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Y Shimohigashi

Publications and source records attributed to Y Shimohigashi.

124 records · Page 7Linked to original sources
PubMed1982

Dehydro-enkephalins. VI. Dehydroalanine3-enkephalin: a potent enkephalin analog for the delta opiate receptor.

The Gly3 residue in Gly2- and D-Ala2-enkephalins has been replaced by delta Ala3 and Ser3 in order to examine the effect on binding to the delta and mu opiate receptors. [D-Ala2, delta Ala3, Leu5]-enkephalin maintains most of its receptor binding affinities for both sites. It is suggested that the proper conjunctions of positions 2 and 3 of the enkephalin sequence are important to receptor preference and that position 3 may have a very specific interaction with the delta receptor. The in vivo analgesic and CNS activities of the peptides are also discussed.

Analgesia↗
PubMed1981

Cyclic peptides. XI. Synthesis of AM-toxin analogs by intramolecular condensation of pyruvyl-tripeptide amides.

In order to establish possible routes for the synthesis of AM-toxins, cyclotetradepsipeptides containing Dha, Pyr-L-Ala-L-Hmb-L-Tyr-NH2 were prepared and treated with TFA or anhydrous HF. The product was identified to be cyclo (-alpha-Hyala-L-Ala-L-Hmb-L-Tyr-), resulting from intramolecular condensation of the alpha-keto and amide group with the formation of the alpha-Hyala residue. Cyclo (-alpha-Hyala-L-Ala-L-Hmb-L-Phe-) and cyclo (-alpha-Hyala-L-Ala-L-Val-L-Phe-) were obtained by acid-treatment of the corresponding pyruvyl-tripeptide amides. The cyclic tetrapeptides did not show the activity of AM-toxin.

Amides↗
PubMed1978

Cyclic peptides. V. Synthesis of AM-toxin II and its analog.

A cyclic tetradepsipeptide with a sequence corresponding to AM-toxin II (a phytotoxic peptide) was synthesized in order to confirm the proposed structure by a conventional method. This was mediated through a dehydration reaction of cyclodepsipeptide containing a D-Ser residue, by methanesulfonyl chloride containing sulfur dioxide. The synthetic peptide and natural AM-toxin II were identical as regards t.l.c., crystal form, several kinds of spectra measurements and biological activity in causing necrosis on apple leaves. An analog, [L-Phe1]-AM-toxin, containing the lower homolog (L-phenylalanine) instead of L-2-amino-5-phenylpentanoic acid in position 1 of natural toxin II, was synthesized simultaneously. [L-Phe1]-AM-toxin showed extremely weak activity; the relationship between the bulkiness of an aromatic side chain and the biological activity of AM-toxin II is discussed.

Amino Acid Sequence↗
PubMed1977

Cyclic peptides. II. Synthesis of AM-Toxin I.

To confirm the structure of AM-toxin I (a phytotoxic cyclotetradepsipeptide) the proposed peptide was prepared by a conventional method. The synthetic peptide and natural AM-toxin I were identical as regards t.l.c., u.v., mass spectra and biological activity in causing necrosis on apple leaves. A prepared dimer of AM-toxin I showed extremely weak activity; the relationship between the ring size and biological activity of AM-toxin I is discussed.

Mass Spectrometry↗
PubMed1977

Cylic peptides. I. Synthesis of AM-toxin analog containing O-methyl-l-tyrosine.

An AM-toxin analog, cyclotetradepsipeptide, containing an O-methyl-L-tyrosine residue in place of an L-2-amino-5-arylpentanoic acid residue in AM-toxins has been prepared by a conventional method. The synthesis was attempted through six different routes and the desired analog was obtained by one such procedure. This compound showed extremely weak activity in causing necrosis on apple leaves.

Amino Acid Sequence↗
PubMedDate not supplied

Roles of lysine-69 in dimerization and activity of Trimeresurus flavoviridis venom aspartate-49-phospholipase A2.

