bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation of partially protected des‐alanineB30 ‐insulin‐B‐chain‐disulphide and its use in semisynthesis*
Authors: Büllesbach Erika E. , Schmitt Ernst W. , Gattner Hans‐Gregor
Published: August 2010

The preparation of Nα1N29‐bis‐methylsulphonylethyloxycarbonyl‐des‐alanineB30‐B‐chain‐disulphide‐OΛ13OΛ21‐dimethyl ester is described. Starting with the di‐S‐sulphonate‐B‐chain it was prepared by i) removal of the C‐terminal amino acid by digestion with carboxypeptidase A, ii) reduction and oxidation to form the cyclic disulphide, iii) esterification of the three carboxyl groups (αCOOH = LysB29, ΛCOOH = GluB13 and GluB21) followed by selective tryptic hydrolysis of the α‐carboxyl ester, and iv) the protection of both amino groups (αNH2= PheB1, NH2= LysB29). This B‐chain derivative was activated selectively at the C‐terminal carboxyl group by formation of a mixed anhydride, and condensed with the dipeptide Thr‐Arg. All protecting groups were removed by treatment with alkali. The human‐B‐chain C‐terminal elongated with Arg was obtained in a yield of 30% based on the protected des‐AlaB30‐B‐chain derivative.
Cyclic peptides
Authors: Yasutake Akira , Aoyagi Haruhiko , Sada Isao , Kato Tetsuo , Izumiya Nobuo
Published: August 2010

Cyl‐2 is a phytotoxic cyclic tetrapeptide with the sequence of cyclo(‐D‐Tyr(Me)‐L‐Ile‐L‐Pip‐Aoe‐): Aoe, 2‐amino‐8‐oxo‐9,10‐epoxydecanoic acid. The configuration of Aoe is unknown. Three analogs, cyclo(‐D‐Tyr(Me)‐L‐Ile‐L‐Pip‐L(and D)‐Leu‐) (1 and 2) and cyclo (‐D‐Tyr(Me)‐L‐Ile‐L‐Pro‐D‐Leu‐) (3), were synthesized and spectroscopic features of these analogs were compared. 1 H‐N.m.r. spectra of cyclo(‐D‐Tyr(Me)‐L‐Ile‐L‐Pip‐L‐Leu‐) (1), cyclo(‐D‐Tyr(Me)‐L‐Ile‐L‐Pro‐L‐Leu‐) (4), and Cyl‐2 showed a similar pattern. On the other hand, the spectra of analogs 2 and 3 showed a different pattern, the Ile‐Pro bond in 3 being in cis conformation.
Galactofuranosyl‐containing glycopeptide of Penicillium charlesii: Vacuum ultraviolet circular dichroism
Authors: HERSCHLAG DANIEL , STEVENS E.S. , GANDER J.E.
Published: August 2010

The far and vacuum u.v. circular dichroism (CD) of peptidophosphogalactomannan from P. charlesii is reported to 182.5 nm in aqueous and aqueous/organic solvents, and to 150 nm in films. CD of films of the peptide‐free derivative is reported to 150 nm. On the basis of these data we conclude that the peptide chain is unordered, and may best be described as a hydrated coil showing some stiffness. The small observed saccharide CD may result from cancellation of contributions from the various saccharide structures present or from a lack of repeating secondary structure.
Synthesis of 2‐methyl and 2‐carboxymethyl derivatives of ornithine and arginine
Authors: UNSON CECILIA G. , ERICKSON BRUCE W.
Published: August 2010

Synthesis and characterization of a dozen derivatives of ornithine and arginine bearing 2‐methyl or 2‐carboxymethyl substituents are described. These substituents were introduced by dilithiation of 3‐(4‐methoxybenzylidineamino)‐2‐piperidinone with lithium diisopropylamide followed by regiospecific alkylation at C‐3 with iodomethane or ethyl bromoacetate. 2‐Methyl‐d,l‐ornithine was obtained in three steps from 3‐amino‐2‐piperidinone in 68% overall yield, and 2‐carboxymethyl‐d,l‐ornithine was isolated in 56% overall yield. 2‐Methyl‐and 2‐carboxymethyl‐d,l‐arginine were obtained by mild acid hydrolysis to remove the 4‐methoxybenzylidine group, N ‐acylation with 4‐toluenesulfonyl chloride, mild alkaline hydrolysis of the lactam ring and the ester group, guanidination of the 5‐amino group with O ‐methylisourea, and strong acid hydrolysis to remove the 4‐tolunenesulfonyl group. Several of these compounds are inhibitors of carboxypeptidase B.
Conformational study of the neurotensin and Substance P fragments: Pro‐Arg‐Arg‐Pro and Arg‐Pro‐Lys‐Pro
Authors: COTRAIT MICHEL
Published: August 2010

The conformational behaviour of the basic hydrophilic Pro‐Arg‐Arg‐Pro and Arg‐Pro‐Lys‐Pro peptides, neurotensin (NT) and Substance P fragments, has been taken up by semi‐empirical calculations. The presence of two Pro residues prevents these peptides from giving any folded structure (α helix, β turn.). In both peptides the most stable conformations are essentially relative to more or less stretched structures; structures involving one or more residues in a γ turn form are often encountered in Pro‐Arg‐Arg‐Pro peptide while mixed structures involving residues in very different conformations are found for the Arg‐Pro‐Lys‐Pro‐peptide. In both peptides, positively charged Lys and Arg side‐chains most often point in opposite directions. The Pro‐Arg‐Arg‐Pro peptide is part of the active NT (7–13) fragment where both Arg residues are necessary to the activity. A tentative study shows that the hydrophilic tetrapeptide induces NT (7–13) stretched conformations.
Comparative efficacy of various routes of administration of thymopentin (TP‐5) with consideration of degradative mechanisms
Authors: AUDHYA TAPAN , GOLDSTEIN GIDEON
Published: August 2010

