bluuebunny/crossref_metadata_2025 huggingface dataset:
SYNTHESIS AND BIOLOGICAL ACTIVITIES OF [7‐(AZETIDINE‐2‐CARBOXYLIC ACID)]‐OXYTOCIN AND ‐LYSINE‐VASOPRESSIN
Authors: BARBER MARY , JONES JOHN H. , STACHULSKI ANDREW V. , BISSET GORDON W. , CHOWDREY HARDIAL S. , HUDSON ALAN L.
Published: August 2010

[7‐(Azetidine‐2‐carboxylic acid)]‐oxytocin and ‐lysine‐vasopressin have been synthesised by a (6 + 3) strategy using protected hexapeptide acids with preformed disulphide bridges, and their biological activities have been investigated. All activities were reduced but not to the same extent. In assays of pressor and antidiuretic activity it was observed consistently that the responses to the vasopressin analogue were of shorter duration than responses to lysine‐vasopressin of the same amplitude.
CONFORMATIONAL ANALYSIS OF THE RIGHT‐HAND TWISTED ANTIPARALLEL β‐STRUCTURE
Authors: RAGHAVENDRA K. , SASISEKHARAN V.
Published: August 2010

The conformational analysis of a pair of two‐linked peptide units in the anti‐parallel arrangement is reported here with a view to study the effect of association of one chain with the other. The pair of two‐linked peptide units were fixed in space through the hydrogen bonds between them, in accordance with certain hydrogen bond criteria. Model building was undertaken to ascertain whether the proximity of the side‐chains could be used to eliminate any one of the right‐hand twisted, left‐hand twisted or regular β‐structures. Stereochemically, it was found possible with all of them. The preference for a right‐hand twisted β‐structure, however, was indicated by the classical energy calculations. The relevance of the results thus obtained is discussed in the context of the preferential right‐hand twist of the β‐pleated sheets present in globular proteins. The agreement between the minimum energy conformations obtained for the pair of two‐linked peptide units and the globular protein data is also indicated.
MINIMAL SIDE‐CHAIN PROTECTION CAN BE A SUCCESSFUL STRATEGY IN SOLID‐PHASE PEPTIDE SYNTHESIS
Authors: COY DAVID H. , BRANYAS NANCY
Published: August 2010

The N‐terminal tyrosine residue of Met‐enkephalin could be readily incorporated without protection of its phenolic hydroxyl group. Furthermore, the HF‐cleaved product contained fewer impurities than that derived from hydroxyl‐protected material. Despite the presence of Tyr in the center of the chain, an LH‐RH antagonist, [d‐Phe2, d‐Trp3, d‐Phe6]‐LH‐RH, could also be made in normal yield by incorporation of free Boc‐Tyr. Syntheses of the same model peptide without protection of the Ser residue and protection of the Arg residue as the guanidine HCl salt also gave excellent yields of analog. Finally, the LH‐RH inhibitor and a highly active agonist, [d‐Leu6, desGly‐NH210]‐LH‐RH ethylamide, were synthesized without protection of Tyr, Ser and Arg, which enabled free peptides to be generated directly by ammonolysis and ethylaminolysis, respectively, without HF treatment. In all examples, no evidence emerged to suggest reaction of side‐chains during synthesis.
FORMATION AND SYNTHESIS OF 3‘‐t‐BUTYLTYROSINE
Authors: LUNDT B.F. , JOHANSEN N.L. , MARKUSSEN J.
Published: August 2010

During acidolysis by TFA of the t‐butyl protecting group from Z‐Tyr(But) or from Ser(But) in the presence of tyrosine, C‐t‐butylation occurred in the aromatic nucleus in Z‐Tyr or tyrosine, respectively, to an extent of 0.5–1.0%. CF3COOBut formed during the acidolysis slowly C‐t‐butylates tyrosine. Tyr(3'But) is formed. The synthesis of Tyr(3'But) · HCl is described.
PREPARATION OF RACEMIC 2r‐CARBOXY‐TRANS, TRANS‐3, 4‐DIDEUTERO‐PYRROLIDINE (DL‐TRANS, TRANS‐3, 4‐DIDEUTERO‐PROLINE) AND UNAMBIGUOUS ASSIGNMENT OF PROTONS IN THE 1H N.M.R. SPECTRUM OF PROLINE
Authors: ANTEUNIS MARC J. O. , BORREMANS FRANS A. M. , BECU CHRISTIAN , SLEECKX JEF
Published: August 2010

Racemic trans, trans‐3,4‐dideutero proline has been prepared by catalytic deuteration of 3‐pyrroline‐2‐carboxylic acid. The stereospecificity of the reduction (i.e. trans to the carboxylic group) was ascertained after transformation of the dideutero compound into the diketopiperazide c/Pro, Aib/, for which unambiguous proton assignments in the 1H n.m.r. spectrum had been obtained previously. The identification of the configuration of the dideutero‐proline allows for the affirmation of the correctness of proton assignments as previously proposed in literature.
EXTENSIVE MODIFICATION OF PROTEIN AMINO GROUPS BY REDUCTIVE ADDITION OF DIFFERENT SIZED SUBSTITUENTS
Authors: FRETHEIM KRISTEN , IWAI SHIGEO , FEENEY ROBERT E.
Published: August 2010

The amino groups of ovomucoid, lysozyme and ovotransferrin have been extensively alkylated by reacting the proteins with various carbonyl reagents in the presence of sodium borohydride. The extent of modification ranged from 40 to 100%. Essentially monosubstitution was obtained with acetone, cyclopentanone, cyclohexanone and benzaldehyde, while 20–50% disubstitution was obtained with N‐butanal and nearly 100% disubstitution was obtained with formaldehyde. Both the methylated and isopropylated derivatives of all three proteins were soluble and retained almost full biochemical activities, but introduction of the larger substituents caused precipitation with lysozyme and ovotransferrin.
SYNTHESIS OF γ‐CARBOXYGLUTAMIC ACID AND ITS DERIVATIVES VIA MANNICH‐BASE CONDENSATION
Authors: JUHÁSZ ATTILA , BAJUSZ SÁNDOR
Published: August 2010

This report describes the synthesis of Nα‐formyl and Nα‐benzyloxycarbonyl‐γγ‐di‐t‐butyl‐γ‐carboxyglutamic acid via Mannich‐base condensation starting from di‐t‐butyl malonate and diethyl formamido or benzyloxycarbonylamidomalonate.
RELATIONSHIP BETWEEN MUTABILITY, POLARITY AND EXTERIORITY OF AMINO ACID RESIDUES IN PROTEIN EVOLUTION
Authors: GO MITIKO , MIYAZAWA SANZO
Published: August 2010

