Disulfide-bridged Peptides Research Articles

Antibody responses raised against a conformational V3 loop peptide of HIV-1.

The amino acid sequence of the principal neutralizing determinant (PND) of 224 cases of human immunodeficiency virus type 1 (HIV-1) was determined and the most frequently occurring sequence was used as a peptide antigen for studying virus-specific antibody responses. In our present study, a linear peptide of the most frequent PND was first synthesized and then oxidized to create a disulfide-bridged loop conformation. Then, in order to construct a macromolecular structure for the purpose of increasing antigenicity, the synthetic peptide was conjugated to a core peptide. We compared the immunogenicity of the disulfide-bridged loop PND peptide antigen (AG4) and the linear PND peptide antigen (AG5). After immunizing rabbits 5 and 6 times with both peptides, the results obtained using ELISA revealed that AG4 (conformational-loop type) was more capable of inducing a high titer of antigen-specific antibodies than was AG5 (linear type). Despite an amino acid sequence homology of 72%, a 1:8 dilution of serum raised against AG4 inhibited 81.9% of HIV-1IIIB-mediated cell fusion, suggesting that conformational V3 loop peptide is able to elicit an antibody response which is strongly HIV-1-specific.

Conformational differences between cis and trans proline isomers of a peptide antigen representing the receptor binding domain of Pseudomonas aeruginosa as studied by 1H-NMR.

A 17-residue disulfide-bridged peptide (PAK 128-144) corresponding to the C-terminus of Pseudomonas aeruginosa pilin strain K has been studied by one- and two-dimensional nmr techniques. This synthetic immunogen has been found to exist as two distinct conformations in solution, which have been demonstrated to arise as a result of the isomerization of the I138-P139 amide bond. The two isomers occur in the ratio of 3:1 trans to cis at 5 degrees C. Sequential assignments for both forms have been accomplished through the use of nuclear Overhauser enhancement spectroscopy (NOESY) spectra and most side-chain resonances have been assigned using a combination of correlated spectroscopy, total correlated spectroscopy, and NOESY spectra. The presence of the cis isomer, which is considerably more predominant in the oxidized peptide, was confirmed by the observation of the characteristic NOEs between P139 and the preceding residue. Further corroboration was given by the disappearance of the cis resonances in the spectrum of the P139A analogue of PAK 128-144. From observation of the differences in the chemical shifts and amide proton temperature coefficients of the two isomers, it is apparent that the two forms differ markedly in their solution conformation. The biological implications of the isomerization are discussed.

Interaction of Antistasin-Related Peptides with Factor Xa: Identification of a Core Inhibitory Sequence

Antistasin, isolated from the Mexican leech, is a 119 amino acid protein which is a selective and potent inhibitor of coagulation Factor Xa. Previous studies indicated that an arginine residue located at position 34 of the inhibitor was cleaved by Factor Xa during the inhibition reaction. To evaluate this residue as the reactive site of antistasin, and to define shorter fragments of antistasin displaying Factor Xa-inhibitory activity, a series of peptides were synthesized corresponding to amino acids 27-49 of the inhibitor. The most potent peptide synthesized was a disulfide-bridged, 19 amino acid peptide, ATS29-47, which inhibited Factor Xa with a Ki = 35 nM, and increased plasma clotting times by over 4-fold at a concentration of 33 uM. Reduction or sulfation of the cysteine residues in ATS29-47 reduced Factor Xa inhibitory activity by over 95%. Peptides as short as seven residues corresponding to position 33-39 of antistasin displayed Factor Xa inhibitory activity. The peptides did not inhibit thrombin or trypsin at concentrations 1000-fold higher than used in Factor Xa assays. The shortest peptide displaying anticoagulant activity in human plasma was the disulfide-bridged peptide, D-Arg-Cys-Arg-Val-His-Cys-Pro, which increased clotting times by 50% at micromolar concentrations. These results demonstrate that antistasin-related peptide sequences can serve as model structures for the development of novel, low molecular weight anticoagulants.

NMR solution structure and flexibility of a peptide antigen representing the receptor binding domain of Pseudomonas aeruginosa.