Thymopoietin32–36 (originally termed TP‐5 and now called thymopentin) is a synthetic pentapeptide that can reproduce the biological activity of the 49 amino acid thymic hormone thymopoietin. The efficacy of various routes of administration of thymopentin was studied in mice and guinea pigs using an electromyographic assay as an end point to determine biological activity. In mice, the threshold dose necessary for a significant response when compared to controls was 0.03 mg/kg (mpk) for i.v. (intravenous) injection and 0.3 mpk for both i.p. (intraperitoneal) and s.c. (subcutaneous) injection. For the guinea pig, 0.03 mpk produced a significant response when compared to controls when injected either i.v. or s.c; 0.3 mpk was required for a significant response for i.n. (intranasal) administration and 0.6 mpk for i.p. injection. When saline or plasma was injected, it produced no change in the electromyographic response. In plasma the pentapeptide is rapidly degraded by proteolytic enzymes. Treatment of plasma with specific enzyme inhibitors followed by incubation with thymopentin or thymopoietin confirmed that serine protease and aminopeptidase M‐like enzymes are responsible for the rapid inactivation of thymopentin in plasma, as measured by the electromyographic response.
Synthesis and biological investigations of new tuftsin analogs with elongated peptide chain
Authors: KONOPINSKA DANUTA , LUCZAK MIROSLAW , GUMULKA STANISLAW
Published: August 2010

In this paper the synthesis of the following elongated tuftsin analogs: Thr‐Lys‐Pro‐Lys‐Thr‐Lys‐Pro‐Lys (I), Thr‐Lys‐Pro‐Lys‐Thr‐Lys‐Pro‐Arg (II) and Ala‐Lys‐Thr‐Lys‐Pro‐Arg‐Glu‐Gln (III) by the classical method is described. The compound II markedly inhibited the growth of murine sarcoma viruses (MSV).
Selective ligands for opioid receptors: β‐Cyclopropylalanyl containing analogs of enkephalin
Authors: MUTHUKUMARASWAMY NATESA , DAY ALAN R. , PINON DELIA , LIAO CHUNG SHIN , FREER RICHARD J.
Published: August 2010

The synthesis and resolution of the amino acid β‐cyclopropylalanine (Cpr) and its incorporation into four enkephalin analogs is reported. The analogs prepared were: Tyr ‐l‐ Cpr ‐ Gly ‐ Phe ‐ Pen (des ‐ COOH ‐ Nle =n‐ pentylamide = Pen) (l‐Cpr2‐Pen5‐ENK), Tyr‐d‐Cpr‐Gly‐Phe‐Pen (d‐Cpr2‐Pen5‐ENK),l‐Cpr‐Tyr‐d‐Ala‐Gly‐Phe‐Pen (l‐Cpr0‐d‐Ala2‐Pen5‐ENK) andd‐Cpr‐Tyr‐d‐Ala‐Gly‐Phe‐Pen (d‐Cpr0‐d‐Ala2‐Pen5‐ENK). Each was tested for its ability to inhibit the field stimulated guinea pig ileum (GPI) and rat vas deferens (RVD) and the results compared to the effectd‐Ala2‐d‐Leu5‐enkephalin (DADLE) has on the same preparations. The results show that at concentrations up to 10‐5mall four analogs, as well as DADLE, are full agonists on the GPI preparation. The concentrations necessary to produce a 50% inhibition of the twitch response were, DADLE, 3.5 °× 10‐8m;l‐ Cpr0‐d‐Ala2‐Pen5‐ENK, 6.0 × 10‐8m;d‐Cpr2‐Pen5‐ENK, 1.1 × 10‐7m;l‐Cpr2‐Pen5‐ENK, 1.2 × 10‐6mandd‐Cpr0‐d‐Ala2‐Pen5‐ENK, > 10‐5m. On RVD a different result was observed with only DADLE (1.3 × 10‐6m) andl‐Cpr0‐Pen5‐enkephalin (1.8 × 10‐6m) showing full agonist activity.d‐Cpr2‐Pen5‐ENK was a partial agonist (29 · 5% inhibition of the twitch at 10‐5m) whiled‐Cpr0‐d‐Ala2‐Pen5‐ENK andl‐Cpr2‐Pen5‐ENK did not inhibit the twitch at concentrations up to 10‐5m. These compounds which were inactive or of low potency on each preparation were also tested as antagonists. Onlyd‐Cpr2‐Pen5‐ENK was an antagonist (pA2= 6.09) versus DADLE on RVD whiled‐Cpr0‐d‐Ala2‐Pen5‐ENK was inactive as an antagonist on both GPI and RVD.d‐Cpr2‐Pen5‐ENK, therefore, represents the first enkephalin analog to be categorized as a mixed agonist‐antagonist.
Differentiation of the structural features of melanotropins important for biological potency and prolonged activity in vitro
Authors: WILKES BRIAN C. , SAWYER TOMI K. , HRUBY VICTOR J. , HADLEY MAC E.
Published: August 2010

Several α‐melanotropin (α‐MSH) analogues have been synthesized and tested for their melanotropin activities in order to determine the functional importance of certain amino acids near the primary active sequence of α‐MSH, H‐(Glu)‐His‐Phe‐Arg‐Trp‐Gly‐OH, on the biological activities of the hormone. In particular, we have examined the importance of the 4 and 11 positions in conjunction with the substitution of l‐Phe in position 7 by d‐Phe on potency and prolonged activity of the hormone. In the frog (Rana pipiens) skin system the relative potencies were found to be: [Nle4, d‐Phe7]‐α‐MSH (60) > α‐MSH (1.0) > Ac‐[Nle4, d‐Phe7]‐α‐MSH4–11‐NH2 (0.16) > Ac‐[Nle4, d‐Phe7]‐α‐MSH4–10‐NH2 (0.02) · Ac‐[d‐Phe7]‐α‐MSH5–11‐NH2 (0.01) > Ac‐[Nle4]‐α‐MSH4–10‐NH2 (0.002) = Ac‐[Nle4]‐α‐MSH4–11‐NH2 > Ac‐α‐MSH4–10‐NH2 (0.0003) · Ac‐α‐MSH5–11‐NH2 (0.0002). On the other hand the relative potencies on the lizard (Anolis carolinensis) skin system were found to be: Ac‐[Nle4, d‐Phe7]‐α‐MSH4–10‐NH2 (10) · Ac‐[Nle4, d‐Phe7]‐α‐MSH4–11‐NH2 (8.0) · Ac‐[Nle4, d‐Phe7]‐α‐MSH (5.0) > α‐MSH (1.0) = Ac‐[Nle4]‐α‐MSH4–11‐NH2 = Ac‐[d‐Phe7]‐α‐MSH5–11‐NH2 > Ac‐[Nle4]‐α‐MSH4–10‐NH2 (0.06) > Ac‐α‐MSH5–11‐NH2 (0.01) > Ac‐α‐MSH4–10‐NH2 (0.004). Detailed analyses of these data suggest species‐dependent differences in the stereostructural relationships of the residues in the 4, 7, and 11 positions for melanotropic potency in vitro. Particularly noteworthy is the observation that the 4–11 fragment analogue Ac‐[Nle4]‐α‐MSH4–11‐NH2 is equipotent to α‐MSH in the lizard assay system, suggesting that the 1–3, 12, and 13 residues of α‐MSH are not involved in the binding or transduction in this system.

