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W Göhring

Publications and source records attributed to W Göhring.

At least 55 records · Page 3Linked to original sources
PubMed1989

Conformational and biological properties of the Ala10 analogue of human des-Trp1,Nle12-minigastrin.

Synthesis, conformation, and biological properties of the Ala10 analogue of des-Trp1,Nle12-minigastrin are reported. Replacement of the Gly residue in the original sequence with Ala remarkably changes the conformational preference of the hormone in trifluoroethanol. CD and NMR results indicate that the conformational change is mainly located in the C-terminal portion of the molecule, with probable extension of the N-terminal alpha-helix throughout the entire sequence. The structural modification causes a 10-fold decrease in the biological potency of the hormone, which is about as active as the C-terminal tetrapeptide amide. These findings support our previous hypothesis that the optimal bioactive conformation of the native hormone is U-shaped, with mutual interactions among the two end segments.

Alanine↗
PubMed1989

Muramyl-peptide/gastrin conjugates as potential immunogens.

For a selective covalent linkage of muramyl-peptides with human-little-gastrin the maleimide-thiol reaction principle was adopted. For this purpose thiol-functionalized muramyl-peptide derivatives, i.e. N-acetyl-muramyl-alanyl-D-isoglutaminyl-cysteamine and N-acetyl-muramyl-alanyl-D-isoglutaminyl-N epsilon-palmitoyl-lysyl-cysteamine, were reacted with N alpha-maleoyl-beta-alanyl-[15-methoxinine]-human-little-g ast rin-I-[2-17]. The resulting gastrin conjugates were used in immunization experiments on rabbits and mice. Unexpectedly, these gastrin derivatives proved to be poorly immunogenic despite the built-in immunoadjuvanticity. The titers of the antipeptide antibodies as well as of the unspecific immunoglobulins were in the range of those of the control group.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1988

Synthesis of the bis-cystinyl-fragment 225-232/225'-232' of the human IgGl hinge region.

In human IgGl the two heavy chains are crosslinked in the central portion of the molecule by two disulfide bridges forming a double chain bis-cystinyl cyclic peptide in parallel alignment. For our synthetic studies we have chosen the sequence portion 225-232/225'-232', i.e. [H-Thr-C1ys-Pro-Pro-C1ys-Pro-Ala-Pro-OH]2. By the use of a combination of the S-tert.-butylthio and the S-acetamidomethyl groups selective cysteine pairings in two successive steps produced the hinge hexadecapeptide in parallel and antiparallel alignment as homogeneous and well characterized compounds. Thiol disulfide interchange experiments on the antiparallel dimer led to over 90% conversion to the parallel isomer. Similarly random air-oxidation was found to generate again mainly the parallel dimer, thus strongly suggesting that this sequence portion contains sufficient structural information for a correct assembly of the two heavy chains of immunoglobulins without decisive contribution of a protein disulfide isomerase.

Amino Acid Sequence↗
PubMed1987

Synthesis of human [15-norleucine]little-gastrin-II and des-1-tryptophan-[12-norleucine]minigastrin-II.

By the use of a newly developed procedure for the synthesis of tyrosine-O-sulfate peptides based on the direct incorporation of the suitably N alpha-protected tyrosine-O-sulfate residue along the synthetic route, the synthesis of two human gastrin-II analogues was successfully accomplished. Thereby acid labile side chain protection was applied in combination with the N alpha-benzyloxycarbonyl group in the intermediate chain elongation steps. Despite the pronounced acid-lability of the sulfate ester moiety, its hydrolysis during the final acidolytic deprotection step was significantly reduced under optimized conditions. Subsequent chromatographic purification led to the two gastrin analogues in satisfactory yields as highly pure compounds as judged by various indicative analytical assays.

Amino Acid Sequence↗
PubMed1987

Studies on immunoassays of peptide factors. II. Fluorescence enzyme immunoassay for human little-gastrin.

The fluorogenic chymotrypsin substrate N alpha-(4-carboxybutyryl)-L-phenylalanine (4-methyl-7-coumaryl)amide was converted to a thiol-containing compound via its condensation at the carboxyl function with cystamine followed by reduction of the resulting disulfide compound to a cysteamine derivative. By subsequent reaction of the thiol group with N alpha-maleoyl-beta-alanyl-human-little-gastrin-I-[2-17] a fluorogenic substrate-labeled gastrin, fully immunoreactive against antigastrin antisera, was obtained. This tracer was then applied for developing a fluorescence immunoassay based on separation of bound and free tracer followed by chymotryptic digestion of the fluorogenic substrate in the supernatant. The fluorescence intensity of the extracted fluorophore i.e., 7-amino-4-methyl-coumarin, was found to monitor gastrin concentrations in a reproducible manner. With the model peptide hormone human little-gastrin-I the sensitivity of this alternative immunoassay procedure was well documented.

Amino Acids↗
PubMed1987

Studies on immunoassays of peptide factors. III. Gastrin/iso-1-cytochrome C as immunogen for raising anti-gastrin antisera.

