to play a more important role in cobrotoxin, imparting a higher lethal toxicity than that in alpha-bungarotoxin, which has a disulfide bond at Cys29-Cys33.     

Role of arginine and histidine residues in the biological activity of botulinic neurotoxin A

Treatment of botulinic neurotoxin A with cyclohexanedione demonstrated that modification of 5 to 10 arginine residues does not change the neurotoxin toxicity, while after modification of 15-20 arginine residues the toxicity is decreased by 40-50% of the original value. Butanedione exerts a stronger detoxicating effect on neurotoxin than cyclohexanedione. The molecular conformation of the modified toxin derivatives and their precipitability upon interaction with antisera against toxin and toxin fragments does not change thereby. The non-toxic derivatives of toxin containing 40 modified arginine residues possess a partial serological affinity for the original toxin in a reaction with antiserum against toxin but do not interact with the antifragment sera. The molecular conformation of these preparations is changed considerably. It is assumed that one or two arginine residues are located near the toxic site of the neurotoxin molecule and are also components of its antigenic determinants. Modification of histidine residues in the neurotoxin molecule by diethylpyrocarbonate is accompanied by a decrease of its toxicity. An additional 10% toxicity is revealed upon modification of 11-13 histidine residues. The molecular conformation of the modified derivatives of neurotoxin and their precipitability do not change thereby. It is probable that 1 or 2 histidine residues are located at or near the toxic site. The data obtained suggest that histidine residues are not localized in antigenic determinants of the neurotoxin molecule.     

Structure and action of heteronemertine polypeptide toxins: Inactivation of Cerebratulus lacteus toxin B-IV concomitant with tryptophan alkylation

Reaction of Cerebratulus lacteus toxin B-IV with 2-hydroxy-5-nitrobenzyl bromide at pH 4.5 results in modification of toxin tryptophan residues and loss of biological activity. With relatively small reagent excesses, one tryptophan per molecule is modified without major effect on toxicity. Further reaction results in modification of a second residue of tryptophan and loss of at least 95% of the toxic activity. Modification of one or both tryptophan residues is without significant effect on the secondary structure of the protein. The specificity of each phase of the reaction has been assessed by fingerprint analysis of peptides derived from toxin modified to differing extents with 2-hydroxy-5-nitrobenzyl bromide. It is thus possible to show that tryptophan-5 reacts first and tryptophan-30 only under more rigorous conditions. It thus appears that tryptophan-30 is essential for full neurotoxic activity.     

Chemical modification of the tryptophan residue in adrenocorticotropin.

The single tryptophan residue in the pituitary hormone adrenocorticotropin was modified selectively by reaction with a variety of substituted o-nitrophenylsulfenyl chlorides. In addition to quantitative modification of the tryptophan residue, the reaction invariably resulted in partial oxidation of the methionine residue to the sulfoxide. The methionine sulfoxide derivative could be separated from the desired product by partition chromatography on Sephadex G-50 in the solvent system 1-butanol-pyridine-0.1% acetic acid (5:3:11). Thus, the 2,4-dinitrophenylsulfenyl, 2-nitro-4-carboxyphenylsulfenyl, and 2-nitro-4-carbamidophenylsulfenyl derivatives of adrenocorticotropin were prepared and characterized. Modifications in the isolation of adrenocorticotropin from ovine pituitaries are also described. The melanocyte stimulating activities of the native hormone and the analogues are discussed.     

Antigenic Reactivities of Chemically Modified β-Lactoglobulins with Antiserum to Bovine β-Lactoglobulin

Analysis of the quantitative precipitation of bovine β-lactoglobulin (β-Lg) with rabbit antiserum to β-Lg indicated that there were at least four antigenic sites on β-Lg. To study the antigenic property of bovine β-Lg, we examined the antigenic reactivity of anti β-Lg serum with β-Lg specifically modified with chemical reagents by immunodiffusion analysis, a quantitative precipitin test, and an enzyme-linked immunosorbent assay.

Modification of arginine residues, tryptophan residues, or sulfhydryl groups had little effect on the antigenic reactivity. A significant decrease in the reactivity was observed when β-Lg was acetylated, succinylated, modified with diethylpyrocarbonate or coupled with glycine amide.

These results suggest that 1.1 of three arginine residues, two tryptophan residues, and one sulfhydryl group are out of the antigenic sites, but there is a possibility that the amino group, histidine residue and carboxyl group may play an important role in the antigenicity of bovine β-Lg.     