Examination of the ability of these α‐melanotropin analogues to effect sustained biological activity (prolongation) following removal of exogenous peptide from the bioassay medium showed striking differences in the two systems. On the lizard skin assay, only [Nle4, d‐Phe7]‐α‐MSH, Ac‐[Nle4, d‐Phe7]‐α‐MSH4–11‐NH2 and Ac‐[Nle4, d‐Phe7]‐α‐MSH4–10‐NH2 effect marked prolonged melanotropic activity as compared to α‐MSH. In contrast, on the frog skin assay, only [Nle4, d‐Phe7]‐α‐MSH, Ac‐[Nle4, d‐Phe7]‐α‐MSH4–11‐NH2, Ac‐α‐MSH5–11‐NH2, and Ac‐[Nle4]‐α‐MSH4–10‐NH2 exhibited significant prolonged activity. These results demonstrate that relative potency and prolongation of melanotropic activity are not directly related, but rather are the manifestation of different, species‐dependent structural and topographical requirements for peptide‐receptor interactions related to binding and signal transduction.
Synthesis and characterization of (1 ‐ 13C) Phe9 gramicidin A. Effects of side chain variations
Authors: PRASAD K.U. , TRAPANE T.L. , BUSATH D. , SZABO G. , URRY D.W.
Published: August 2010

The synthesis of (1‐13C)‐Phe9‐gramicidin (90% enriched) was carried out by the solid phase method. The peptide was removed from the resin by treatment with ethanolamine, deblocked, formylated and purified by preparative t.l.c. to obtain the gramicidin analog in an overall yield of 24%. The peptide was verified and characterized by high pressure liquid chromatography, carbon‐13 nuclear magnetic resonance, circular dichroism and single channel currents. Single channel conductances were found to be similar to those of (1‐13C)‐Phe11‐GB but significantly lower than that of gramicidin A. When this gramicidin analog was incubated with phospholipid, the characteristic channel spectrum was not obtained and interaction with sodium ion was not observed. A possible explanation for this behavior is discussed.
Geometrical parameters and shape anisotropy in globular proteins
Authors: PRABHAKARAN M.
Published: August 2010

The anisotropy in the shape of globular proteins is derived by a comparative analysis of three types of geometrical parameters. The role of secondary structures in the design of the shape of globular proteins is worked out.
Synthesis of a cyclic fibrin‐like peptide and its analysis by fast atom bombardment mass spectrometry
Authors: YOUNG JANIS DILLAHA , COSTELLO CATHERINE E. , van LANGENHOVE AGNES , HABER EDGAR , MATSUEDA GARY R.
Published: August 2010

For immunochemical purposes, a cyclic 12‐peptide was synthesized to model the γ‐γ‐chain cross‐link site in human fibrin. The model was based upon the structure proposed by Chen & Doolittle (Biochemistry (1971) 10, 4486–4491) which is characterized by two reciprocating e ‐(γ‐Glu)Lys bonds between adjacent fibrin γ‐chains oriented in an antiparallel manner. To achieve the antiparallel orientation of the peptide backbone, Pro and Gly were inserted at positions 6 and 7 of the linear 12‐peptide: acetyl‐Gly‐Glu‐Gln‐His‐His‐Pro‐Gly‐Gly‐Gly‐Ala‐Lys‐Gly‐amide. The insertions were made to facilitate a reverse turn of the peptide during the last synthetic step, which was formation of the e ‐(γ‐Glu)Lys bond between Glu at position 2 and Lys at position 11 with diphenylphosphorylazide. The resulting cyclic peptide represented half of the symmetrical cross‐linked region in clotted fibrin. Following purification by HPLC, both linear and cyclic 12‐peptides were analyzed by fast atom bombardment mass spectrometry. Abundant molecular protonated ions were observed for both peptides. In addition, the amino acid sequence of the linear peptide and the location of the e ‐(γ‐Glu)Lys bond in the cyclized peptide could be verified.
Approaches to the synthesis of retro‐inverso peptides
Authors: PALLAI P.V. , RICHMAN S. , STRUTHERS R.S. , GOODMAN M.
Published: August 2010

Partial retro‐inverso modification of biologically active peptides is described as a topochemical alteration of the backbone to prevent enzymatic degradation. The preparation ofgem‐diaminoalkyl residues from peptide amides using the reagent [bis(trifluoroacetoxy)iodo] benzene (TIB) is discussed. Treatment ofN‐t‐butyloxycarbonyl tyrosine andN‐t‐butyloxycarbonyl tryptophan with this reagent led to decomposition of the protected amino acids. Protecting the tyrosine and tryptophan residues by t‐butyl ether andNin‐formyl groups, respectively, prevented decomposition and led to good yields of the desired products. Racemic 2‐alkylmalonyl diastereomers were found to be separable by HPLC. The chiral stability of peptides containing optically active malonyl residues was investigated under simulated physiological conditions. Synthetic considerations for the incorporation ofgem‐diaminoalkyl and 2‐alkylmalonyl residues into larger peptides to yield partially modified retro‐inverso peptide analogs are presented.
Synthesis of the C‐terminal half of thymosin α1 by the polymeric reagent method
Authors: MOKOTOFF MICHAEL , PATCHORNIK ABRAHAM
Published: August 2010

In this report we further show the utility and efficiency of polymer‐bound 1‐hydroxybenzotriazole (PHBT) as an almost ideal support for the polymeric reagent method of peptide synthesis. This was demonstrated by the synthesis of thymosin α1 (15–28), in which two suitably blocked segments, Boc‐Asp (OtBu)‐Leu‐Lys (2Cz)‐Glu (OBzl)‐Lys (2Cz)‐Lys (2Cz)‐OH (3) and Boc‐Glu (OBzl)‐Val‐Val‐Glu (OBzl)‐Glu (OBzl)‐Ala‐Glu (OBzl)‐Asn‐OBzl (2), were prepared entirely by utilizing PHBT activation for each coupling step. After appropriate deblocking of 2, segments 2 and 3 were coupled by the DCC‐HOBT method, followed by complete deblocking and ion‐exchange chromatographic purification, affording the C‐terminal half of thymosin α1, H‐Asp‐Leu‐Lys‐Glu‐Lys‐Lys‐Glu‐Val‐Val‐Glu‐Glu‐Ala‐Glu‐Asn‐OH (1).
Structural conservation in globular proteins
Authors: VISWANADHAN V.N. , SUNDARAM K.
Published: August 2010