A systematic study was carried out on mutability of amino acid residues in evolving proteins in relation to their polarity and location within three‐dimensional structure of proteins. Exteriority of residue sites is quantitatively defined as accessibility based on their static accessible surface area to solvent water molecule. Residue sites are classified into interior and exterior depending on their accessibility. More frequent substitution on exterior sites is confirmed to be general in eight sets of homologous protein families regardless of their biological functions and of presence or absence of a prosthetic group. Virtually all types of amino acid residues are found to have higher mutabilities on the exterior than in the interior. No correlation between mutability and polarity was observed of amino acid residues in the interior and on the exterior, respectively. Amino acid residues are classified into three depending on their polarity, polar (Arg, Lys, His, Gln, Asn, Asp and Glu), weak polar (Ala, Pro, Gly, Thr and Ser) and nonpolar (Cys, Val, Met, Ile, Leu, Phe, Tyr and Trp). Amino acid replacements during protein evolution are very conservative; 88% and 76% of them in the interior and on the exterior, respectively, are within the same group of the three. Inter‐group replacements are such that weak polar residues are replaced more often by nonpolar residues in the interior and more often by polar residues on the exterior.
SPOROPOLLENIN
Authors: MACKENZIE GRAHAME , SHAW GORDON
Published: August 2010

Sporopollenin from Lycopodium clavatum has been found to be capable of acting as a solid support for peptide synthesis. It is stable to chloromethylation and to the standard deblocking procedures and its constant mesh size, ready commercial availability, and constant molecular structure give it potential important practical advantages over synthetic resins.
REACTION OF BOVINE PANCREATIC RIBONUCLEASE A WITH 6‐CHLOROPURINE RIBOSIDE 5‘‐MONOPHOSPHATE
Authors: PARÉS XAVIER , PUIGDOMÉNECH PERE , CUCHILLO CLAUDI M.
Published: August 2010

The n.m.r. spectra of native S‐peptide and of S‐peptide II, a derivative obtained after reaction of bovine pancreatic ribonuclease A with 6‐chloropurine riboside 5′‐monophosphate, both in D2O and in urea‐d4, were obtained with a 270 MHz Fourier transform spectrometer. From these spectra it was possible to assign most of the proton resonances of the peptide and the position of the labelling group, the α‐NH2 of Lys‐1, was also deduced.
HUMAN β‐ENDORPHIN: SYNTHESIS AND CHARACTERIZATION OF ANALOGS IODINATED AND TRITIATED AT TRYOSINE RESIDUES 1 AND 27
Authors: HOUGHTEN RICHARD A. , CHANG WEN‐CHANG , LI CHOH HAO
Published: August 2010

Three tritiated analogs of human β‐endorphin have been prepared from their corresponding iodinated analogs. The iodinated analogs (diiodotyrosine at positions 1, 27 or 1 and 27) were synthesized by the solid‐phase method and were found to have biological and physical properties which were altered when compared with the native molecule. Catalytic exchange of these iodinated analogs in the presence of tritium yielded tritiated human β‐endorphins having full biological activity and specific activity of 50–100 Ci/mmol. Both the iodinated and tritiated β‐endorphin analogs were shown to be homogeneous by chromatography on carboxymethylcellulose, partition chromatography, paper chromatography, amino acid analysis, electrophoresis, high performance liquid chromatography, and isoelectric focusing on polyacrylamide.
(L‐2‐HYDROXY‐3‐MERCAPTOPROPIONIC‐ACID)OXYTOCIN
Authors: BRESLOW ESTHER , STAHL GLENN L. , WALTER RODERICH
Published: August 2010

The role of the α‐amino group of oxytocin in affecting the conformation of oxytocin and its binding to neurophysin was studied by a comparison of the circular dichroism and binding properties of oxytocin with those of (L‐2‐hydroxy‐3‐mercaptopropionic acid)oxytocin which contains a hydroxyl in place of the oxytocin amino group. The circular dichroism properties of (L‐2‐hydroxy‐3‐mercaptopropionic acid)oxytocin were very similar to those of deamino‐oxytocin (in which the amino group of oxytocin is replaced by a hydrogen) but differed significantly from those of oxytocin, particularly under conditions in which the oxytocin α‐amino group is protonated. The protonated oxytocin α‐amino group is known to participate in a salt‐bridge with a neurophysin carboxyl at neutral pH, but oxytocin appears to bind to neurophysin without salt‐bridge formation below pH 2. Nonetheless, (L‐2‐hydroxy‐3‐mercaptopropionic acid)oxytocin, like deamino‐oxytocin, was found not to bind to the hormone‐binding site of neurophysin with measurable affinity at either neutral pH or low pH. The results indicate that, in the binding of oxytocin to neurophysin, the protonated oxytocin α‐amino group plays a role more complex than that of carboxylate charge neutralization and suggest that this role involves an effect on oxytocin conformation. However, highly specific bonding interactions between the α‐amino group and neurophysin, additional to those of salt‐bridge formation, are not precluded.
CONFORMATIONAL STUDIES OF SOMATOSTATIN AND SELECTED ANALOGUES BY RAMAN SPECTROSCOPY
Authors: HAN SHAW‐LIN , RIVIER JEAN E. , SCHERAGA HAROLD A.
Published: August 2010

Laser Raman spectroscopy has been used to study the conformations of somatostatin and some selected analogues in aqueous solution. The results indicate that the CS‐SC dihedral angles of somatostatin and of these analogues (except [Ala3,14]‐SS, which has no disulfide bond) are within 20° of ± 85°, and the SS‐CC dihedral angles are predominantly in the range of 50° ‐ 180°. Furthermore, from the behavior of the amide I' and amide III bands, it appears that somatostatin adopts a β‐pleated sheet structure, whereas its analogues are less ordered (to varying degrees).
ISOLATION AND STRUCTURE OF ANOTHER β‐MELANOTROPIN FROM SALMON PITUITARY GLANDS
Authors: KAWAUCHI HIROSHI , ADACHI YASUSHI , ISHIZUKA BUNSHIRO
Published: August 2010