Kinetics and Mechanism of St I Modification by Peroxyl Radicals

St I is a toxin present in the Caribbean Sea anemone Stichodactyla helianthus which is highly hemolytic in the nanomolar concentration range. Exposure of the toxin to free radicals produced in the pyrolysis of 2,2-azobis(2-amidinopropane) hydrochloride leads to a progressive loss of hemolytic activity. This loss of hemolytic activity is accompanied by extensive modification of tryptophan residues. On the average, three tryptophan residues are modified by each inactivated toxin. The loss of hemolytic activity of St I takes place without significant changes in the protein structure, as evidenced by the similarity of the fluorescence and CD spectra of native and modified proteins. Also, the native and modified ensembles present a similar resistance to their denaturation by guanidinium chloride. The hemolytic behavior and the performance of the toxin at the single-channel level when incorporated to black lipid membranes suggest that the modified ensemble can be considered as composed of inactive toxins and active toxins whose behavior is similar to that of the native proteins. These results, together with the lack of induction time in the activity loss, suggest that the fall of hemolytic activity takes place by an all-or-nothing inactivation mechanism in which the molecules become inactive when a critical amino acid residue is modified.     

Observations on the reaction of 2-hydroxy-5-nitrobenzyl bromide with a peptide-bound tryptophanyl residue

Previous studies on the isolation of peptides containing tryptophanyl residues modified with 2-hydroxy-5-nitrobenzyl bromide demonstrated multiple products of reaction at the same residue as well as technical difficulties in the primary structure analysis of peptides containing the modified tryptophanyl residue. The present study was undertaken to explore the reaction of 2-hydroxy-5-nitrobenzyl bromide with the single tryptophanyl residue in a synthetic peptide, experimental allergenic encephalitogenic peptide. The modification of this peptide was accomplished in sodium acetate, pH 4.75, and reagent removed by gel filtration. Amino acid analysis of the modified peptide suggested that only the tryptophanyl residue had been modified under these experimental conditions. The modified peptide could be separated into multiple derivatives by high-performance liquid chromatography. Although it is clear that some of the observed heterogeneity reflects a difference in the degree of substitution at the single tryptophanyl residue, several of the derivatives appear to have the same extent of substitution. It is suggested that the heterogeneity observed is a reflection of the establishment of a new diastereoisomeric center in the peptide. These results are consistent with previous observations from other laboratories and provide a basis for the explanation of apparent heterogeneity of peptides obtained from modified proteins.     

Nitrated and oxidized products of a single tryptophan residue in human Cu,Zn-superoxide dismutase treated with either peroxynitrite-carbon dioxide or myeloperoxidase-hydrogen peroxide-nitrite

We reported previously that a single tryptophan residue, Trp32, in human Cu,Zn-superoxide dismutase is specifically modified by peroxynitrite-CO2 [Yamakura et al. (2001) Biochim. Biophys. Acta 1548, 38-46]. In this study, we modified Cu,Zn-superoxide dismutase by using a combination of myeloperoxidase, hydrogen peroxide, and nitrite. The modified enzyme showed no loss of copper and zinc, and 15% less enzymatic activity. Trp32 was the only significant amino acid lost. After trypsin digestion of the modified SOD with peroxynitrite-CO2 and the myeloperoxidase system, six newly appearing peptides containing tryptophan derivatives were observed on microLC-ESI-Q-TOF mass analyses and HPLC with a photodiode-array detector. The derivatives of the tryptophan residue exhibiting mass increases of 4, 16 (2 peaks), 32, 45 (major), and 45 Da (minor) were identified as kynurenine, oxindole-3-alanine and its derivatives, dihydroxytryptophan, 6-nitrotryptophan and 5-nitrotryptophan, respectively. We further identified 6-nitrotryptophan from the 1H-NMR spectrum for the pronase-digested product and calculated the yield of 6-nitrotryptophan as being about 30% for each of the modification methods. The tryptophan residue in the modified human Cu,Zn-superoxide dismutase gave the same spectra for the products including 6-nitrotryptophan as the major nitrated product with the two different modification systems.     