A synthetic peptide antigen corresponding to the C-terminus of Pseudomonas aeruginosa K strain pilin has been studied by one and two-dimensional NMR techniques. This peptide exists in two isomeric forms which arise as a result of the I138-P139 amide bond. An ensemble of solution conformations for the trans form of this 17-residue disulfide-bridged peptide (PAK 128-144) has been generated using a simulated annealing procedure in conjunction with distance and torsion angle restraints derived from NMR data. One major class of backbone conformations has been identified for this potential synthetic vaccine and indicates the presence of two beta-turns in the region 134-142. The region that has been established as the epitope for the monoclonal antibody PK99H is consistent with the region of the major conformers that exhibit the most definition in the ensemble (134-140) and also includes a type I beta-turn from residues 134 to 137. The generated structures are also consistent with observed NOEs characteristic of beta-turns and amide proton temperature coefficient data, which indicate the presence of two turns between residues 134 and 142. The presence of secondary structure within the epitope substantiates the theory that immunogenic regions of proteins are those which contain surface-exposed structural elements such as beta-turns. Further implications of the structure on antigenicity and cross-reactivity are discussed.

Geometry optimization, energetics and solvation studies on four- and five-membered cyclic and disulfide-bridged peptides, using the programs quanta 3.3 and charmm 22

Force field parameters for peptides and proteins in the charmm 22 force field have been refined using the results of MP2/6-311G ∗∗ calculations on N-formyl alanine amide (Frey et al., J. Am. Chem. Soc., 114 (1992) 5369) and other data (Remek et al., J. Mol. Struct. (Theochem), 235 (1991) 1). Significant changes in the peptide backbone torsional energy terms in charmm 22 were made in order to be consistent with the MP2 results relative to previously fitted HF results. To test the new force field parameters against experimental data, molecular mechanics calculations were carried out on small four- and five-membered cyclic and disulfide-bridged peptides. It was found that in general these molecules are in their calculated minimum energy conformation or a low energy conformation in the X-ray structure. The average deviation of the dihedral angles calculated for the seven energy minimized vacuum structures from the X-ray values is 10°. The dihedral angle deviations of the minimized and dynamically averaged conformations are similar for studies which included explicit TIP3P solvent molecules. Upon solvation and minimization, internal vacuum energies increase by 4–7 kcal mol −1. In addition to calculated structural results, we report some of the force field parameters used for the calculations, energy decompositions, and harmonic vibrational free energies.

Peptide models of protein folding initiation sites. 3. The G-H helical hairpin of myoglobin.

As part of an extensive dissection of the folding pathway of myoglobin, a series of peptides corresponding to fragments of sperm whale myoglobin have been synthesized, and their conformational preferences investigated using circular dichroism and nuclear magnetic resonance spectroscopy in aqueous solution and in solvent mixtures containing water and trifluoroethanol. The behavior of short fragments corresponding to the sequences of the G- and H-helices of myoglobin and to the turn region between these helices has been described in accompanying papers. At the next level of complexity, peptide model compounds have been synthesized to explore the longer-range interactions which may take place in protein folding after initial secondary structure formation has occurred. A series of disulfide-bridged dimeric peptides containing the complete sequences of the G- and H-helices of myoglobin were synthesized and their conformational preferences examined. CD spectra indicate that disulfide-bridged peptides consisting of two H-helix sequences (Mb-HssH) and of one G- and one H-helix (Mb-GssH) are highly helical in water solution, as a result of intermolecular association. A 51-residue peptide, Mb-GH51, encompassing the entire G-H helical hairpin of myoglobin, including the turn sequence between the two helices, has been successfully synthesized by standard methods. This peptide was designed to be monomeric in aqueous solution. Mb-GH51 does not appear from CD spectra to contain any additional helix in water solution above what would be expected from an equimolar mixture of the G- and H-helix peptides. NMR spectra indicate that the turn conformation observed in shorter peptide fragments is retained in Mb-GH51 in high population.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the bioactive form and molecular determinants of recognition of cyclic enkephalin peptides at the δ‐opioid receptor