Iso-1-cytochrome c contains in penultimate position of its sequence a cysteine residue which in analogy to the known tertiary structures of cytochromes c should be exposed on the surface of the protein. Its selective reaction with N alpha-maleoyl-beta-alanyl-human-little-gastrin-I-[2-17] led to a well characterized and homogeneous gastrin conjugate to be used as immunogen in rabbits. The antisera raised by this procedure exhibited a degree of specificity for the hormone gastrin parallel to that of the gastrin receptor. This is clearly documented by comparison of the immune crossreactivities of gastrin-peptides of increasing chain length and of fragments corresponding to various regions of the hormone molecule with their biological activity. The immune response provoked in the animals by the use of an homogeneous immunogen was found to be highly reproducible in terms of specificity of the antigastrin antibodies.

Binding, Competitive↗
PubMed1987

Studies on immunoassays of peptide factors. V. Synthesis of cholecystokinin-58-[1-11]/iso-1-cytochrome c conjugate.

In previous studies on model compounds we have found that the maleimide function is sufficiently stable under the conditions of peptide synthesis to allow its incorporation at preselected positions of a peptide chain in earlier steps of the synthetic route. Taking advantage of this observation the N-terminal undecapeptide of canine cholecystokinin-58 containing at its N-terminus the maleimide group became accessible in high yields as chromatographically homogenous and analytically well characterized compound. Via the incorporated anchor group the undecapeptide was linked selectively at its N-terminus to the cysteine residue 107 of iso-1-cytochrome c to yield a well characterized conjugate of 1:1 stoichiometry for immunization experiments.

Cholecystokinin↗
PubMed1987

Studies on immunoassays of peptide factors. IV. New synthesis of a gastrin/peroxidase conjugate.

We have shown that structurally well-defined homogeneous maleoyl-peptides are synthetically accessible. These anchor-modified peptide derivatives allow their selective covalent linkage to thiol-containing proteins via the maleimide-thiol procedure. Correspondingly mercaptosuccinylated horseradish peroxidase was reacted with N alpha-maleoyl-beta-alanyl-human-little gastrin-I-[2-17] to produce the gastrin/peroxidase conjugate in good yields at 1:1 stoichiometry. The conjugate exhibited full enzymatic activity and identical binding affinity to antigastrin antisera as the parent gastrin. This approach proved to be well suited for the preparation of enzyme labeled peptide factors as tracers for immunoassays.

Enzyme-Linked Immunosorbent Assay↗
PubMed1986

Synthesis of human des-tryptophan-1,norleucine-12-minigastrin-II and its biological activities.

A human minigastrin-II analog was prepared by conventional methods in solution using N-benzyloxycarbonyltyrosine O-sulfate as starting material in the synthetic route. Upon removal of the acid-labile protecting groups and purification by preparative reversed-phase chromatography the sulfated gastrin peptide was obtained in satisfactory overall yields as homogeneous material. It was found to be about twice as active as the non-sulfated form in stimulating gastric acid secretion and to exhibit a 10-fold higher affinity to gastrin receptors of purified parietal cells.

Animals↗
PubMed1984

[Synthesis of peptides with gastrinlike activity. Studies on the structure-activity relationship of the natural hormone human little gastrin I].

To identify the role of the block of glutamic acid residues characteristic for the gastrin molecule, a series of shortened peptides related to the human little-gastrin-I sequence were synthesized. The biological activities of these gastrin peptides strongly suggest in the pentaglutamic acid sequence a specific information for a pronounced amplification of the hormonal activity.

Amino Acid Sequence↗
PubMed1983

Synthesis of the porcine intestinal peptide PHI and its 24-glutamine analogue.

PHI--a new candidate hormone from porcine intestinal tract-- corresponds to a linear heptacosapeptide amide of remarkable sequence homology to the known members of the glucagon family, particularly to the vasoactive intestinal peptide (VIP) and secretin. The position 24 usually occupied by an aminodicarboxylic acid omega-amide, in the present case, however, carries a glutamic acid, thus opening the question of whether this structural feature is related to desamidation in one of the isolation and characterization steps or of whether it is significant for this peptide factor. Consequently the heptacosapeptide amides corresponding to the proposed primary structure and to its 24-glutamine analogue have been synthesized. Comparative chromatographic and biological studies on the natural and the two synthetic products have confirmed the correctness of the primary structure proposed for the isolated PHI. Since [24-glutamic acid] and [24-glutamine]PHI exhibit no significant differences in their biological potencies, the main question is still open of whether the position 24 in native PHI is occupied by the aminodicarboxylic acid omega-amide (glutamine) or by N-substituted derivatives (N-glycosyl).

Amino Acid Sequence↗
PubMed1983

[Syntheses of human little gastrin-I and its leucine-15, norleucine-15 and methoxinine-15 analogs].