The purification and characterization of a necrotoxin from tarantula, Dugesiella hentzi (Girard), venom

The major toxin, a necrotoxin, of the venom of Dugesiella hentzi (Girard) has been purified by gel filtration. The purified toxin was homogeneous by gel filtration, polyacrylamide gel electrophoresis, and an isoelectric focusing procedure. The molecular weight estimation was 6700 and the isoelectric pH was 10.0. The amino acid composition shows 16 lysine, 8 cysteine, and one tryptophan residues, with no tyrosine, methionine, alanine, arginine, or histidine residues. The purified protein is toxic to certain insects and mice with the primary site of action being muscle tissue in the mouse. Modification of the single tryptophan residue resulted in a loss of toxicity.A significant increase of serum creatine phosphokinase activity was observed in mice injected with the necrotoxin. Histological examination showed the primary lesions were acute focal areas of myocardial necrosis, and no histological differences in myocardial lesions were seen between mice injected with the purified necrotoxin or with the whole venom.     

Chemical modification of ribonuclease T1 with ozone.

The single tryptophan residue in ribonuclease T1 [EC 3.1.4.8] was selectively oxidized by ozone to N'-formylkynurenine, which was then converted to kynurenine by acid-catalyzed deformylation in the frozen state. The two enzyme derivatives thus formed, NFK- and Kyn-RNase T1, lost enzymatic activity at pH 7.5, at which native RNase T1 most efficiently catalyzes the hydrolysis of RNA. At pH 4.75, the modified enzymes retained a decreased but distinct enzymatic activity toward RNA without alteration of substrate specificity, and Kyn-RNase T1 was four times more active than NFK-RNase T1. The binding of 3'-GMP to these modified enzymes decreased remarkably at pH 5.5, the optimum pH for binding to the intact enzyme. The gamma-carboxyl group of glutamic acid 58 was still reactive to iodoacetic acid after modification of tryptophan 59. The amounts of the carboxymethyl group introduced into NFK- and Kyn-RNase T1 were 0.36 and 0.59 mol, respectively, under conditions such that quantitative esterification of native RNase T1 takes place. CD spectroscopy indicated that the tertiary structure of the molecule was disordered in NFK-RNase T1, but not significantly in Kyn-RNase T1. It is concluded that tryptophan 59 functions in maintaining the active conformation of the protein structure, particularly in constructing the active environment for a functionally important set of groups involved in the binding of the substrate at the active site, although direct participation of in tryptophan the catalytic function of ribonuclease T1 is unlikely.     

Identification of the tryptophan residue located at the low-affinity saccharide binding site of ricin D

The saccharide binding ability of the low affinity (LA-) binding site of ricin D was abrogated by N-bromosuccinimide (NBS)-oxidation, while in the presence of lactose the number of tryptophan residues eventually oxidized decreased by 1 mol/mol and the saccharide binding ability was retained (Hatakeyama et al., (1986) J. Biochem. 99, 1049-1056). Based on these findings, the tryptophan residue located at the LA-binding site of ricin D was identified. Two derivatives of ricin D which were modified with NBS in the presence and absence of lactose were separated into their constituent polypeptide chains (A- and B-chains), respectively. The modified tryptophan residue or residues was/were found to be contained in the B-chain, but not in the A-chain. From lysylendopeptidase and chymotryptic digests, peptides containing oxidized tryptophan residues were isolated by gel filtration on Bio-Gel P-30 and HPLC. Analysis of the peptides containing oxidized tryptophan revealed that three tryptophan residues at positions 37, 93, and 160 on the B-chain were oxidized in the inactive derivative of ricin D, in which the saccharide binding ability of the LA-binding site was abrogated by NBS-oxidation. On the other hand, the modified residues were determined to be tryptophans at positions 93 and 160 in the active derivative of ricin D which was modified in the presence of lactose, indicating that upon binding with lactose, the tryptophan residue at position 37 of the B-chain was protected from NBS-oxidation. From these results, it is suggested that tryptophan at position 37 on the B-chain is the essential residue for saccharide binding at the LA-binding site of ricin D.     

Immunochemistry of sea anemone toxins: structure-antigenicity relationships and toxin-receptor interactions probed by antibodies specific for one antigenic region

Two antibody subpopulations directed against Anemonia sulcata toxin I or II have been purified by immunoaffinity chromatography. These antibodies are specific for a single antigenic region and were used in a structure-antigenicity relationship study using homologous toxins and chemically modified derivatives of A. sulcata toxin II. Asp-7 and/or Asp-9 and Gln-47 of toxin II were found to be implicated in the antigenic region recognized by the two antibody subpopulations. On the contrary, Arg-14, Lys-35, -36, and -46, and alpha-NH2 of the glycine residue of A. sulcata toxin II are not involved in the corresponding antigenic region. When assayed for interaction with the sodium channel, the antigenic region of toxin II, including Asp-9 and Gln-47, appeared fully accessible to its specific antibodies, suggesting that it is not involved in the binding of the toxin to its receptor.     