Some well sequenced classes of homologous proteins have been analysed in the light of their representative tertiary structures to reveal the nature of structural conservation during protein evolution. Within ‘the sphere of influence’ around conserved residue sites preferential association of other conservative sites has been observed to be a feature of natural selection valid for all residue types. An information theory approach evolved to examine residue variability reveals that even some non‐conservative sites scaffold clusters of high biochemical specificity and intermediate folding units.
Assignments of the 270 MHz PMR spectrum of somatostatin using pH titration, synthetic analogs and double resonance difference spectroscopy
Authors: BUFFINGTON LYNN A. , GARSKY VICTOR , RIVIER JEAN , GIBBONS WILLIAM A.
Published: August 2010

We report the assignment procedure for the 270 MHz PMR spectrum in D2O of the 14 amino acid peptide hormone somatostatin,

Ala1 Gly2 Cys3 Lys4 Asn5 Phe6 Phe7 Trp8 Lys9 Thr10 Phe11 Thr12 Ser13 Cys14

using a series of synthetic analogs in which a single amino acid residue was replaced by an Ala residue. The principal methods used were pH titration and extensive double resonance experiments (difference scalar decouplings and nuclear Overhauser effect measurements).
Solid‐phase synthesis and some biological properties of ovine corticotropin‐releasing factor
Authors: LEFÈVRE GÉRARD , VEILLEUX RAYMONDE , LAVOIE MICHEL
Published: August 2010

Ovine corticotropin‐releasing factor (CRF) was synthesized by solid‐phase method and isolated using two purification steps: gel filtration and high performance liquid chromatography. The synthetic peptide is a potent stimulator of ACTH release, as well as cyclic AMP accumulation and release in rat adenohypophyseal cells in culture and shows highly specific binding to bovine anterior pituitary plasma membranes.
Conformational characteristics of homo‐oligopeptides of O‐benzyl‐L‐tyrosine+
Authors: BONORA G.M. , MORETTO V. , TONIOLO C. , ANZINGER H. , MUTTER M.
Published: August 2010

Conformational studies of X [‐L‐Tyr(Bzl)‐]n‐series bound to polyethyleneglycol (X = H2 Nps; n = 3–8) in the solid state and in solvents of different polarities and capabilities of forming hydrogen bonds are reported. By using i.r. absorption, the occurrence of the β‐structure in the higher oligomers in the solid state was established. By means of i.r. absorption and CD the onset of that ordered conformation in solution was assessed as a function of chain length. The effects induced by the presence of the N‐protecting group and added base, and by changing the nature of solvent on the conformational preferences of the [‐L‐Tyr(Bzl)‐]n homo‐peptides were also examined. The 2‐nitrophenylsulphenyl chromophoric derivative of the α‐amino group is proposed as a circular dichroism sensor for β‐structure in peptides.
Residue contacts in protein structures and implications for protein folding
Authors: NARAYANA S.V.L. , ARGOS PATRICK
Published: August 2010

The preferential association of amino acid side groups with specific side chain atoms are examined in 44 known protein structures. The resulting association potentials among residue side groups are used to detect structural homology in proteins displaying little or no homology in their primary sequences. Suggestions are also made regarding the nature of the protein folding process. They are based on statistical observations that delineate the extent of short and long range interactions and that display side group bias in association with other side chain atoms on their N‐terminal side.
Hydrophobic, aza‐glycine analogues of luteinizing hormone‐releasing hormone
Authors: HO TERESA L. , NESTOR JOHN J. , McCRAE GEORGIA I. , VICKERY BRIAN H.
Published: August 2010

The effect of combination of the hydrophilic aza‐Gly substitution (NHNHCO) at position 10 with hydrophobic, unnatural D‐amino acids in position 6 on the potency of luteinizing hormone‐releasing hormone (LH‐RH) analogues has been investigated. Previously the aza‐Gly residue was shown to provide protection from enzymatic cleavage and lead to potency increases in a less hydrophobic series. The compounds were prepared by coupling of the corresponding nona‐peptide acids with semicarbazide hydrochloride by the N,N′‐dicyclohexylcarbodiimide/1‐hydroxybenzotriazole procedure. The required nonapeptide acids were prepared by the solid phase method on chloromethyl‐polystyrene resin using HF/anisole deprotection. The products were purified by preparative reversed‐phase high‐performance liquid chromatography. The analogues were tested in a rat estrous cyclicity suppression assay designed to show the paradoxical antifertility effects of these compounds. The potencies of [6‐(3‐(benz‐imidazol‐2‐yl)‐D‐alanine), 10‐aza‐glycine] LH‐RH and [6‐(3‐(5,6‐dimethylbenzimidazol‐2‐yl)‐D‐alanine), 10‐aza‐glycine] LH‐RH are 40 and 190 times that of LH‐RH respectively. The most active compound in this series is [6‐(3‐(2‐naphthyl)‐D‐alanine), 10‐aza‐glycine] LH‐RH with a potency 230 times that of LH‐RH. This compound is 2.3 times as potent as the standard ([D‐Trp6, Pro9‐NHEt] LH‐RH) and appears to be the most potent LH‐RH agonist reported.
Rapid purification of radioiodinated peptides with Sep‐Pak® reversed phase cartridges and HPLC
Authors: MILLER JAMES J. , SCHULTZ GREGORY S. , LEVY ROBERT S.
Published: August 2010

A simple, rapid method is described for the purification of radioiodinated peptides for use in radioimmuno‐ and in radioreceptor assays. Iodinated reaction mixtures are applied directly onto Sep‐Pak® disposable, reversed phase cartridges equilibrated with phosphate buffer. Unreacted 125‐iodide and other non‐peptide reaction components are eluted with buffer. The peptide fraction is then eluted with 70% buffer:30% acetonitrile. The peptide fraction is further purified by reversed phase high pressure liquid chromatography to separate the native peptide and the mono‐ and diiodo‐derivatives. In this study the method is used to prepare 125‐iodide‐labeled monoiodo‐leucine enkephalin and monoiodo‐angiotensin II, which are free of the parent peptides and diiodo‐derivatives and are of maximum obtainable specific radioactivity. The usefulness of these labeled peptides in radioimmuno‐ and radioreceptor assays is demonstrated by their binding to specific antibodies and receptors, respectively.
Conformation of sequential peptides containing proline residues
Authors: NARITA MITSUAKI , OHKAWA NORIHIRO , NAGASAWA SATOSHI , ISOKAWA SHIZUKO
Published: August 2010