A heptadecapeptide has been isolated from a side fraction of β‐MSH in an acid acetone extract of the pituitary of the salmon, Oncorhynchus keta. The sequence analysis revealed the peptide to be another form of salmon β‐MSH with following primary structure; H‐Asp‐Gly‐Ser‐Tyr‐Arg‐Met‐Gly‐His‐Phe‐Arg‐Trp‐Gly‐Ser‐Pro‐Thr‐Ala‐Ile‐OH. The findings of two distinctive β‐MSHs as well as two endorphins as reported previously in the pituitary extract suggest that the teleost pituitary may secrete two different precursor molecules, β‐LPH, and thus also higher molecular weight precursors.
STUDY OF THE STATE OF IONIZATION OF [LEU5]‐ENKEPHALIN IN THE CRYSTAL AND IN SOLUTION
Authors: HAN S. L. , STIMSON E. R. , MAXFIELD F. R. , LEACH S. J. , SCHERAGA H. A.
Published: August 2010

The state of ionization of [Leu5]‐enkephalin in the crystal and in solution was studied with the aid of Raman, i.r., and n.m.r. techniques. The results indicate that, in the crystal, enkephalin adopts the dipolar ion form. In water near neutral pH, enkephalin also exists in the dipolar ion form whereas in DMSO‐d6 it is a mixture of the dipolar ion and uncharged species. The pK's of α‐amino and α‐carboxyl groups are probably closer to each other in DMSO than in H2O.
ISOLATION AND AMINO ACID COMPOSITION OF SAUVAGINE
Authors: MONTECUCCHI PIER CARLO , ANASTASI ADA , de CASTIGLIONE ROBERTO , ERSPAMER VITTORIO
Published: August 2010

The skin of the South American frog Phyllomedusa sauvagei contains a new active polypeptide, sauvagine, which does not belong to any of the peptide families hitherto described in the amphibian skin. Sauvagine was isolated in a pure form starting from crude methanol extracts. The purification procedure involved several successive steps: dialysis, precipitation with ethanol and acetone, gel filtration and ion exchange chromatography. Two forms of sauvagine were separated. The major component (sauvagine I) was submitted to acid hydrolysis. The sauvagine molecule appeared to possess clear hydrophobic characteristics and to consist of a straight chain of 40 amino acid residues, among which the glutamyl‐, aspartyl‐ leucyl‐ and isoleucyl‐residues were particularly well represented. The elucidation of the amino acid sequence in the sauvagine molecule is in progress.
N.M.R. AND EQUILIBRIUM DIALYSIS STUDIES OF THE INTERACTION OF BOVINE NEUROPHYSIN‐I WITH VASOPRESSIN AND SMALL PEPTIDES
Authors: BOTHNER‐BY AKSEL A. , LEMARIE BERNARD , WALTER RODERICH , CO ROCHESTER TIAO‐TE , RABBANI LILLIAN D. , BRESLOW ESTHER
Published: August 2010

The binding to bovine neurophysin of lysine‐vasopressin and of lysine‐vasopressin selectively deuterated at the protons ortho to the tyrosine hydroxyl was studied by proton n.m.r. and equilibrium dialysis. The principal object of these studies was to investigate reports that, at standard salt concentrations, neurophysin contained a second site specific for vasopressin. At pH 6, the effects of neurophysin‐I on the line‐width, longitudinal relaxation rate and nuclear Overhauser properties of the lysine‐vasopressin tyrosine ring protons were interpretable in terms of a slow‐exchange 1:1 interaction between lysine‐vasopressin and neurophysin. Additionally, n.m.r. competition studies between lysine‐vasopressin and L‐phenylalanyl‐L‐tyrosinamide suggested 1:1 competition for a single binding site on neurophysin. No evidence pointing to a significant second lysine‐vasopressin‐binding site was obtained from the n.m.r. studies. The lack of a moderately strong second binding site for lysine‐vasopressin at neutral pH was also indicated by equilibrium dialysis studies at relatively high free hormone concentrations. These studies demonstrated only a single thermodynamically significant site for either oxytocin or vasopressin and failed to confirm a reported effect of LiCl on the number of sites available to oxytocin. It is suggested that secondary sites for the hormones are probably markedly weaker and less specific than reported elsewhere.
STOPPED‐FLOW INVESTIGATION OF NITRATED BOVINE NEUROPHYSIN MONOMER BINDING TO OXYTOCIN
Authors: PEARLMUTTER A. FRANCES , DALTON ELLEN J.
Published: August 2010

By use of stopped‐flow kinetic data, we have measured the kinetics of mononitrated neurophysin I monomer binding to oxytocin. The association rate constant was 1.3(±0.3) × 105 M‐1 s‐1 and the dissociation rate constant was 2.0 (± 0.5)s‐1 for protonated oxytocin binding. Both rates are significantly slower than those observed for neurophysin dimer. These data suggest that the binding process by which the monomer binds oxytocin is not identical to that of dimer.
PRIMARY STRUCTURE OF LOBSTER‐MUSCLE ARGININE KINASE: Amino and Carboxyl‐terminal Structure of the Enzyme and Complete Alignment of the Cyanogen‐Bromide Peptides
Authors: REGNOUF FRANÇOISE , KASSAB RIDHA , DEBUIRE BRIGITTE , RICHARD CLAUDE , HAN KIA‐KI
Published: August 2010

The acetylation state of the blocked NH2‐terminal end of arginine kinase was characterized by the occurrence of 1 mol acetyl group/mol protein; a 5‐residue segment corresponding to the amino‐terminal portion was isolated from a pronase digest of the enzyme and its amino acid sequence determined as N‐acetyl Ala‐Asx‐Ala‐Ala‐Thr.

Arginine kinase is terminated at the carboxyl end by the sequence Lys‐Glu‐MetOH; this particular 3‐residue sequence is repeated three times in the overall structure of the protein and is present in three CNBr fragments. One of these, a peptide of 14 amino acid residues, was identified in the course of this study and its amino acid sequence determined. Its location at the COHO‐terminal end of the enzyme was recognized on the basis of investigations carried out with des‐MetOH‐Glu‐arginine kinase, a specific proteolytic derivative.