Human little gastrin-I is known to exhibit a high tendency to air-oxidation of its methionine-15 residue to the corresponding S-oxide derivative, with concomitant loss of biological activity. Since its leucine-15 analog, even if fully biologically active, differs significantly from the parent hormone in the immunological properties, the norleucine-15 and methoxinine-15 analogues were synthetized. For the required comparative analyses new syntheses of human little gastrin-I and of its leucine-15 analog were additionally elaborated. Upon an optimized condensation of the fragments, followed by the deprotection step, partition chromatography as well as preparative high-performance liquid chromatography led to the desired gastrins in satisfactory yields and high degree of purity as judged by the expected and known side products.

Amino Acid Sequence↗
PubMed1981

[Total synthesis of somatostatin-28 (author's transl)].

The total synthesis of the octacosapeptide corresponding to the proposed primary structure of porcine somatostatin-28 is described. The synthesis has been performed using a protection scheme of maximum selectivity (acid labile side chain protection based on tert-butyl alcohol and 1-adamantol derived protecting groups in combination with the S-tert-butylthio group for reversible and selective blocking of the cysteine thiol functions and the 2-nitrophenylthio group for the temporary protection of the alpha-amino functions of intermediate segments) and of carefully selected fragments. Upon assembly in sequence order of the four suitably protected fragments related to sequences 18-28, 15-17, 8-14 and 1-7, the asymmetric disulfides were reduced by exposure of the fully protected octacosapeptide to phosphines. Subsequently, the final deprotection was performed with trifluoroacetic acid and the resulting dihydrosomatostatin-28 was then converted by air oxidation into the "cyclic peptide". Gel filtration on Biogel P-6 and ion-exchange chromatography on Biogel CM-2 produced somatostatin-28 at a high degree of purity. Comparative analysis of the synthetic and natural product by means of chromatographic, immunological and biological assays confirmed the structure proposed for this putative precursor of somatostatin-14.

Amino Acid Sequence↗
PubMed1981

[Total synthesis of human big gastrin I. Revised primary structure (author's transl)].

The synthesis of the tetratriacontapeptide amide corresponding to the revised structure of human big gastrin I is described. The fully protected peptide derivative was obtained by assembly in sequence order of the suitably protected fragments [1--9], [10--14] and [15--34] via the dicyclohexylcarbodiimide/N-hydroxysuccinimide and azide method, respectively. Upon removal of the protecting groups by exposure to trifluoroacetic acid and purification of the resulting crude product by chromatographic methods, human big gastrin I was obtained in satisfactory yields and at a high degree of purity. The identical immunological crossreactivities of natural and synthetic human big gastrin I using anti-porcine big gastrin I antiserum strongly supports the correctness of the newly proposed primary structure of this member of the gastrin family.

Amino Acid Sequence↗
PubMed1981

[Studies on the total synthesis of cholecystokinin-pancreozymin. Synthesis of the suitably protected fragment corresponding to the sequence 24--33 (author's transl)].

The synthesis is described of a suitably protected decapeptide derivative corresponding to the C-terminal tyrosin-O-sulfate-containing sequence 24--33 of cholecystokinin-pancreozymin as key fragment for the total synthesis of this gastrointestinal hormone or its 39-variant. This peptide derivative has been prepared according to our newly developed procedure based on the direct use of N-acyltyrosine-O-sulfate barium salt. Additionally, removal of the protecting groups followed by purification via chromatographic methods produced the decapeptide amide in good yields and with a high degree of purity as a fully active cholecystokinin-pancreozymin related peptide.

Cholecystokinin↗
PubMed1981

[Cholecystokinin-pancreozymin synthesis. Synthesis of [28-threonine,31-norleucine]- and [28-threonine,31-leucine]cholecystokinin-pancreozymin-(25-33)-nonapeptide].

The syntheses of two analogues related to the C-terminal nonapeptide amide sequence 25-33 of cholecystokinin-pankreozymin are described. Based on the primary structure of the CCK-PZ-active caerulein and the experiences gained from the methionine replacement with leucine or norleucine in human little gastrin I, the analogues were designed by substituting methionine 28 with threonine, and methionine 31 with leucine and norleucine, respectively. Using a new method for the synthesis of tyrosine-O-sulfate-containing peptides, developed in our laboratory, and applying acid-labile side-chain protection in combination with the benzyloxycarbonyl group, the fully protected nonapeptide amide derivatives Z-Arg(Z2)-Asp(OBut)-Tyr-(SO3Ba1/2)-Thr(But)-Gly-Trp-Leu-Asp(OBut)-Phe-NH2 and Z-Arg(Z2)-Asp(OBut)-Tyr(SO3-Ba1/2)-Thr(But)-Gly-Trp-Nle-Asp(OBut)-Phe-NH2, were obtained. Upon hydrogenolytic and subsequent acidolytic removal of the protecting groups, followed by purification via chromatographic procedures the nonapeptide amides were isolated in satisfactory yields at a high degree of purity. In vivo and in vitro assays showed that a substitution of methionine 31 by norleucine with concomitant replacement of methionine 28 by threonine produced a fully active analogue, whereas for the threonine 28, leucine 31 analogue the pankreozymin-activity was lowered by a factor 10.

Amino Acid Sequence↗