The conformational properties of Boc‐Leu3‐(Pro2GlyLeu3)n‐Pro2Gly‐OH(n = 0, 1, 3, and 5) and Boc‐Leu3‐(Pro2GlyLeu3)n‐Pro2Gly‐OBzl (n = 7, 9, and 11) were investigated in various organic solvents of high polarity using molar rotation and CD measurements. The peptides examined are assembled by the N‐terminal, internal, and C‐terminal segments having the sequences of Boc‐Leu3, Pro2Gly‐Leu3, and Pro2Gly‐OX (X = H or Bzl), respectively. The conformational studies using the molar rotation of the oligopeptides and polypeptides in MeOH, DMSO, DMF, DMA, and NMP have made it clear that all the peptides have a randomly coiled structure. CD spectral patterns of the peptides in MeOH were essentially the same as each other and indicative of the randomly coiled structure. The additive nature of the total molar rotation and total molar ellipticity in Boc‐Leu3‐(Pro2GlyLeu3)n‐Pro2Gly‐OX (X = H or Bzl) indicates that the “peptide segment separation” is indeed in operation in organic solvents of high polarity and that the peptide molecule can be considered to be assembled with the small peptide segments having a randomly coiled structure.
Acyclic peptides as conformational models
Authors: PRASAD B.V. VENKATARAM , BALARAM H. , BALARAM P.
Published: August 2010

The tripeptide Boc‐Aib‐Leu‐Pro‐NHMe crystallizes in the orthorhombic space group P212121 with a = 9.542, b = 15.200, c = 18.256 Å and Z = 4. Each peptide is associated wth two water molecules in the asymmetric unit of the crystal. The structure has been solved by direct methods and refined to an R‐value of 0.069. The peptide adopts a structure without any intramolecular hydrogen bond. The three residues occupy distinctly different regions of the Ramachandran map: Aib in the left‐handed 310‐helical region (± = 67°, ± = 23°), Leu in the β‐sheet region (± = ‐ 133°, ± = 142°) and Pro in the poly (Pro) II region (± = ‐ 69°, ± = 151°). An interesting observation is that each water molecule participates in four hydrogen bonds with distorted tetrahedral coordination about the oxygen atom.
Syntheses of tetra‐ and pentapeptides from skin extracts of Phyllomedusa rhodei (tryptophyllins)*
Authors: PERSEO GIUSEPPE , DE CASTIGLIONE ROBERTO
Published: August 2010

Syntheses by solution methods of tryptophyllins ‐4 and ‐5 (TPH‐4 and TPH‐5), tetra‐ and pentapeptides isolated from the skin extracts of the South American frog Phyllomedusa rhodei, are reported. The incorporation of the Pro2‐Pro3 sequence into pentapeptides and the use of flash chromatography for purification of intermediates and target compounds are discussed. Preliminary biological results seem to indicate a growth‐promoting activity for this peptide family.
Reproducibility of gel‐chromatography
Authors: TESSER GODEFRIDUS I. , ADAMS PETRUS J.H.M. , TEN KORTENAAR PAULUS B.W. , BOOTS HANS A.
Published: August 2010

We think it worthwhile to other experimenters to mention the following observations. Recently it was noted that gel chromatographic separations of the five fragments resulting from the degradation of cytochrome c by bromocyanogen became dependent on the batch number of the gel. This dependency concerns only separations of unprotected fragments, using 7% (v/v) formic acid as the eluent. The elution profile of protected compounds, which in turn run in 50% (v/v) formic acid, was unaffected.
Improved synthesis and resolution of β‐(3‐pyridyl)‐DL‐α‐alanine
Authors: FOLKERS KARL , KUBIAK TERESA , STEPINSKI JANUSZ
Published: August 2010

β‐Benzamido‐α‐(3‐pyridyl)‐DL‐α‐alanine hydrochloride was synthesized from 3‐pyridinecarboxyaldehyde via the azlactone which was hydrolyzed to the acrylic acid before hydrogenation. The methyl ester was effectively resolved with subtilisin. The optical purity of the D‐isomer was established, since the D‐isomer was used in synthesis of antagonists of the luteinizing hormone releasing hormone.
Cooperative interactions in neurophysin‐neuropeptide hormonecomplexes
Authors: ABERCROMBIE DAVID M. , KANMERA TATSUHIKO , ANGAL SAROJANI , TAMAOKI HIDETSUNE , CHAIKEN IRWIN M.
Published: August 2010

The structural interdependence between neurophysin (NP) self‐association and ligand binding surfaces has been studied by analytical affinity chromatography of several NP sequence variants and derivatives on Met‐Tyr‐Phe‐aminobutyl‐agarose and bovine NP‐II Sepharose. Elutions of radiolabeled NP's from both matrices show that hybrid dimers can form between major bovine NP's (I and II, or VLDV‐ and MSEL‐NP's, respectively), as well as between human and bovine NP's, with affinities close to that for homologous dimer formation. Such evidence supports the view that the region of NP involved in NP‐NP contact is composed primarily of conserved structural elements of the protein. NP antibodies which recognize surfaces close to or in the NP‐NP contact region have been detected by their effects on bovine NP‐II elution on NP‐II Sepharose. Elutions of [3‐nitro‐Tyr 49] BNP‐II from Met‐Tyr‐Phe‐aminobutyl‐agarose showed that nitration has little effect on the chromatographic properties of NP‐II. This evidence substantiates previous arguments (Angal, S. & Chaiken, I.M. (1982) Biochemistry 21, 1574–1580) that the chromatographic behavior of native NP's on the affinity matrices is an expression of the interdependence of NP self‐association and ligand binding surfaces and not due to bivalent peptide binding by NP monomer. The affinity chromatographic properties of NP derivatives, including bovine NP‐II photolabeled in the ligand binding site and tryptic fragments of bovine
Prokaryotic metallothionein
Authors: OLAFSON ROBERT W.
Published: August 2010

A unique metallothionein (MT) has been isolated from a Synechococcus sp. cyanobacterium by gel permeation and reverse phase high performance liquid chromatography. Although physiologically similar to well characterized eukaryotic MTs, amino acid analysis and amino terminal sequence determination show substantial differences. The cysteine content is 18% and the molecule contains 3 histidines, 2 tyrosines and 7 long chain aliphatics compared with approximately 32% cysteine content and none or very few of the latter three residues in eukaryotic compositions. On determination of 43% of the prokaryotic primary structure only the presence of Cys‐X‐Cys sequences indicated a structure similar to eukaryotic MTs and on alignment for maximum homology only 3 out of the 24 residues were identical when compared with any of 3 eukaryotic sequences. Allowing for conservative homologous replacements increased the homology to only 4 amino acids. Lack of association of serine and Iysine residues with cysteines in the sequenced portion of the bacterial MT, together with the previous distinctions, suggests major tertiary structure differences with eukaryotic MTs.
Are secondary structures secondary?
Authors: KOLASKAR A.S. , RAMBRAHMAM V.
Published: August 2010