Enzymic and immunochemical properties of lysozyme. XVI. A novel synthetic approach to an antigenic reactive site by direct linkage of the relevant conformationally adjacent residues constituting the site.

Previous studies from this laboratory on the immunochemistry of specific chemical derivatives of native lysozyme and of the two disulfide peptide 62-68 (Cys 64-Cys 80) 74-97 (Cys 76-Cys 94) (i.e. (SS)2-peptide), have established an antigenic reactive site to comprise the spatially contiguous surface residues: Trp 72, Lys 97, Lys 96, Asn 93, Thr 89 and Asp 87. In the present work, the identity of the site was verified by an entirely different and novel approach. The aforementioned amino acids were linked directly into a single linear peptide with an intervening spacer where appropriate and substituting phenylalanine for tryptophan (i.e. Phe-Gly-Lys-Asn-Thr-Asp). This peptide (which does not exist in native lysozyme but simulates a surface region of the protein) possessed a remarkable inhibitory activity towards the reaction of lysozyme with its antisera. The immunochemical reactivity of the peptide was equal to the maximum expected reactivity of the site (i.e. a third of the total antigenic reactivity of lysozyme). These findings define quite conclusively and accurately the reactive site which is clearly composed of spatially adjacent residues that are distant in sequence reacting as if in direct linear linkage. The unequivocal establishment of this concept indicates that antigenic sites need not always be composed of residues in direct peptide linkage in the sequence. The nature of the site may depend on the protein. This unorthodox attack at the problem provides a novel and powerful approach for final delineation of the antigenic reactive sites (and perhaps other types of binding sites) in native proteins, following the completion of accurate narrowing down by chemical methods.     

Catalytic properties of tryptophanless recombinant horseradish peroxidase

Heme-containing plant peroxidases (EC 1.11.1.7) contain a highly conserved single tryptophan residue. Its replacement with Phe in recombinant horseradish peroxidase (rHRP) increased the stability of the mutant enzyme in acid media. The kinetic properties of native, wild-type, and W117F mutant recombinant horseradish peroxidase in the reactions of ammonium 2, 2;-azino-bis(3-ethylbenzthiazoline-6-sulfonate) (ABTS), guaiacol, and o-phenylenediamine oxidation are very similar. However, significant changes in the reaction rate constant characteristic for the monomolecular rate-limiting step ascribed either to product dissociation from its complex with the enzyme or electron transfer from the substrate to the active site within the Michaelis complex were observed. The data indirectly indicate the participation of the single Trp residue in oxidation of ABTS and guaiacol and possible differences in kinetic mechanisms for oxidation of ABTS, guaiacol, and o-phenylenediamine.     

Structural analysis of staphylococcal enterotoxins B and C1 using circular dichroism and fluorescence spectroscopy

Secondary and tertiary structural parameters of two functionally and serologically related proteins, staphylococcal enterotoxins B and C1, have been determined by using circular dichroism and fluorescence spectroscopy. The secondary structures derived from the respective far-UV circular dichroic spectra were 9.5% alpha-helix, 55.0% beta-pleated sheets, 16.5% beta-turns, and 19.0% random coils for enterotoxin B and 15.0% alpha-helix, 38.0% beta-pleated sheets, 25.5% beta-turns, and 21.5% random coils for staphylococcal enterotoxin C1. The values matched well with the secondary structures derived from the amino acid sequences (Chou and Fasman method). Seven antigenic sites have been predicted for both staphylococcal enterotoxins B and C1 by using the hydrophilicity and the secondary structure information. Three of these antigenic sites appear similar. Fluorescence quantum yield of the single tryptophan residue (Trp-197) of both the enterotoxins showed the tryptophan residue in staphylococcal enterotoxin B to be approximately 46% more fluorescent than in staphylococcal enterotoxin C1. Tryptophan fluorescence quenching by the surface quencher I- and the neutral quencher acrylamide revealed that the single tryptophan residue in each of the enterotoxins is buried in the protein matrix and is not accessible to the surface quencher I-. The tryptophan residue in staphylococcal enterotoxin C1 is 14% less accessible to acrylamide than in staphylococcal enterotoxin B. The data, in general, reflect several similarities and significant differences between the two related enterotoxins.     