An extensive and systematic search strategy to determine the conformational profile of 12 cyclic disulfide-bridged opioid peptides with varying affinities at the delta receptor has been carried out to identify the structure that is recognized by the delta receptor for each analogue. The methods and procedures used here for the conformational search have already been validated for [D-Pen2,D-Pen5] enkephalin (DPDPE), one member of this family. Use of these methods led to a low-energy solution conformation of DPDPE in excellent agreement with all the geometric properties deduced from its solution nmr spectra. Each of the analogue was subjected to the same procedure, involving a combination of molecular dynamics simulations at high and low temperature. The study was repeated in two environmental conditions, an apolar environment, simulated by using a distance-dependent dielectric constant, and a polar environment by embedding the peptides in a high constant dielectric (epsilon = 80). An automated comparison of the different conformers based on their backbone rms and average distance between the key aromatic moieties was followed by graphic analysis using maximum structural overlap. The cross-comparison of the conformations for each analogue revealed a unique conformer that may be recognized by the delta receptor for each high-affinity analogue that permitted maintaining the critical elements required for recognition in a simple spatial orientation, while maximizing similarity in other regions.

Design of potent and specific integrin antagonists. Peptide antagonists with high specificity for glycoprotein IIb-IIIa.

Members of the snake venon-derived, "disintegrin" peptide family containing the Arg-Gly-Asp (RGD) amino acid sequence are among the most potent inhibitors of the binding of adhesive proteins to platelet glycoprotein (GP) IIb-IIIa. However, GPIIb-IIIa antagonists containing the RGD sequence are not integrin specific and inhibit the adhesive functions of many other RGD-dependent integrins. The single disintegrin peptide, barbourin, containing a conservative amino acid substitution of Lys (K) for Arg (R) in the RGD sequence, is however, highly specific for GPIIb-IIIa. Using this information we have tested the hypothesis that both structural and conformational elements of barbourin are important for its high affinity and selectivity for platelet GPIIb-IIIa by synthesizing a series of conformationally constrained, disulfide-bridged peptides containing the KGD amino acid sequence. Incorporation of the KGD sequence into a cyclic peptide template, followed by systematic optimization of the cyclic ring size, optimization of secondary hydrophobic binding site interactions, and the derivatization of the lysyl side chain functionality of the KGD sequence has resulted in peptide analogs which display inhibitory potency and GPIIb-IIIa selectivity comparable to that of barbourin. This study demonstrates that the specificity and potency of the disintegrin family of antagonists, in particular barbourin, can be mimicked by small, conformationally restrained peptides.

Identification of antigenic residues on apamin recognized by polyclonal antibodies

The structural requirements for antigenic recognition of apamin—an 18-amino acid, disulfide-bridged peptide—by rabbit antibodies were defined using a set of 18 apamin analogs in a competition liquid-phase radioimmunoassay. Some residues contribute considerably to antigenic recognition, e.g. Ala 10, Arg 13, and others to a lesser extent, e.g. Arg 14, Glu 7 and Thr 8. The N- and C-terminal moieties of apamin are less antigenically important. These findings suggest that a good part of antibody specificities are directed to the central tightly folded part of the molecule. They are consistant with the observation that in saturating conditions, labeled apamin can, on average, bind one specific Fab fragment.

Effect of trifluoroacetic acid on the reduction of disulfide bridges in peptides analyzed by fast‐atom bombardment mass spectrometry

Some of the factors that influence the reduction of disulfide-containing peptides under fast-atom bombardment have been investigated using two neurohormonal peptides that include disulfide bridges in their structures. Deaminoarginine-vasopressin (DAVP) and arginine-vasopressin (AVP) have been analyzed as their acetate and trifluoroacetate salts. Results obtained in a thioglycerol matrix indicate that the peptides analyzed as their acetate salts are completely reduced under bombardment, whereas the trifluoroacetate salts show little evidence of reduction. Addition of trifluoroacetic acid to the acetate sample prior to bombardment inhibits reduction whereas addition after bombardment shows no effect on the reduction, thereby indicating the irreversibility of the process. Time-monitoring experiments conducted with the acetate salts of DAVP and AVP in common matrices such as thioglycerol, dithiothreitol + diethioerythritol, glycerol, hydroxyethyldisulfide and nitrobenzyl-alcohol demonstrate an important effect of the chemical nature of the matrix on reduction. In matrices containing thiol groups, the reduction is extensive, whereas it is almost suppressed in matrices such as hydroxyethyldisulfide and nitrobenzylalcohol. However, the addition of trifluoroacetic acid to all of these matrices essentially eliminates reduction and provides measured isotopic peak ratios that are in agreement with theoretically calculated values for these peptides.