Crystallographically observed secondary structures in globular proteins are divided into two categories based on calculated potential values for these structures. Type I secondary structures are those which have maximum potential in observed structural state. These type I structures consist of those amino acids which intrinsically prefer that structural state. On the other hand type II secondary structures have a calculated potential value which is not maximum for the observed state. Type II structures are composed of those amino acid residues which do not intrinsically prefer the observed state and thus seem to have been formed due to tertiary interactions. All the observed secondary structures have been identified as type I or type II in 31 different globular proteins considered. It is suggested that type II structures are formed at a latter stage of protein folding mainly due to favourable tertiary interactions.
Vibrational analysis of peptides, polypeptides, and proteins.
Authors: Naik Vaman M. , Krimm S.
Published: August 2010

A normal mode calculation has been done for Pro‐Leu‐Gly‐NH2 in its crystalline type II β‐turn structure, and assignments have been made to infrared and Raman bands of this molecule and its N‐deuterated derivative. Observed and calculated frequencies below 1700 cm‐1 agree to within about 6 cm‐1. This analysis provides a sound basis for studying the conformation dependence of the vibrational spectrum.
Chain‐length dependence for secondary structure formation of homo‐oligopep tides fromε‐tert.‐butyloxycarbonyl‐L‐lysine with a lipophilic C‐terminal group
Authors: Toniolo Claudio , Bonora Gian Maria , Lüscher Immanuel F. , Schneider Conrad H.
Published: August 2010

A solid‐state and solution analysis of the homo‐oligopeptides from ε‐tert.‐butyloxycarbonyl‐L‐lysine with p‐oxymethylbenzylcholestan‐3β‐yl succinate as C‐terminal group, using infrared absorption and circular dichroism, is described. The occurrence of intermolecular β‐structure is seen in the solid state and in solvents of low polarity, e.g. methylene chloride, for peptides of intermediate size (from pentamer to decamer). Conversely, the eicosapeptide exhibits a high percentage of α‐helical structure both in the solid state and in 2, 2, 2‐trifluoroethanol. The influence of the C‐terminal group on the conformational preferences of the ε‐blocked homo‐oligolysines in the solid state and in organic solvents appears negligible.
Photoreactive derivative of Kunitz's soybean trypsin inhibitor.
Authors: Ramachandran J. , Smirnoff Patricia , Birk Yehudith
Published: August 2010

The photoreactive arylsulfenyl chloride 2‐nitro‐4‐azidophenylsulfenyl chloride (2,4‐NAPS‐Cl) has been used for the selective modification of tryptophan in Kunitz's soybean trypsin inhibitor (SBTI). The ultraviolet absorption spectrum and amino acid analysis of 2,4‐NAPS‐SBTI indicated that only one of the two tryptophans (93 or 117) present in SBTI was modified. CNBr cleavage of 2,4‐NAPS‐SBTI resulted in two fragments 1–114 and 115–181.Amino acid analysis of the two separated fragments showed that only tryptophan 93 underwent modification. 2,4‐NAPS‐SBTI fully retained its inhibitory activity against trypsin. The photoaffinity labeling of trypsin with 2,4‐NAPS‐Cl was performed on tritiated trypsin prepared by reacting bovine trypsin with [3H]‐succinimidyl propionate. The covalent attachment of 2,4‐NAPS‐SBTI to the tritiated trypsin after photolysis was demonstrated by exclusion chromatography on Sephadex G‐50 in the presence of guanidine hydrochloride.
Influence of sarcosine or N‐methylalanine in position 7 on the antagonistic properties of [1‐deaminopenicillamine]‐ and [1‐(β‐mercapto‐β, β‐cyclopentylmethylene‐propionic acid)]‐vasopressin
Authors: Gazis Diana , Schwartz Irving L. , Lammek B. , Grzonka Zbigniew
Published: August 2010

Substituting sarcosine or N‐methylalanine for proline in the inhibitory vasopressin analogs dPAVP and d(CH2)5AVP had the following effects: 1) milk ejection and antidiuretic activities were severely depressed, 2) pressor antagonism was maintained but weakened somewhat, and 3) antagonism in the uterus in vitro was maintained, but no consistent pattern was seen.
Pyrrolidine ring conformations in prolyl peptides from 13C spin‐lattice relaxation times
Authors: Shekar S.C. , Sankaram M.B. , Easwaran K.R.K.
Published: August 2010

A method was developed in the framework of a bistable jump model to obtain the pyrrolidine ring conformations in proline peptides from 13C spin‐lattice relaxation times. Equations are presented expressing the ring torsions in terms of the 13C spin‐lattice relaxation times of the ring carbons. This method was applied to 26 pyrrolidine ring systems and acceptable conformations were obtained.
Effect of N‐terminal iodination on the biological, immunological and receptor binding properties of secretin.
Authors: Izzo Richard S. , Praissman Melvin
Published: August 2010

Both radiotrace labeled and high specific activity 125I‐labeled derivatives of secretin were prepared by direction iodination of the histidyl residue with chloramine T ([125I] secretin) and by conjugation of a preiodinated Bolton‐Hunter group (iodo‐3‐(4‐hydroxyphenyl) propionate) to the free α‐amino group at the N‐terminus ([125I] BH‐secretin). Following purification, the biological, immunological and receptor binding properties of both secretin derivatives were compared. [125I] secretin and [125I] BH‐secretin were equally effective in a sensitive radioimmunoassay that detected secretin and secretin (5–27) but not CCK‐8, VIP and glucagon. Although both derivatives retained 60% of the biological potency of secretin as measured by cAMP accumulation in pancreatic acinar cells, only the directly iodinated peptide ([125I] secretin) could be used to characterize specific binding sites on rat pancreatic membranes. The N‐terminal blocked derivative ([125I] BH‐secretin) in contrast dissociated rapidly from pancreatic membranes reflecting an unstable hormone‐receptor complex. These results suggest that a free α‐amino group at the N‐terminus may be essential for an optimal interaction of secretin with its pancreatic receptor.
Preparation and properties of Nα‐trityl amino acid 1‐hydroxybenzotriazole esters
Authors: Barlos Kleomenis , Papaioannou Dionysios , Theodoropoulos Dimitrios
Published: August 2010