Trimeresurus flavoviridis (Habu snake) venom aspartate-49-phospholipase A2 (Asp-49-PLA2) was reacted at pH 9.0 with a 2-fold molar excess of 2,4,6-trinitrobenzenesulfonate in the absence of Ca2+ and two trinitrophenylated derivatives were isolated by HPLC. One was a derivative modified at Lys-11 and its activity was mostly retained. The other was a derivative modified at both Lys-11 and Lys-72 and its activity was 40% that of unmodified enzyme. Trinitrophenylation of Lys-72 appeared to bring about a conformational disorder at the lipid-water interface recognition site and thus a reduction of activity. When the enzyme was modified in the presence of Ca2+, activity decreased at a rate much faster than that in the absence of Ca2+ and Lys-69 came to be modified. These results suggested that conformational displacement of Asp-49-PLA2 of a local to global type occurs upon the binding of Ca2+. The derivative modified at Lys-69 had 28% activity and existed as a monomer. This supports a previous assumption that Lys-69 participates in dimerization of group II Asp-49-PLA2s [Brunie et al. (1985) J. Biol. Chem. 260, 9742-9749] and shows that dimerization is not necessarily essential for activity manifestation.

Amino Acid Sequence↗
PubMedDate not supplied

Discriminatory recognition of membrane phospholipids by lysine-49-phospholipases A2 from Trimeresurus flavoviridis venom.

Basic proteins I and II (BP-I and BP-II) isolated from Trimeresurus flavoviridis venom, which are classified into a group of lysine-49-phospholipases A2 (Lys-49-PLA2), exhibited only limited lipolytic activity for the mixed micelles of various phospholipids. Based on the finding that BP-II elicits a strong contraction of guinea pig ileum due to the release of arachidonic acid, BP-II together with BP-I has been tested for their interaction with artificial phospholipid bilayer membranes. The dye leakage experiments indicated that BP-II interacts strongly with liposomes of beta-arachidonoyl-gamma-stearoyl-L-alpha-phosphatidylcholine. The perturbation of liposomes was observed only in the Ca(2+)-containing buffer, and as demonstrated by HPLC analyses, accompanied by the release of arachidonic acid. The concentration of Ca2+ which gave a half maximal activity of BP-II was 3.0 x 10(-4) M, suggesting that the affinity of BP-II for Ca2+ is more than 10 times stronger than that of BP-II without liposomes. These observations clearly show that Lys-49-PLA2 of BP-II is the enzyme responsible for the hydrolysis of membrane phospholipids and that Ca2+ is essential for such enzymatic activity. The interaction of BP-I with liposomes was much weaker than BP-II BP-I and BP-II share a common sequence except for Asp-67 (BP-I) and Asn-67 (BP-II) in the aligned sequences. This implies that the amino acid at position 67 of Lys-49-PLA2s is the residue required for discriminatory recognition of phospholipid membranes.

Animals↗
PubMedDate not supplied

Effect of modification of enkephalin C-terminal functions on affinity selection of opioid receptors.

Enkephalin analogs with various C-terminal modifications have been synthesized to evaluate the corresponding structural elements in the opioid receptors. The carboxyl group of the C-terminal leucine5 or glycine5 was converted into the mercaptomethyl (-CH2SH) and hydroxymethyl (-CH2OH) groups, starting from leucinthiol or leucinol for Leu5-derivatives and from cysteamine or ethanolamine for Gly5-derivatives. Interactions of synthetic peptides with the opioid receptors were examined by the radioligand receptor binding assays using rat brain and tritiated enkephalin analogs. The data suggest that the C-terminal carboxyl group in enkephalins is important, but not electrostatically, for interaction with delta-opioid receptors. With leucinthiol-enkephalin in biological assays which examine its inhibitory activity for electrically stimulated contractions of isolated smooth muscle, it was found that the reactive thiol group exists in the mu receptors present in the guinea pig ileum. Leucinthiol-enkephalin became bound covalently to this receptor-thiol group via disulfide formation after prolonged incubation.

Affinity Labels↗
PubMedDate not supplied

Trimeresurus flavoviridis venom gland phospholipase A2 isozymes genes have evolved via accelerated substitutions.

As a step towards understanding the structure and function of phospholipases A2 (PLA2s), five cDNAs encoding Trimeresurus flavoviridis venom gland PLA2 isozymes have been sequenced. They revealed that the 5' and 3' untranslated regions are much more homologous than the protein-coding regions and that base substitutions have occurred at similar rates for the three positions of codons in the protein-coding regions. Such novel findings are of great interest from the viewpoint of molecular evolution. To gain a further insight into this evolutional phenomenon, we have isolated and sequenced six T. flavoviridis PLA2 isozyme genes. Each gene consisted of four exons and three introns and encoded protein of 138 amino-acid residues, including the signal sequence of 16 amino-acid residues. The introns were much more homologous than the protein-coding regions of exons except for the signal peptide-coding region of the first exon. The absence of apparent functional role in the introns suggested that the protein-coding regions, except for the signal peptide-coding domains, have evolved at greater substitution rates than introns. The fact that the numbers of nucleotide substitutions per non-synonymous site are close to or larger than the numbers of nucleotide substitutions per synonymous site for relevant pairs of genes revealed that Darwinian-type accelerated substitutions have occurred in the protein-coding regions of exons. This is compatible with the presence of PLA2 species with diverse physiological activities in the venom.