The alignment of the eight CNBr‐fragments which constitute the arginine kinase molecule was established according to the sequential and compositional properties of seven unique tryptic methionyl peptides isolated from the whole protein. The alignment was confirmed by using BNPS‐skatole fragments of the enzyme as another protein source.
β‐ENDORPHIN: SYNTHESIS AND RADIOLIGAND BINDING ACTIVITY OF ANALOGS CONTAINING CYSTINE BRIDGES
Authors: BLAKE JAMES , FERRARA PASCUAL , LI CHOH HAO
Published: August 2010

Two analogs of human β‐endorphin containing cystine bridges between positions 21 and 26 or 14 and 26 have been synthesized and their radioligand binding activity using rat brain membranes has been determined. Both peptides showed three to four times the binding activity of human β‐endorphin.
SUBTILISIN: FAST AND SLOW PROTEOLYSIS OF PEPTIDE BONDS OF OXIDIZED A CHAIN OF INSULIN
Authors: MONTALI U. , LUCACCHINI A. , RONCA G. , ROSSI C.A.
Published: August 2010

Insulin performic acid‐oxidized A chain was digested with subtilisin type Carlsberg. The kinetics of proteolysis was studied and the bonds split with fast and with slow reactions were identified. The most susceptible bonds are CySO3H 11‐Ser 12 and Leu 13‐Tyr 14. Three bonds are hydrolyzed at a slower rate: Leu 16‐Glu 17, Asn 18‐Tyr 19 and Tyr 19‐CySO3H 20.
COMPUTER‐AIDED SEQUENCING OF A PROTEIN FROM THE MASSES OF ITS CONSTITUENT PEPTIDE FRAGMENTS
Authors: KITAGISHI TOYOKO , HONG YEONG‐MAN , SHIMONISHI YASUTSUGU
Published: August 2010

A computer program was designed for determining candidate sequences of polypeptides and proteins from the molecular weights and N‐terminal partial sequences of the peptide fragments derived from the polypeptides and proteins by specific cleavages. The basic principle for sequencing a protein by this method is described.
CONFORMATIONAL STABILITY OF PORCINE‐PANCREATIC SECRETORY TRYPSIN INHIBITORS (KAZAL INHIBITORS)
Authors: MENEGATTI E. , TOMATIS R. , GUARNERI M. , SCATTURIN A.
Published: August 2010

The presence of secondary structure and the strong conformational resistance of porcine pancreatic trypsin inhibitors (Kazal inhibitors) PSTI I and PSTI II to denaturant agents have been investigated by circular dichroism (CD) and fluorescence measurements. These proteins heated for 6 h at 85° are still highly active.
PREPARATION OF TRITIATED α‐MELANOTROPIN WITH HIGH SPECIFIC RADIOACTIVITY
Authors: BUCKLEY DOUGLAS I. , RAMACHANDRAN J.
Published: August 2010

α‐Metanotropin (α‐MSH) was iodinated and 3,5‐diiodotyr2 ‐α‐MSH was isolated by reverse phase high performance liquid chromatography (HPLC). Catalytic dehalogenation of the diiodo derivative in the presence of tritium resulted in the formation of 3,5‐ditritiotyr2 ‐α‐MSH. The tritiated peptide was purified by ion exchange and partition chromatography. The radioactive peptide was found to be homogeneous and identical to α‐MSH by paper electrophoresis and HPLC. The tritiated α‐MSH stimulated lipolysis in rabbit adipocytes nearly as well as α‐MSH. The specific radioactivity of tritiated α‐MSH was 42 Ci/mmol or 73% of the theoretical value.
SYNTHESIS OF HISTONE MODEL SEQUENCES FOR IMMOBILIZATION ON A CROSS‐LINKED POLYACRYLATE MATRIX
Authors: ECKSTEIN HEINER , BAYER ERNST
Published: August 2010

The synthesis of three peptide sequences which are useful as histone models, [Lys]5,† [Lys]5‐Pro and the sequence 17–27 of the lysine‐rich histone from rabbit thymus Pro‐Ala‐Lys‐Lys‐Lys‐Lys‐Ala‐Ala‐Lys‐Lys‐Pro is described. Three different methods for the synthesis are applied. [Lys]5 is synthesized from the amino end beginning with Nα‐acryloyl‐Ne‐Cbo‐lysine by successive coupling of Cbo‐lysine to yield the pentalysine monomer CH2=CH—CO—[Lys(Cbo)]5 which can be used directly for radical copolymerization. [Lys]5‐Pro is synthesized according to the conventional peptide synthesis using the carbobenzoxy group for Nα‐protection and the tert.‐butyl group for side chain protection. The carboxyl function is protected as tert.‐butyl ester. The undecapeptide is synthesized in a similar manner. Instead of purifying the intermediate peptides by extraction, chromatography is used exclusively. The isolation of the unprotected peptides Lys‐Pro, [Lys]3‐Pro, [Lys]4‐Pro, [Lys]5‐Pro and Pro‐Ala‐[Lys]4‐[Ala]2‐[Lys]2‐Pro and their characterization using amino acid analysis, electrophoreses and field desorption mass spectrometry is also reported.
SYNTHESIS OF TWO ANALOGS OF A CYCLIC HEXAPEPTIDE WITH DISULFIDE BRIDGE CORRESPONDING TO BOVINE PROTHROMBIN PRECURSOR SEQUENCE 18–23: Extent of Carboxylation by Vitamin K‐Dependent Carboxylase
Authors: RICH DANIEL H. , KAWAI MEGUMI , GOODMAN HEDDA L. , SUTTIE JOHN W.
Published: August 2010

The synthesis of two analogs of sequence 18–23 of bovine prothrombin precursor is described. Hexapeptides Boc‐Cys(Acm)‐Leu‐Glu(OBzl)‐Glu (OBzl)‐Pro‐Cys(Acm)‐OBzl and Ac‐Cys(Acm)‐Leu‐Glu(OBzl)‐Glu(OBzl)‐Pro‐Cys(Acm)‐OMe were synthesized in solution by stepwise addition of Boc‐amino acids using dicyclohexylcarbodiimide/N‐hydroxybenzotriazole as the coupling reagent. The acetamidomethyl groups were cleaved and oxidized, using iodine in methanol, to the protected cyclic disulfide in 62–69% yield. The 0‐benzyl groups were removed either by treatment with anhydrous hydrogen fluoride or hydrogen bromide in trifluoroacetic acid to give the cyclic hexapeptide disulfides, R1‐Cys‐Leu‐Glu‐Glu‐Pro‐Cys‐OR2 where R1, = H or Ac and R2 = H or CH3. The cyclic hexapeptides were evaluated as substrates for vitamin K‐dependent carboxylase. Both peptides are unusually poor substrates for the carboxylase, and each appears to inhibit carboxylation of Phe‐Leu‐Glu‐Glu‐Leu, a good substrate for the enzyme.
OCCURRENCE OF ASPARAGINE IN “DISALLOWED” CONFORMATIONS IN PROTEINS
Authors: RAVICHANDRAN V. , SUBRAMANIAN E.
Published: August 2010