The role of tryptophan in structural and functional properties of equinatoxin II.

A pore-forming, cytolytic and lethal polypeptide, equinatoxin II, from the sea anemone Actinia equina, was subjected to oxidation with N-bromosuccinimide to study the role of five present tryptophan residues in structure-function relationships. In the folded toxin molecule, 1-2 tryptophan residues were readily susceptible to oxidation with N-bromosuccinimide, whereas modification of a single residue resulted in complete impairment of the toxin lethal and hemolytic activities as well as the ability of an oxidized toxin to precipitate with serum lipoproteins. CD and fluorescence spectra indicated a slight alteration of a toxin secondary structure following N-bromosuccinimide treatment. Incubation with sphingomyelin of the toxin prior to oxidation did not prevent subsequent modification with N-bromosuccinimide and loss of its activities, indicating that the modified tryptophan residue is not directly involved in toxin binding and insertion into lipid membranes. It was concluded that the modified tryptophan residue is essential for the structure of equinatoxin II.     

On the molecular mechanisms of neutralization of a cobra neurotoxin by specific antibodies

Examination of 76 homologous neurotoxin sequences suggested that the "toxic" domain of these compounds consists of twelve highly conserved residues. Five of these, namely Lys-27, Trp-29, Asp-31, Arg-33 and Glu-38, together with a variant residue at position 36 are organized into a pattern which resembles that of d-tubocurarine. Two lines of experimental evidence are in agreement with the proposed topology of the "toxic" site in Naja nigricollis toxin alpha--Three highly conserved residues (Lys-27, Trp-29 and Lys-47) have been modified individually in toxin alpha. These modifications induce a decrease in binding affinity of toxin alpha for its target, the nicotinic acetylcholine receptor. In contrast, modifications of three residues (Leu-1, Lys-15 and Lys-51) excluded from the "toxic" domain, do not alter the binding properties of toxin alpha.--Five toxin derivatives carrying a nitroxide group at residues 1, 15, 27, 47 or 51 have been prepared. ESR spectra have been recorded for each derivative in both the free state and bound to the receptor. Mobility of the probes of the residues excluded from the "toxic" site is not altered upon receptor binding. In contrast mobility of the nitroxide of the presumed "toxic" Lys-47 becomes markedly reduced after toxin receptor complex formation. Lys-27 nitroxide is immobilized in both the free and bound state. The antigenic structure of N. nigricollis toxin alpha has been partially clarified using two different approaches. --Fifteen antigenically important residues of toxin alpha have been identified by analyzing cross-reactions between toxin alpha and eleven homologous neurotoxins, using polyclonal antibodies.--- One monoclonal antibody (M alpha 1) specific for toxin alpha has been prepared. Competition experiments, made with (3H) toxin alpha, six mono modified toxin derivatives or alpha three homologous neurotoxins, showed that the binding site of (M alpha 1) comprises the N-terminal group, Lys-15, Pro-18 and probably Thr-16. This site is topographically different from the "toxic" domain. (M alpha 1) inhibits the toxicity of toxin alpha under both in vivo and in vitro conditions. In addition, (M alpha 1) is capable of "removing" toxin molecules bound to the receptor, allowing a rapid recovery of the functional properties of the receptor.     

Replacement of lysine by arginine, phenylalanine and tryptophan in the reactive site of the bovine trypsin-kallikrein inhibitor (Kunitz) and change of the inhibitory properties.