Amino Acid Sequence↗
PubMedDate not supplied

The enzyme stability of dehydro-enkephalins.

Dehydro-enkephalins [delta Ala2]-, [delta Ala3]-, [delta Phe4]-, and [delta Leu5]enkephalins, were examined for their stability to enzymatic hydrolysis by carboxypeptidase Y [EC 3.4.16.1]. The successively liberated amino acids were determined quantitatively by amino acid analyses. The saturated leucine-enkephalin was rapidly hydrolyzed from the COOH-terminus. However, peptide linkages with alpha, beta-dehydroamino acid residues placed in the enkephalin molecule were strongly resistant to the enzyme at the carboxyl side and completely resistant at the amino side of the dehydro residue.

Amino Acids↗
PubMedDate not supplied

Predominant involvement of mu-rather than delta- or kappa-opiate receptors in LH secretion.

Opiate alkaloids and opioid peptides have been shown to suppress plasma LH and FSH levels via a naloxone sensitive mechanism in several species including man. Three subtypes of opiate receptors have been characterized: mu, delta and kappa. The present study was designed to investigate their role in gonadotropin release. Three highly selective opioid ligands, DAGO, MRZ and DTE12 (a dimeric tetrapeptide enkephalin), were injected intraventricularly into chronically ovariectomized rats. Injection of the mu-agonist at doses of 1 and 10 nmol produced a significant suppression of LH secretion, while the delta- and kappa-agonists had no significant effect. Thus, the mu-receptor seems to be the primary opiate receptor involved in the regulation of LH secretion. None of the opiate agonists employed had an effect on FSH secretion.

Animals↗
PubMedDate not supplied

Accelerated evolution of snake venom phospholipase A2 isozymes for acquisition of diverse physiological functions.

The nucleotide sequences of two cDNAs and four genes encoding Trimeresurus gramineus venom gland phospholipase A2 (PLA2) isozymes were determined and compared internally and externally with those encoding Trimeresurus flavoviridis venom gland PLA2 isozymes. It was revealed that the protein-coding regions are much more diversified than the 5' and 3' untranslated regions (UTRs) and the introns except for the signal peptide domain. The numbers of nucleotide substitutions per site (KN) for the UTRs and the introns were approximately one-quarter of the numbers of nucleotide substitutions per synonymous site (KS) for the protein-coding regions and were at the same level as the KN value of T. gramineus and T. flavoviridis TATA box-binding protein (TBP) genes, indicating that the protein-coding regions of PLA2 isozyme genes are unusually variable and that the UTRs including the introns of venom gland PLA2 isozyme genes have evolved at similar rate to those of non-venomous genes. The numbers of nucleotide substitutions per non-synonymous site (KA) values were close to or larger than the KS values for the protein-coding regions in venom gland PLA2 isozyme genes, indicating that the protein-coding regions of snake venom gland PLA2 isozyme genes have evolved via accelerated evolution. Furthermore, the evolutionary trees derived from the combined sequences of the 5' and 3' UTRs and the signal peptide domain of cDNAs were in accord with the consequences from taxonomy. In contrast, the evolutionary trees from the mature protein-coding region sequences of cDNAs and from the amino acid sequences showed random patterns. Estimations of nucleotide divergence of genes and the phylogenetic analysis reveal that snake venom group IJ PLA2 isozyme genes have been evolving under adaptive pressure to acquire new physiological activities.

Amino Acid Sequence↗
PubMedDate not supplied

Opioid activities of morphiceptin-like peptides latent in various natural proteins.