A survey of 37 proteins has confirmed the frequent occurrence of asparagine in conformations having φ < 180°, a region of the Ramachandran plot generally disallowed for amino acids with side chains possessing Cβ atom and beyond. Model building studies suggest the possibility of an intramolecular hydrogen bond between the amino group of the asparagine side chain and the (backbone) carbonyl oxygen atom of the same residue.
STUDIES OF PEPTIDE ANTIBIOTICS:
Authors: KOSUI NOBUO , KATO TETSUO , IZUMIYA NOBUO
Published: August 2010

Tyrocidine A (TA) is an antibiotic cyclic decapeptide with the sequence of cyclo (‐L‐Val1 ‐L‐Orn2‐L‐Leu3‐D‐Phe4‐L‐Pro5‐L‐Phe6‐D‐Phe7‐L‐Asn8‐L‐Gln9‐L‐Tyr10‐). Gramicidin S (GS) regarded as a homolog of TA is also a cyclic decapeptide with the sequence of cyclo (‐L‐Val1‐L‐Orn2‐L‐Leu3‐D‐Phe4‐L‐Pro5‐ L‐Val6‐L‐Orn7‐L‐Leu8 ‐D‐Phe9 ‐L‐Pro10 ‐). GS shows higher antibacterial activity, whereas TA exhibits inhibitory activity on the biosynthesis of RNA. Two analogs of TA, [L‐Val6]‐TA (12a) and [L‐Orn7]‐TA (12b), were synthesized by the conventional method in order to study the interrelationships between the two related antibiotics TA and GS. Antibacterial activities of 12a and TA are nearly the same, but the activity of 12b is significantly lower. The optical rotatory dispersion spectra of 12a, 12b, and TA showed a trough at 233 nm region; the troughs of 12a and TA are nearly the same in depth, but the trough of 12b is shallower. Relationships between structure and activity of 12a and 12b compared with TA and GS were discussed.
COMPARISON OF THE STRUCTURAL FEATURES OF CORTICOTROPIN REQUIRED FOR STIMULATION OF STEROIDOGENESIS AND cAMP PRODUCTION IN RAT AND RABBIT ADRENOCORTICAL CELLS
Authors: RYBAK S.M. , RAMACHANDRAN J.
Published: August 2010

The steroidogenic activities of ACTH, α‐MSH, β‐MSH as well as analogs of the hormones have been compared in rat and rabbit adrenocortical cells. ACTH is equally active in both species and the melanotropins have very low steroidogenic potency in either species. The steroidogenic potencies of the peptide analogs are strikingly similar in the two species, suggesting that the structural requirements for eliciting steroidogenesis are the same in rat and rabbit adrenocortical cells. The analog NPS‐ACTH has low, comparable steroidogenic activity in both species. NPS‐ACTH is a potent antagonist of ACTH‐induced cAMP production in rat adrenocortical cells but acts as a weak partial agonist in rabbit adrenocortical cells. These results suggest that steroidogenesis may be mediated by receptors different from those involved in the cAMP response observed at supraphysiological concentrations of ACTH.
GAMMA‐MELANOTROPIN IS NOT PRESENT IN AN N‐TERMINAL PEPTIDE OF SALMON PROOPIOCORTIN
Authors: Kawauchi Hiroshi , Takahashi Akiyoshi , Abe Ken‐Ichi
Published: August 2010

The N‐terminal peptide of salmon proopiocortin has been isolated and the primary structure including two disulfide bonds elucidated. The peptide consisted of 76 amino acid residues, which is 27 residues shorter than the bovine and human peptides. The N‐terminal 44 residues of the teleost peptide exhibited significant sequence homology to those of the mammalian peptides. The salmon peptide, however, is lacking in the counterpart of gamma‐MSH which is located between residues 51 and 64 in the mammalian peptides.
CYCLIC ANALOGUE OF BRADYKININ POSSESSING SELECTIVE AND PROLONGED BIOLOGICAL ACTIVITY
Authors: Chipens G.I. , Mutulis F.K. , Katayev B.S. , Klusha V.E. , Misina Lp. , Myshlyiakova N.V.
Published: August 2010

Cyclo‐[(Nε1‐Lys1, Gly6)‐bradykinin] and its deprotected non‐cyclic precursor, PheGlyProPheArg‐LysProProGly, were synthesized using the conventional methods of peptide chemistry. Similar to bradykinin, the cyclopeptide elicits a depressor reaction in rats, as revealed by the experiments in vivo. Its duration of action, however, is greater by several orders of magnitude. At the same time, it appears to exhibit no myotropic activity when applied in vitro to extravasal smooth muscle preparations (uterus and ileum of the rat). The non‐cyclic precursor lacks the depressor activity, but produces a slight myotropic effect (α= 0.6 ± 0.09; pD2= 5.9 ± 0.17).
INTERACTION OF HUMAN SERUM ALBUMIN WITH HEMATOPORPHYRIN AND ITS ZN2+‐AND FE3+‐DERIVATIVES
Authors: Reddi Elena , Ricchelli Fernanda , Jori Giulio
Published: August 2010

Human serum albumin at pH values above 6.8 has one strong binding site for hematoporphyrin; the stability constant of the 1:1 complex is about 106 M‐1 as determined by Scatchard plot after estimation of the bound hematoporphyrin‐induced quenching of the fluorescence emitted by the single tryptophanyl residue of the protein. Determination of the tryptophan‐to‐hematoporphyrin energy transfer efficiency yields a Förster parameter R0 of 6.2–6.9nm, depending on the value chosen to represent the donor‐acceptor mutual orientation, and a tryptophan‐to‐hematoporphyrin distance of about 1.7nm. Zn2+‐ and Fe3+‐ hematoporphyrin also give a 1:1 complex with albumin, probably binding at the same site as hematoporphyrin, as shown by the identity of the energy transfer parameters; however, the metal ions do not appear to be involved in the formation of the albumin‐porphyrin complex. The albumin‐hematoporphyrin interaction is drastically affected by the pH of the medium; below pH 6.5 we find a large number of binding sites with weak affinity for hematoporphyrin, which disappear upon increasing the pH. The main site, below pH 6.5, has an affinity comparable with that of the secondary sites. Circular dichroism studies show that the pH effect is due to a change in the protein conformation leading to different interactions between bound porphyrin and specific amino acid side chains.
Theoretical conformational analysis of enkephalin analogues related to fluorescence and n.m.r. measurements in aqueous solution
Authors: Demonte Jean‐Paul , Guillard Roger , Englert Anne
Published: August 2010