Characterization of the major proteins from Vitis vinifera seeds

The major protein from the endosperm of Vitis vinifera cv. Chardonnay is a globulin, homogeneous by size ( M τ ⩾ 400 kD after PAGE) and highly heterogenous by charge, 23 bands being resolved by IEF, with pI values 4.8–5 for the major components, and up to pH 7 for the minor ones. The native structure is assembled from non-covalently bound subunits, with M r which in turn are composed of disulfide-bridged peptides, M τ 19–21 kD and 38–44 kD. The focusing pattern of the denatured protein includes 15 acidic (pI values = 4.25–4.8) and two alkaline ( M τ = 26 kD, pI = 6.8–6.9) components. None of the major bands contains sugar or lipid mojeties. Several enzymatic activities are detected: esterase, phosphoglucomutase, acid phosphatase, peroxydase, malic, alcohol and a little lactic dehydrogenase; no protease inhibitors can be identified. The quali-quantitative variability among proteins extracted from individual seeds amounts to approx. 10%; only large samples, including 20–30 seeds, are thus likely to be representative of the genetic set-up of a given Vitis clone.

The arrangement of intra- and intermolecular disulfide bonds in the carboxyterminal, non-collagenous aggregation and cross-linking domain of basement-membrane type IV collagen.

The hexameric complex of globular domains of type IV collagen was isolated after collagenase digestion of human placenta and the different monomers and dimers present were chromatographically separated. The ratio of alpha 1(IV)NC1 to alpha 2(IV)NC1 was 2:1. About 50% of the NC1 domains were connected to dimers. Predominantly alpha 1-alpha 1 dimers were found. Only 12% were alpha 2-alpha 2 dimers and no alpha 1-alpha 2 dimers could be detected. The majority (88%) of the intermolecular bonds was found to be disulfide bridges. The remainder could not be cleaved by reduction. To elucidate the arrangement of the disulfide bonds, the unreduced alpha 1(IV)NC1 monomers were treated with cyanogen bromide, the disulfide-bridged peptides isolated and characterized by Edman degradation. Each of the two homologous subdomains within a monomer is stabilized by an identical set of three disulfide bonds. In subdomain I, cysteines at positions 20 and 53 are connected with the C-terminal cysteine pair 108 and 111. Thus formed, the disulfide knot stabilizes two interconnected loops of 32 and 54 residues, respectively. A smaller loop of five residues occurs due to a disulfide bond between the cysteines 65 and 71. A similar disulfide arrangement is indicated for subdomain II which is separated from subdomain I by a segment of 20 amino acid residues. The same arrangement of disulfide bonds has been strongly suggested for the alpha 2(IV)NC1 monomer by the isolation and characterization of its disulfide-bridged tryptic fragments. Similar investigations on the dimeric alpha 1(IV)NC1 domain established the arrangement of the intermolecular disulfide bonds. They are formed by a complete disulfide exchange between corresponding disulfide knots of two monomeric NC1 domains.

Antigenic determinants on human choriogonadotropin alpha-subunit. I. Characterization of topographic sites recognized by monoclonal antibodies.