The Tyr-Pro-Phe peptide sequence, an N-terminal tripeptide fragment of opioid peptide morphiceptin, was searched on the database SEQDB (Peptide Institute, Osaka). More than 30 proteins were drawn in a list with 15 amino acid varieties at the position adjacent to Phe. Seven morphiceptin-like peptides with the H-Tyr-Pro-Phe-Xxx-NH2 sequence, where Xxx denotes the selected amino acids (Ala, Asp, Gly, Gln, Lys, Thr and Tyr), have been synthesized. Together with the side-chain protected analogs [Asp(OBzl), Lys(Z), and Thr(Bzl)], they have been evaluated for opioid activities. For the mu opioid receptors to which morphiceptin binds specifically and selectively, analogs with Xxx = Asp, Lys, Ala, Thr, Gln, Tyr and Gly showed a considerably weaker binding affinity than morphiceptin. In contrast, the Thr(Bzl) derivative demonstrated an affinity ten times greater than morphiceptin. Because of an extremely weak affinity for the delta receptors, its mu-selectivity became very high (260-fold). The present results and the increased activity of [Val4]morphiceptin (Sakaguchi et al., 36) indicate that the mu receptors tolerate the hydrophobic or aromatic residue at the site corresponding to position 4 of morphiceptin. When the circular dichroism (CD) spectra are compared between active and inactive analogs, no significant difference is found in both water and methanol. This suggests that the activity of morphiceptin analogs with the Tyr-Pro-Phe sequence is mainly determined by the structural characters of the amino acid residue in position 4 rather than by the molecular conformation. The results suggested a possible formation of morphiceptin-like peptides in various protein digests.

Amino Acid Sequence↗
PubMedDate not supplied

Enzyme-inhibitory conformation of dipeptides containing sterically constrained amino acid 2,3-methanophenylalanine.

Dipeptides containing 2,3-methanophenylalanine, a sterically constrained amino acid with alpha,beta-cyclopropane ring, showed fairly strong inhibitory activity for the hydrolysis of Ac-L-Tyr-OEt by chymotrypsin. Kinetic analyses of the inhibition by dipeptides, H-inverted delta E Phe-Leu (or Phe)-OMe (or OH), indicated the mode of inhibition to be competitive. Comparative analyses of the inhibitory constants Ki have clarified several structural elements necessary to elicit an inhibitory activity. Those include the (2R,3S)-configuration of the inverted delta E Phe residue, the phenyl side chain at position 2 and the C-terminal methylesterification. These structural conditions suggested that the peptides are in specific inhibitory conformation. In the conformational analyses of these dipeptide inhibitors by a high resolution 1H-NMR (270 MHz), the measurement of enhancements of the nuclear Overhauser effect indicated that an intramolecular hydrophobic bonding exists between the inverted delta Phe-phenyl and ester-methyl to construct the hydrophobic core in the molecule. It was suggested that this hydrophobic core interacts with the chymotrypsin S2 site and prevents the hydrolysis of methyl ester. The Leu2 or Phe2 interacts with the enzyme S1 site. The structure of dipeptides containing 2,3-methanophenylalanine has been characterized as an enzyme-inhibitory conformation that interacts with the enzyme at its catalytic center.

Chymotrypsin↗
PubMedDate not supplied

Design and synthesis of dimeric analogs of neurokinin A and B: effect of dimerization of COOH-terminal heptapeptides on receptor selection.

Dimeric analogs of neurokinin A and neurokinin B COOH-terminal heptapeptides were synthesized in order to examine the effect of ligand dimerization on the receptor selection. Dimerization was carried out at the NH2-terminus of peptides with succinic acid, yielding succinyl bis[Asp-Ser-Phe-Val-Gly-Leu-Met-NH2] (D-NKA4-10) and succinyl bis[Asp-Phe-Phe-Val-Gly-Leu-Met-NH2] (D-NKB4-10). In the assay using rat vas deferens (RVD), it was found that the deletion of the NH2-terminal tripeptide from native neurokinin A or B enhances the activity 1.5- to 8-fold, resulting in formation of NK-2 receptor specific ligands NKA4-10 and NKB4-10. When dimeric analogs of these shortened peptides, namely D-NKA4-10 and D-NKB4-10, were examined in RVD and guinea pig ileum (GPI), they were fairly potent in GPI, but not in RVD. Under conditions in which the NK-1 receptors in GPI were desensitized with NK-1 specific substance P methyl ester, dimers reduced the activity drastically, while the corresponding monomers exhibited unchanged activity. These results suggest that dimerization of the COOH-terminal heptapeptide of neurokinins changes the receptor selection of peptides from NK-2 to NK-1, and that the NK-1 receptor has a structure favorable to a dimeric peptide ligand.

Amino Acid Sequence↗