The properties related to non‐radiative energy transfer of a number of enkephalin analogues with tryptophan substituted for phenylalanine in position 4 and n.m.r. 3JNH‐CαH coupling constants of corresponding [Phe4]‐enkephalin analogues are being derived from semi‐empirical conformational energy. The molecules considered contain a glycyl, a D‐alanyl or an L‐alanyl as second residue; two of the compounds are N‐methylated at position 4 or 5. The [Trp4]‐ enkephalin analogues and the corresponding [Phe4]‐enkephalin analogues display nearly parallel affinities in the opiate receptor binding assay (Schiller et al.(1)). The comparison of computed and experimental properties shows that an ensemble of conformers is a satisfactory representation of the state of these molecules in water.
Racemization of free and protein‐bound amino acids in strong mineral acid
Authors: Liardony Remy , Jost Rolf
Published: August 2010

A new GC/MS technique was applied to measure the racemization of amino acids in strong mineral acid. The inversion rate constants of 15 free amino acids were determined under standard hydrolysis conditions (110°, 6N HCl in evacuated vacuum‐sealed tubes). The variations in the inversion rate constants of all tested amino acids with the exception of serine and threonine were related to two factors: side‐chain electron‐withdrawing capacity (s̀*) and steric hindrance in the vicinity of the α‐hydrogen atom. The rate constants for serine and threonine were much lower than expected. Hydrolysis‐induced racemization of protein‐bound amino acids was investigated with α‐lactalbumin and β‐lactoglobulin. Significant differences were observed as compared with the racemization rates of free amino acids. Such discrepancies were also observed between the two proteins. In the early stage of α‐lactalbumin hydrolysis, 10% inversion of methionine was measured as compared with less than 0.5% in the case of β‐lactoglobulin. We attributed the particular behaviour of methionine in α‐lactalbumin to the neighbourhood of a cysteine residue on the carboxyl side.
CD and 1 H‐n.m.r. studies on the side‐chain conformation of tyrosine derivatives and tyrosine residues in di‐ and tripeptides
Authors: JUY MICHEL , LAM‐THANH HUNG , FERMANDJIAN SERGE
Published: August 2010

Tyrosine, tyrosine peptides and derivatives, in total 11 species, were selected as models for the study of optical properties (1Lb band of phenolic group) and side‐chain arrangement (rotamers around Cα – Cβ bond) of tyrosine as a function of chemical structure and pH effects. Circular dichroism spectra between 240 and 320 nm and n.m.r. spectra were recorded for the different ionization states. Results are discussed in terms of charge effects from N‐ and C‐terminal groups and local conformation influence on 1Lb band of the phenolic chromophore and on distribution of rotamer populations in side‐chain of tyrosine. Fractions of rotamer populations were estimated from α‐β proton‐proton coupling constants and, in the cases of tyrosine and N‐acetyl‐tyrosine, from 15N‐β nitrogen‐proton coupling constants, which allow the stereospecific assignment of the β and β′ protons. The rotamer populations of tyrosine, averaged from all the data of the samples in solution, were then compared with their statistical distribution in the solid state. Interestingly, agreement is excellent when we refer to crystal of tyrosine, tyrosine derivatives or small peptides (31 samples) and poor in the case of proteins. This leads to a discussion on both the validity of using statistical distributions of rotamers in proteins as reference for rotamer preferences inside small peptides in solution and the choice of the appropriate Jg and Jt values in Pachler's approach. The possible existence of a correlation between ellipticity and rotamer populations for such samples is examined.
Hydrogenolytic debenzylation of sulfur‐containing peptides
Authors: LOSSE G. , STIEHL H. U. , SCHWENZER B.
Published: August 2010

S‐protected cysteine derivatives are desulfurized by hydrogenation with Pd/H2 forming inhibiting thiols and alanine derivatives. In the case of protected cysteine peptides, this inhibition effect may be suppressed by adding BF3‐etherate, the extent of suppression depending on the position of the cysteine and on the sequence length of the peptide derivative. With sufficient sequence distance from the cysteine sulfur, benzyl type protecting groups may be quantitatively removed from the cysteine sulfur by means of hydrogenolysis.
Structural characterization of iodinated bovine growth hormone
Authors: MATTERA RAFAEL , TURYN DANIEL , FERNANDEZ HORACIO N. , DELLACHA JUAN M.
Published: August 2010

Bovine growth hormone (bGH) was submitted to iodination using limited amounts of oxidizing reagent, yielding a derivative with no more than 1 g‐atom of iodine per mole of hormone. Analysis of the hydrolysis products indicated that monoiodotyrosine was almost the only product of substitution. Isolation and identification of the tryptic fragments showed that half of the 125 I‐labeled bGH molecules were iodinated in Tyr 174, followed by Tyr 158 (16%) and Tyr 42 (14%). Frontal gel chromatography indicated that the preparation did not contain significant amounts of unreacted bGH. Circular dichroism evidenced structural similarity between the native and the iodinated bGH. The iodinated hormone, like the native protein, undergoes self‐association. The dissociation constant of the iodo‐labeled bGH self‐association equilibrium showed a twofold increase when compared to that corresponding to the unlabeled hormone. At pH 8.5, where the equilibrium constant was estimated, one tenth of the molecules bear a charged iodotyrosyl residue (average pKapp = 9.3), which could account for part, if not all, of the observed difference regarding self‐association. By this criterion, the presence of the iodine atom does not disturb the area engaged in dimer formation.
Biological and immunological characterization of iodinated bovine growth hormone
Authors: MATTERA RAFAEL , DELLACHA JUAN M.
Published: August 2010