N
α‐Trityl amino acid 1‐hydroxybenzotriazole active esters, in contrast to HOBt esters of other protected amino acids, exhibit high hydrolytic stability and can be isolated in excellent yields and purity. The derivatives occur in three isomeric forms (an ester=I, two amides=II and III). All active ester forms react at high concentrations within 2 h with various alkyl amino acid esters to produce the corresponding protected dipeptides in high yields. Amorphous active esters on prolonged storage at — 20° rearrange partially towards form III without any sign of decomposition.
Syntheses and properties of tertiary peptide bond‐containing polypeptides.
Authors: Narita Mitsuaki , Fukunaga Tsutomu , Wakabayashi Atsushi , Ishikawa Kazunori , Nakano Hirofumi
Published: August 2010

Oligo(Leu)s containing Pro or (Dmob) Leu residues were prepared by the stepwise elongation and fragment condensation methods. The peptides prepared were the following: Boc‐Leun‐OBzl (n = 3–6 and 9), Boc‐Pro‐Leu3‐OBzl, Boc‐Leun‐Pro‐OBzl (n = 3–5), Boc‐Leun‐Pro‐Leu3‐OBzl (n = 3 and 4), Boc‐(Leu4‐Pro)2‐OBzl, Boc‐Leu3‐Pro‐Leun‐Pro‐Leu3‐OBzl (n = 6 and 7), Boc‐Leu3‐Gly‐(Dmob) Leu‐OMe, Boc‐[Leu3‐Gly‐(Dmob) Leu‐Leu3]n‐OBzl (n = 1 and 2). The insertion of the Pro and Gly‐(Dmob) Leu residues into a peptide chain caused “the peptide segment separation” and achieved remarkable solubility improvement of N‐ and C‐protected oligo(Leu) derivatives in a variety of organic solvents. The conformations of typical peptides in the solid state and in DMSO were also investigated using i.r. spectroscopy. The incorporation of tertiary peptide bonds in a central position of the β‐sheet structure induces the onset of an unordered structure in the solid state. In DMSO, peptides are efficiently subjected to solvation to have the unordered structure.
In vitrointeraction of opioid peptides with phospholipids.
Authors: Cherubini Ornella , De Marco Valeria , Roscetti Gianna , Possenti Roberta , Roda L. Giorgio
Published: August 2010

Interaction of Leu‐ and Met‐enkephalin with phosphatidylserine has been studied by chromatographic and spectrophotometric techniques. The main results of our investigation may be summarized as follows: i) Both enkephalins bind to phosphatidylserine; ii) no difference between the two enkephalins is noticeable; and iii) with both peptides the binding phenomenon leads to the formation of two complexes with a definite stoichiometry which are sterically much smaller than the original vesicles. On the basis of the submitted data, a tentative model of the newly formed complexes is provided.
Physicochemical properties of maltosyl and glucosaminyl derivatives of beta‐lactoglobulin
Authors: Waniska Ralph D. , Kinsella John E.
Published: August 2010

Maltosyl and glucosaminyl derivatives of beta‐lactoglobulin (b‐LG) were analyzed for their physicochemical properties: reduced viscosity, ultraviolet difference spectra, intrinsic fluorescence, hydrophobicity and circular dichroism. The viscosity of these derivatives increased as the mass of the carbohydrates covalently linked to b‐LG increased. The ultraviolet difference spectra and the intrinsic fluorescence of these proteins revealed that the microenvironments of aromatic amino acid residues of b‐LG were increasingly exposed to the surface of the protein as the extent of modification increased; and the polarity of these residues also increased as modification increased. The hydrophobicities of M‐b‐LG derivatives decreased as the extent of modification increased while the hydrophobicities of G‐b‐LG derivatives were relatively unchanged. The circular dichroic analysis of these proteins indicated that the ordered secondary structures of the extensively modified derivatives of b‐LG were partially unfolded. Thus, the carbohydrates covalently linked to b‐LG altered many physiochemical properties. These physicochemical changes of b‐LG apparently resulted from an alteration of forces stabilizing the structure of the protein.
Synthetic analogues of the proteinase inhibitor: chymostatin
Authors: Galpin I.J. , Wilby A.H. , Place G.A. , Beynon R.J.
Published: August 2010

Putative proteinase inhibitors with the general structure Z. Arg. X.Phe.H (where X = Leu, Ile or Val) were prepared by solution synthesis using semicarbazone protection for the aldehyde function. These inhibitors showed strong activity towards chymotrypsin whereas the semicarbazones and dipeptides aldehydes showed considerably reduced activity. The structural requirements for inhibition would seem to mimic those of the natural chymotrypsin inhibitor chymostatin.
Isolation and characterization of a genetic variant of bovine proinsulin
Authors: Frank Bruce H. , Pekar Allen H. , Pettee James M. , Schirmer Elmer M. , Johnson Melvin G. , Chance Ronald E.
Published: August 2010

A genetic variant of bovine proinsulin has been isolated using preparative reverse‐phase HPLC. The new proinsulin (bovine proinsulin II) differs from the known proinsulin (bovine proinsulin I) by a single amino acid residue at position C‐48 in the connecting peptide. The amino acid replacement is a leucine substitution for proline. The two proinsulins were found in a ratio of approximately 9:1, proinsulin I: proinsulin II. No chemical or biological differences were observed for the two proinsulins other than their different elution times on reverse‐phase HPLC.
Antidiuretic and pressor activities of vasopressin analogs with L‐alaninamide and D‐alaninamide substitutions at position 9
Authors: Buku Angeliki , Gazis Diana , Schwartz Irving L.
Published: August 2010

Analogs of arginine vasopressin (AVP) and lysine vasopressin (LVP) — with an L‐alaninamide residue or a D‐alaninamide residue replacing the naturally occurring glycinamide in position 9 — lose virtually all pressor activity but retain from 10 to 70% of the antidiuretic activity of their parent hormones. These findings, in conjunction with the data of others on the biological consequences of alterations in positions 7 and 8, show that the antidiuretic receptor will tolerate considerably more structural alteration in the C‐terminal tripeptide “tail” of the vasopressins than will the pressor receptor.
Importance of methionine residues in the enzymatic carboxylation of biotin‐containing peptides representing the local biotinyl site of E. coli acetyl‐CoA carboxylase
Authors: KONDO HIROKI , UNO SHINGO , KOMIZO YOSHIYUKI , SUNAMOTO JUNZO
Published: August 2010