The reactive-site sequence of a proteinase inhibitor can be written as . . . -P3-P2-P1-P'1-P'2-P'3- . . . , where-P1-P'1-denotes the reactive site. Three semisynthetic homologues have been synthesized of the bovine trypsin-kallikrein inhibitor (Kunitz) with either arginine, phenylalanine or tryptophan in place of the reactive-site residue P1, lysine-15. These homologues correspond to gene products after mutation of the lysine 15 DNA codon to an arginine, phenylalanine or tryptophan DNA codon. Starting from native (virgin) inhibitor, reactive-site hydrolyzed, still active (modified) inhibitor was prepared by chemical and enzymic reactions. Modified inhibitor was then converted into inactive des-Lys15-inhibitor by reaction with carboxypeptidase B. Inactive des-Lys15-inhibitor was reactivated by enzymic replacement of the P1 residue according to Leary and Laskowski, Jr. The introduction of arginine was catalyzed by an inverse reaction with carboxypeptidase B, while phenylalanine or tryptophan were replaced by carboxypeptidase A. The reactivated semisynthetic inhibitors were trapped by complex formation with either trypsin or chymotrypsin. The enzyme - inhibitor complexes were subjected to kinetic-control dissociation, and the semisynthetic virgin inhibitors were isolated. The inhibitory properties of the semisynthetic inhibitors have been investigated against bovine trypsin and chymotrypsin and against porcine pancreatic kallikrein and plasmin. The homologues with either lysine or arginine in the P1 position are equally good inhibitors of trypsin, plasmin and kallikrein. The Arg-15-homologue is a slightly more effective kallikrein inhibitor than the Lys15-inhibitor. The semisynthetic phenylalanine and tryptophan homologues, however, are weak inhibitors of trypsin and still weaker inhibitors of kallikrein, but are excellent inhibitors of chymotrypsin. Their association constant with chymotrypsin is at least ten times higher than that of native Lys-15-inhibitor. A dramatic specificity change is observed with the phenylalanine and tryptophan homologues, which in contrast to the native inhibitor do not at all inhibit porcine plasmin. Thus, the nature of the P1 residue strongly influences the primary inhibitory specificity of the bovine inhibitor (Kunitz).     

The sites of neurotoxicity in alpha-cobratoxin

We have chemically modified groups of amino acids in the sequence of alpha-cobratoxin and have studied the derivatives as to their affinity of binding to the acetylcholine receptor protein from Torpedo marmorata. (i) The toxin derivatives which were fully modified at lysine (penta-epsilon-N,N-dimethyl lysine; penta-epsilon-N-acetyl lysine), arginine (penta-N7,N8-(1,2-dihydroxycyclohex-1,2-ylene arginine), and tyrosine (mononitrotyrosine) all had significant remaining toxicity and affinity of binding. (ii) The "extra" disulfide of alpha-cobratoxin was selectively reduced and alkylated. Depending on the charge, size, and hydrophobicity of the attached groups, derivatives were obtained that bound to the acetylcholine receptor with higher (di-S-carboxyamidomethyl), about equal (di-S-pyridylethyl), or lower (di-iodoacetaminoethylnaphthylamine-5-sulfonic acid) affinity than the unmodified toxin. (iii) A fully reduced and carbamidomethylated derivative of alpha-cobratoxin obtained by repeating the procedure for selective reduction six times still bound with appreciable affinity (KD approximately 3 X 10(-6) M) to the acetylcholine receptor. We conclude that neither a single positively charged residue nor tyrosine nor the integrity of the disulfides is absolutely essential for toxicity. Furthermore, the single tyrosine and the area around the extra disulfide do not participate in the binding to the receptor. Together with previous findings on this interaction, this suggests a multipoint attachment of toxin and receptor involving several locally separate structural elements of the toxin.     

Conformation, enzymic activity, and immunochemistry of a lysozyme derivative modified at tryptophan 123 by reaction with 2,3-dioxo-5-indolinesulfonic acid.

Reaction of hen egg-white lysozyme with 2,3-dioxo-5-indolinesulfonic acid (DISA) yielded a homogeneous derivative which was modified at a single tryptophan residue. The modification was located at Trp-123. The absorption spectrum of the derivative showed a new peak in the visible range with lambdamax at 365 nm. In addition, the absorption maximum in the ultraviolet which appears in lysozyme at 280 nm was shifted to 270 nm in the derivative and appreciably enhanced. In ORD measurements, the rotatory behaviors of lysozyme and its derivative were identical at the 233 nm negative minimum and the 199 nm positive extremum. CD measurements gave equal [theta] values for lysozyme and derivative at the two negative ellipticity bands at 208 and 220 nm. Although no conformational differences between lysozyme and derivative were observed by ORD and CD measurements, some changes were detectable by chemical methods. Accessibility to tryptic hydrolysis and susceptibility of the disulfide bonds to reduction were increased in the derivative relative to lysozyme. The lytic activity of the derivative, which retained the same pH optimum as native lysozyme, was greatly (50%) decreased, probably as a result of the slight conformational change. With several antisera to lysozyme, the native protein and its derivative had equal antigenic reactivities. The findings were instrumental in further delineation of an antigenic reactive site in lysozyme.