Immunochemical studies were designed to localize antigenic regions recognized by two monoclonal antibodies directed against the alpha-subunit of human choriogonadotropin (hCG-alpha) and to provide information on the three-dimensional structure of hCG and its alpha-subunit. Monoclonal antibody HT13 bound to a region accessible on both hCG and the free alpha-subunit, whereas monoclonal antibody AHT20 recognized a site localized only on the free alpha-subunit. By studying the cross-reactivity of these antibodies to homologous proteins, we found that antibody HT13 did not bind to equine or ovine lutropin, whereas AHT20 was capable of binding to both subunits. This observation suggests that AHT20 recognized a structurally related antigenic determinant on alpha-subunits of different species. To delineate the portions of hCG-alpha contributing to the antigenic determinants of AHT20 and HT13, we performed competitive inhibition assays using reduced and carboxymethylated hCG-alpha, deglycosylated hCG-alpha, hCG-alpha minus the 5 COOH-terminal residues (hCG-alpha core 1), or disulfide-bridged peptides comprising residues 1-35 and 52-91 of hCG-alpha (hCG-alpha core 2). Reduced and carboxymethylated hCG-alpha did not inhibit the binding of 125I-labeled hCG-alpha to both antibodies, whereas deglycosylated hCG-alpha was as active as hCG-alpha, suggesting that antigenic determinants of both antibodies are mainly discontinuous and do not reside on the oligosacharide part of the alpha-subunit. hCG-alpha core 1 had the same capacity as intact hCG-alpha to inhibit the binding of 125I-hCG-alpha to both antibodies, indicating that the 5 COOH-terminal residues of hCG-alpha do not participate in the antigenic determinants. hCG-alpha core 1 was as potent as hCG-alpha in inhibition experiments performed with HT13, whereas, in striking contrast, hCG-alpha core 2 did not compete with 125I-hCG-alpha for binding to AHT20, suggesting that the peptides released after proteolysis of the alpha-subunit by trypsin participate in the epitope of AHT20 and are not included in the antigenic determinant of HT13. In an attempt to elucidate the amino acid residues constituting the antigenic sites of HT13 and AHT20, hapten inhibition experiments were carried out using as competitive inhibitors five different synthetic peptides spanning the primary structure of hCG-alpha. None of these peptides inhibited the binding of 125I-hCG-alpha to HT13. In contrast, two peptides analogous to regions 23-43 and 33-59 of hCG-alpha exhibited significant potency in competing with 125I-hCG-alpha for binding to AHT20.(ABSTRACT TRUNCATED AT 400 WORDS)

Structure of the Human Chorionic Gonadotropin β-Subunit Fragment from Pregnancy Urine*

A major portion of the hCG immunoreactivity detectable in pregnancy urine is derived from a fragment of hCG beta. This lacks the COOH-terminal portion of hCG beta, but retains immunoreactivity with most antibodies raised against the beta-subunit of hCG. To improve clinical measurements of hCG and assess the importance of such fragments in human urine, we have isolated and determined the structure of this molecule. The hCG beta fragment was isolated from a partially purified commercial preparation of hCG (Organon) by gel filtration and immunoaffinity chromatography using monoclonal antibodies. It was found to consist of two polypeptide chains composed of residues beta-(6-40) disulfide-bridged to residues beta-(55-92). It also differs from the beta-subunit of hCG in its carbohydrate structure, lacking sialic acid and having a low but variable amount of galactose. A beta-fragment containing the same two NH2-terminal sequences was also isolated from a single pregnant woman's urine. The two major polypeptides comprising the beta-fragment contain a total of nine half-cystine residues, raising the possibility that a free thiol may exist or that a third undetected disulfide-bridged peptide is present in the intact fragment. However, tests for the presence of a free thiol have been negative. Another intrinsic characteristic of the beta-fragment is the formation of a variable amount of dimer in solutions of neutral pH. beta-fragment will not combine with intact alpha-subunit. Despite the absence of regions beta-(1-5), beta-(41-54), and beta-(93-145), the beta fragment is recognized by the SB-6 antibody and most monoclonal antibodies elicited to the beta-subunit, thus excluding half of the amino acids of the beta-subunit from the epitope(s) where these antibodies bind.

Tryptic digestion of the alpha subunit of human choriogonadotropin.