Iodinated bovine growth hormone, containing no more than 1 g‐atom of iodine per mole of hormone is generally used as a tracer in studies related to the action and metabolism of the hormone. This derivative was tested in different biological and immunological systems in which the hormone is known to be active. The iodinated derivative was almost indistinguishable in its properties from the native hormone when it was examined by the following criteria: body growth promoting activity, rat liver uptakein vivo, binding to rabbit liver microsomes and primary antigen‐antibody interactions. Micro‐complement fixation experiments suggested that the iodination produces minor alterations in the affinity of some antigenic determinants.
Studies on prolactin
Authors: GRÁF LÁSZLÓ
Published: August 2010

Insoluble trypsin has been shown to attack preferentially some peptide bonds of ovine prolactin, within the large disulfide loop. The peptide bond most susceptible to immobilized trypsin was identified as the Arg125‐Leu126 of the ovine prolactin structure.
Synthesis of some biologically active substituted thiazole and thiazoline‐amino acid derivatives
Authors: EL‐NAGGAR A.M. , AHMED F.S.M. , EL‐SALAM A.M. ABD , HAROUN B.M. , LATIF M.S.A.
Published: August 2010

Synthesis of a series of N‐(2‐acetylaminothiazole‐5‐sulphonyl) amino acids (II–VI) and some of their corresponding methyl esters (VII–XI) is described. Coupling of N‐tosyl‐ or N‐phthalylamino acid with 2‐amino‐2‐thiazoline using the DCC method furnishes 2‐(N‐tosyl‐ or N‐phthalylamino acyl)amino‐2‐thiazolines (XII–XXI). Hydrazinolysis of 2‐(N‐Pht‐L‐Phe or N‐Pht‐L‐Ala)amino‐2‐thiazoline in ethanol afforded 2‐(L‐Phe or L‐Ala) amino‐2‐thiazoline (XXII and XXIII) respectively. Synthesis of the dipeptide 2‐(N‐Tos‐L‐Val‐L‐Leu) amino‐2‐thiazoline (XXIV) has been achieved employing the azide method. Sixteen thiazole‐ and thiazoline‐amino acid derivatives were found to be active against a number of microorganisms.
Steric effect exerted by the proline residue on the antecedent alanine residue
Authors: SIEMION I.Z. , SOBCZYK K. , NAWROCKA E.
Published: August 2010

Five model tetrapeptides: Ala‐Ala‐Ala‐Ala, Pro‐Ala‐Ala‐Ala, Ala‐Pro‐Ala‐Ala, Ala‐Ala‐Pro‐Ala and Ala‐Ala‐Ala‐Pro, were synthesized and measured in D2O by 13C‐n.m.r. spectroscopy. The spectra analysis led us to the conclusion that for each model (irrespective of pD) in conformational equilibrium, the predominant conformation is the one in which side methyl of alanine preceding proline residue eclipses alanine carbonyl group. The influence of pD changes on cis‐trans isomerism of Ala‐Pro amide bond was also investigated.
Synthesis and pharmacological activity of dermorphin and its N‐terminal sequences
Authors: SALVADORI SEVERO , SARTO GIANPIETRO , TOMATIS ROBERTO
Published: August 2010

H‐Tyr‐D‐Ala‐Phe‐Gly‐Tyr‐Pro‐Ser‐NH2 (demorphin), an opiate‐like peptide, and tri‐, tetra‐, penta‐ and hexapeptide‐amide analogs, were synthesized by conventional methods in solution, to determine the minimum peptide chain‐length, required for analgesic activity.
Specificity of pepsin‐catalyzed peptide bond synthesis
Authors: BOZLER HERMANN , WAYNE SUSAN I. , FRUTON JOSEPH S.
Published: August 2010

The rates of the pepsin‐catalyzed synthesis of oligopeptides of the general type A‐Phe‐Leu‐B by the condensation of A‐Phe‐OH with H‐Leu‐B have been determined by means of analytical high performance liquid chromatography. Variation of the A group led to large changes in the initial rates of the condensation reaction, and the effect of such changes was found to be similar to that previously found for the secondary specificity of pepsin in the hydrolysis of oligopeptide substrates. Replacement of the Phe and Leu residues of A‐Phe‐OH or H‐Leu‐B by other amino acid residues gave relative rates of synthesis in accord with the known primary specificity of the hydrolytic action of pepsin. Partially‐acetylated pepsin, which exhibits enhanced hydrolytic activity, also catalyzed the condensation reaction more effectively. The results are discussed in relation to the potential utility and limitations of pepsin as a catalyst in the preparative synthesis of oligopeptides and to the problem of the mechanism of its action.
The rate of s‐cis/s‐transisomerization in angiotensin II is at least 70‐fold greater than in His‐Pro and is not rate limiting in receptor binding
Authors: GALARDY RICHARD E. , LIAKOPOULOU‐KYRIAKIDES MARIA
Published: August 2010

The dipeptide L‐histidyl‐L‐proline interconverts between the s‐cisand s‐transrotational isomers of the amide bond with an average rate constant of 2.0 ks‐1at 22.5°. This rate is independent of pH throughout the pH range 5.5–8.5 as determined by pH jump from low pH with potentiometric recording of the slow approach to equilibrium pH, and by integration of the histidine C‐2 and C‐4 proton n.m.r. resonances as a function of time following pD jump from low pD. From the temperature dependence of the n.m.r. experiments this inter‐conversion has an Arrhenius activation energy of 20 kcal mol‐1and a free energy of activation of 21 kcal · mol‐1, similar to other simple acyl‐ and aminoacylprolines. The octapeptide angiotensin II containing L‐histidyl‐L‐proline at position 6–7 interconverts at least 70‐fold faster than the free dipeptide. This rate is too fast to be rate limiting in the binding of angiotensin II to its receptor in rat adrenal cortex.
Physicochemical characteristics of homogeneous bovine lung angiotensin I‐converting enzyme
Authors: HARRIS ROBERT B. , WILSON IRWIN B.
Published: August 2010

Angiotensin I‐converting enzyme was purified to electrophoretic homogeneity (12 units/mg) from bovine lung tissue and from human serum using an affinity gel described previously (Harris et al., (1981) Anal. Biochem. 111, 227–234). The isoelectric point (4.5), molecular weight (145 000), S20, w(8.1), amino acid composition and carbohydrate content of the lung enzyme are all similar to the values obtained for the human serum enzyme. The NH2 ‐terminus of the lung enzyme (Ala) is different from that of the serum enzyme (Tyr) but the COOH‐ terminal sequences are identical (‐Leu‐Ser‐OH). Pure bovine lung enzyme was reduced and carboxyamidomethylated with iodo (14C1) acetamide to the extent predicted by the number of cysteine residues. Since no radioactivity was incorporated into denatured enzyme that was not reduced, all of the cysteine residues must be in the form of disulfide bonds. Reverse‐phase HPLC was used to separate peptides obtained from the lung enzyme after degradation with either trypsin or cyanogen bromide. The number of peptides resolved (42 after trypsin, 31 after cyanogen bromide), were only 20% fewer than the number predicted from the amino acid analysis and therefore the possibility that the converting enzyme (a single polypeptide chain) might be a fused dimer is excluded.
Cyclic peptides
Authors: KANMERA TATSUHIKO , IZUMIYA NOBUO
Published: August 2010