A biotin‐containing hexapeptide Ac‐Glu‐Ala‐Met‐Bct‐Met‐Met (1) that represents the local biotin‐containing site of Escherichia coli acetyl‐CoA carboxylase has been prepared by the solid phase method. Peptide 1 is carboxylated by the biotin carboxylase subunit dimer of E. coli acetyl‐CoA carboxylase with the following kinetic parameters; Km 12 mm, Vmax 2.8 μm· min–1. These compare with the parameters for biotin of Km 214 mm and Vmax 28 μm· min–1. Hence, the overall reactivity (Vmax/Km) of 1 is 1.8 times greater than that of free biotin. When all methionines in 1 are replaced by alanine, the resulting peptide (2) retains a similar binding ability but with a much decreased Vmax. It was also found that peptide 3, which carries an N‐benzyloxy carbonyllysine in place of biocytin in 1, decreases the Km of biotin threefold.
Synthesis of cyclic and acyclic partial retro‐inverso modified enkephalins
Authors: BERMAN JUDD M. , GOODMAN MURRAY
Published: August 2010

The cyclic partial retro‐inverso modified enkephalins, H‐Tyr‐cyclo[‐D‐Glu‐Gly‐gPhe‐D‐Leu‐] (I), H‐Tyr‐cyclo[‐D‐A2bu‐Gly‐gPhe‐R&S‐mLeu‐] (IIf, IIs), and H‐Tyr‐cyclo[‐D‐Glu‐Gly‐Phe‐gLeu‐] (III), have been synthesized by solution methodology. In a like manner, their corresponding acyclic analogs Ia‐IIIa containing D‐Ala2 have also been prepared. Gem‐diaminoalkyl residues were generated by conversion of Boc‐dipeptide carboxamide to the corresponding gem‐diaminoalkyl “dipeptide” salt using [bis(trifluoroacetoxy)iodo] benzene. Cyclizations were achieved at high dilution utilizing diphenylphosphoryl azide as the coupling reagent.
Structure and conformation of linear peptides
Authors: LALITHA V. , SUBRAMANIAN E. , BORDNER J.
Published: August 2010

The tripeptide, glycyl‐glycyl‐L‐valine, crystallizes as a dihydrate in the monoclinic space group P21, with a = 5.786(1), b = 7.954(2), c = 14.420(3)A, β= 93.85(2)d̀, Z = 2. The structure was solved by direct methods and refined to an R‐value of 0.040 for 876 observed reflections. The molecule exists as a zwitterion in the crystal. The peptide planes show significant deviations from planarity. The chain conformation resembles a reverse turn if the orientation of the carboxyl group is also taken into account. An intramolecular water bridge links the amino and carboxyl ends of the molecule. The crystal packing involves spatial segregation of polar and nonpolar moieties.
Conformation and hydrogen bonding of N‐formylmethionyl peptides
Authors: CHATTERJEE A. , PARTHASARATHY R.
Published: August 2010

Crystals of N‐formyl‐L‐methionyl‐L‐valine (C11 H20 N2 O4S, M.W. = 276.3) are orthorhombic, space group P2 1 21 21 with cell constants at 294K of a = 4.851 (1), b = 14.925 (1), c = 19.745 (3) Å, V = 1429.8 (1) Å3, Z = 4 and observed (Dm) and calculated (Dx) of 1.49 and 1.488 g° cm‐3, respectively. The crystal structure was solved using automatic diffractometer data (1260 reflections ← 3s̀) and refined to a final R‐value of 0.035. This structure contains a short (2.626 (3) Å) intermolecular hydrogen bond between the carboxyl OH and the N‐acyl oxygen, a feature common to most N‐acylamino acids and N‐acylpeptides. The peptide is nearly planar (ω= 174.6 (5)); the values of ø1, ø2, øT1 and øT2 are, respectively, 131.8 (4)d̀, ‐130.9 (5)d̀, ‐39.3 (4)d̀ and 142.1 (4)d̀. The methionine side chain is not zig‐zag transplanar; the side chain torsion angles are: χ11=‐60.0 (4)d̀, χ12= 176.0 (4)d̀ and χ13= 71.8 (4)d̀. The two Cγ'sfor valine have χ1‐values of ‐64.4 (5)d̀ and 173.7 (5)d̀. The formation of the parallel rather than antiparallel β‐sheet structure, the participation of the N‐formyl group in the parallel β‐sheet and the use of C‐H. O hydrogen bonds to stabilize the β‐sheet are novel features found in this structure.
Synthesis of the Mg antigenic determinant and peptide analogs related to human glycophorin A
Authors: FERRARI B. , PAVIA A.A.
Published: August 2010

The Mg antigen is a well known rare mutation of the MN blood group system. The amino‐terminal pentapeptide related to human glycophorin Amg, Leu‐Ser‐Thr‐Asn‐Glu, as well as pentapeptides representing the peptide backbone of glycophorin AM, AN and AMc and other analogs, were synthesized to serve both as glycosyl transferase acceptors and as artificial antigens. These compounds were obtained by a stepwise peptide coupling strategy in solution.
Association‐dissociation of histone oligomers
Authors: MAÑOSA JOAN , PALAU JAUME , LAWRENCE JEAN‐JACQUES
Published: August 2010

The spin label method has been used to obtain information about conformational changes of histone oligomers taking advantage of the fact that at a low ionic strength and in the presence of other histones about 45% of cysteine residues of histone H3 react with the 3‐maleimido‐2,2,5,5‐tetramethyl‐l‐pyrrolidinyloxyl spin label. For the labeled complexes H3‐H4 and Hn̈ the degree of immobilization of the spin label is a function of the ionic strength. This variation is identical for both complexes within a long range of ionic strengths, including the interval of 0.8‐2 M NaCI, under which conditions interactions are known to exist between the tetramer (H3)2 (H4)2 and the dimer (H2A) (H2B). This finding suggests a negligible influence of the dimer for modifying the cysteine residue environment of histone H3 on octamer formation. GuHCI treatment at high ionic strength of the labeled complexes gives rise to a non‐lineal increase in the degree of mobility of the spin label. This increase, at low GuHCI concentration (0‐0.5 M GuHCI), is interpreted as showing a lowering in rigidity for the Cys residue environment, without affecting the general stability of the tetramer (H3)2 (H4)2. At higher GuHCI concentration (2–3 M GuHCI) the increase in the spin label mobility is related to a dissociation of the complexes in single histones. Our results are consistent with the view that the overall structure of the tetramer, as well as its conformational changes during complex structuration or denaturation, are not strongly affected by the presence of the dimer (H2A) (H2B).