In order to further characterize chemical, physicochemical, and immunochemical properties, as well as structure-function relationships, of the common alpha subunit of human glycoprotein hormones, a tryptic core was prepared from the alpha subunit of human choriogonadotropin. The core was purified in greater than 80% yield using gel permeation and anion-exchange chromatography, and, following reduction and S-carboxymethylation, the constituent peptides were purified by gel permeation and high performance liquid chromatography. The disulfide-bridged peptides comprising the alpha core were identified as residues 1-35 and residues 52-91 by amino acid composition and amino acid carboxyl sequence analyses of the reduced, S-carboxymethylated peptides. The alpha tryptic core contained both N-asparagine carbohydrate moieties, but was devoid of residues 36-51 and the carboxyl-terminal serine at position 92. The small peptides cleaved from residues 36-51, a known potential O-glycosylation region of the alpha subunit, were purified and identified. The tryptic core retained full immunopotency relative to the intact subunit in the binding to polyclonal and monoclonal antibodies directed against the alpha subunit. The region consisting of residues 36-51 is not part of the epitope recognized by these antibodies. With antisera generated to the reduced, S-carboxymethylated subunit, peptide 1-35, but not 52-91, was immunoreactive. This finding is consistent with the known dominant antigenicity of the amino-terminal region in the reduced, S-carboxymethylated molecule. The core exhibited no appreciable interaction with the complementary beta subunit, and, not surprisingly, was unable to compete with intact hormone binding in a radioreceptor assay using rat testicular homogenates. Circular dichroic spectroscopy was used to probe gross features of tertiary structure (240-300 nm) and secondary structure (190-240 nm). The tryptic core and each of the two constituent peptides exhibited spectra above 240 nm that resembled that of the reduced, S-carboxymethylated subunit more than that of the native material, thus suggesting a significant loss of tertiary structure in the core and isolated peptides. This finding is unexpected in consideration of the full retention of immunopotency by the alpha core although consistent with failure of the core to combine with intact complementary beta subunit. The intact subunit as well as the isolated constituent peptides exhibit little if any helicity in aqueous solution. Interestingly, the reduced, S-carboxymethylated chain and peptide 52-91 displayed helicity in 80% trifluoroethanol, a helicogenic solvent.

ChemInform Abstract: CYCLIC PEPTIDE DISULFIDES. SOLUTION AND SOLID‐STATE CONFORMATION OF BOC‐CYS‐PRO‐AIB‐CYS‐NHME WITH A DISULFIDE BRIDGE FROM CYS TO CYS, A DISULFIDE‐BRIDGED PEPTIDE HELIX

Chemischer InformationsdienstVolume 14, Issue 16 Physical Organic Chemistry ChemInform Abstract: CYCLIC PEPTIDE DISULFIDES. SOLUTION AND SOLID-STATE CONFORMATION OF BOC-CYS-PRO-AIB-CYS-NHME WITH A DISULFIDE BRIDGE FROM CYS TO CYS, A DISULFIDE-BRIDGED PEPTIDE HELIX A. RAVI, A. RAVISearch for more papers by this authorB. V. V. PRASAD, B. V. V. PRASADSearch for more papers by this authorP. BALARAM, P. BALARAMSearch for more papers by this author A. RAVI, A. RAVISearch for more papers by this authorB. V. V. PRASAD, B. V. V. PRASADSearch for more papers by this authorP. BALARAM, P. BALARAMSearch for more papers by this author First published: April 19, 1983 https://doi.org/10.1002/chin.198316056AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, Issue16April 19, 1983 RelatedInformation

Cyclic peptide disulfides. Solution and solid-state conformation of Boc-Cys-Pro-Aib-Cys-NHMe with a disulfide bridge from Cys to Cys, a disulfide-bridged peptide helix

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCyclic peptide disulfides. Solution and solid-state conformation of Boc-Cys-Pro-Aib-Cys-NHMe with a disulfide bridge from Cys to Cys, a disulfide-bridged peptide helixA. Ravi, B. V. Venkataram Prasad, and P. BalaramCite this: J. Am. Chem. Soc. 1983, 105, 1, 105–109Publication Date (Print):January 1, 1983Publication History Published online1 May 2002Published inissue 1 January 1983https://doi.org/10.1021/ja00339a019RIGHTS & PERMISSIONSArticle Views394Altmetric-Citations74LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (598 KB) Get e-Alerts Get e-Alerts

Peptide and protein labelling with iodine, iodine monochloride reaction with aqueous solution of L‐tyrosine, L‐histidine, L‐histidine‐peptides, and his effect on some simple disulfide bridges

AbstractIodinated peptides or proteins (125I, 131I) are used as tracers for radioimmono assays and for detection in biological systems. The labelling takes place on the aromatic side chains.However, when disulfide bridges are present, iodination must be carried out under conditions preventing their degradation. The rate of iodination of L‐tyrosine, L‐histidine and L‐histidine containing peptides by iodine monochloride (ICI) are studied by spectroscopy. Free hitidine increases the hydrolysis rate of aqueous solution of ICI. The interactions between ICI and some simple disulfide are investigated by circular dichroism measurements. These reactions are presented as models for degradation of disulfide bridges in peptide or protein during the iodination process.