A cyclic tetradepsipeptide with a sequence corresponding to AM‐toxin III (a phytotoxic peptide) was synthesized by a conventional method in order to confirm the proposed structure. This was mediated through a deamination reaction of precursor cyclotetradepsipeptide containing a d‐2, 3‐diaminopropionic acid residue by the Hofmann degradation method. The synthetic peptide and natural AM‐toxin III were identical in regard to t.l.c., crystal form, mass spectrum and biological activity in causing necrosis on apple leaves. Two analogs, [1‐O‐methyl‐l‐tyrosine]‐AM‐toxin and [1‐l‐tyrosine]‐AM‐toxin, were synthesized simultaneously. [1‐l‐Tyrosine]‐AM‐toxin showed extremely weak activity; the relationship between the bulkiness of an aromatic side chain at position 1 of AM‐toxin III and its biological activity is discussed.
β‐Endorphin
Authors: YAMASHIRO DONALD , HAMMONDS R. GLENN , LI CHOH HAO
Published: August 2010

Ostrich β‐endorphin has been synthesized by the solid‐phase method. Opiate activity in a radioreceptor binding assay is about seven times that of human β‐endorphin. Structural differences within positions 6–15 account for the increased binding potency.
β‐Endorphin
Authors: HAMMONDS R. GLENN , LI CHOH HAO
Published: August 2010

The potency of a series of synthetic analogs of β‐endorphin in inhibiting binding of [3H2‐Tyr27]‐βh‐endorphin to either rat brain membranes or neuroblastoma x glioma hybrid cells (NG108–15) has been determined and compared with the previously determined analgesic potency. There is a very good correlation between inhibitory potency in membranes and cells, but the correlation between analgesic potency and inhibitory potency in either membranes or cells is not as good.
β‐Endorphin
Authors: FERRARA PASCUAL , LI CHOH HAO
Published: August 2010

Human β‐endorphin analogs with various chain lengths have been investigated for their potency in displacing tritiated dihydromorphine and Leu‐enkephalin binding in rat brain membrane preparations. It was found that the reduction of chain length from residues 1–31 to 1–5 led to a gradual loss of preference for the morphined receptor. In addition, the extension of the chain length of the Metekephalin segment to theCOOH‐terminal glutamic acid modified the binding of theNH2‐terminal sequence to the enkephalin receptor. The fact that camel β‐endorphin is more potent in displacing the two tritiated primary ligands than the human hormone is also reported herein.
A functioning complex of two cytochrome c fragments with deletion of the (39–58) eicosapeptide*
Authors: WESTERHUIS L.W. , TESSER G.I. , NIVARD R.J.F.
Published: August 2010

Two major fragments of horse heart cytochrome c involving the sequences (1–38) and (60–104) were found to produce a stable complex. The two fragments were devoid of any cytochrome c activity. The complex exhibited a hardly measurable electron transfer capacity with respect to cytochrome c oxidase and missed the 695 nm absorption band. The introduction of tryptophan in position 59 restored the intrinsic activity of the complex to the level of native cytochrome c. This was concluded from the convergence of the Eady‐Hofstee plots which extrapolate to the same Vmax at high substrate concentrations. The absorption spectrum of the complex in the ferriform contained a clear absorption band at 695 nm (84% of that found with native cytochrome c).

The investigation proves the indispensability of tryptophan in position 59 for the transfer of an electron to cytochrome c oxidase and supports the conclusions of Parr et al. about the existence of two consecutive processes in the folding of the two fragments (vide infra).
Statistical molecular model for hydrated peptides
Authors: Demonte Jean‐Paul
Published: August 2010

A statistical molecular model for hydrated peptides is used to simulate the behaviour of various peptide chains in aqueous solution. The reliability of the model is ascertained by the evolution of the characteristic ratio, Cn, for hydrophobic and hydrophilic polypeptide chains, such as, respectively, poly‐Ala and poly‐Ser. The comparison of computed and experimental properties related to non radiative energy transfer of angiotensin II analogs, assuming that an ensemble of conformers is a satisfactory representation of the state of these molecules in water, provides further support for the model.
β‐Endorphin: synthesis and properties of human β‐endorphin‐(1–28) and its analogs
Authors: Garzia Raffaella , Yamashiro Donald , Li Choh Hao , Nicolas Pierre
Published: August 2010

Three analogs of human β‐endorphin (βh‐EP) were synthesized by the solid‐phase method: βh‐EP‐(1–28) (II), [D‐Ala2, Gln8] ‐ βh‐EP‐(1–28) (III). Radioreceptor binding assay with use of tritiated βh‐EP as primary ligand gave relative potencies as follows: βh‐EP, 100; I, 85; II, 380; III, 146. Relative potencies in an analgesic assay were: βh‐EP; 100; I, 18; II, 36; III, 13.
Unusual intramolecular hydrogen bonding in cycloamanide A, cyclic (LPro‐LVal‐LPhe‐LPhe‐LAla‐Gly)
Authors: CHIANG CHIAN CHIAN , KARLE ISABELLA L. , WIELAND TH.
Published: August 2010

The naturally occurring cyclic hexapeptide, cycloamanide A, has only one intramolecular hydrogen bond. It is a 4 ← 1 type that encompasses the LPhe‐LAla sequence in which the experimentally determined ø, ← values are + 54d̀, – 118d̀ and – 88d̀, – 4d̀, respectively. Even though the chirality is L, L, the ø, ← values are characteristic for a D, L β‐bend, Type II°. The conformation of the molecule was established by a crystal structure determination using X‐ray diffraction analysis. Cycloamanide A (C33H42N6O6←. 4H2O) crystallizes in space group P212121 with cell parameters a = 13.307(2) Å, b = 24.820(4) Å and c = 11.231(1) Å.