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At least 1,207 records · Page 67Linked to original sources
PubMed1984

Backbone side chain interactions in peptides. I. Crystal structures of model dipeptides with the Pro-Ser sequence.

The preferential occurrence of amino-acid residues having short polar side-chain within beta-folded regions of crystallized proteins suggests the existence of some stabilizing interaction involving the side polar function. Three model dipeptides tBuCO-L-Pro-L-Ser-NHMe 1, tBuCO-L-Pro-D-Ser-NHMe 2 in the pure enantiomeric a and racemic b forms, and iPrCO-L-Pro-D-Ser-OMe 3 have been investigated in the solid state by X-ray crystallography. Homo and heterochiral sequences 1 and 2 are folded in the beta I and beta II types, respectively, whereas 3 obviously accommodates an open conformation. Besides the i + 3 leads to i hydrogen bond typical of beta-bends in 1, 2a, and 2b, the Ser NH group in all four crystal structures is a proton donor to the lone orbitals of the Ser O gamma oxygen atom. The result is that the disposition of the Ser C alpha--C beta bond corresponds to the rotamer III (chi 1 congruent to 60 degrees). As shown by the crystal structure of 3, the intra-Ser NH. . .O gamma hydrogen bonding is not restricted to beta-folded Pro-Ser sequences. Therefore, this interaction is not only a stabilizing factor for beta-turns but it is also probably responsible for the already mentioned stability of rotamer III for the Ser C alpha--C beta bond in peptides and protein.

Dipeptides↗
PubMed1984

Backbone side chain interactions in peptides. II. Solution study of serine-containing model dipeptides.

The high content of serine in beta-folded regions of proteins may be the consequence of some specific interaction between the peptide backbone and the hydroxyl group of the Ser side-chain. The resolution of the X-ray structures of three peptides with the Pro-Ser sequence protected on both ends by amide and/or ester functions indicates that the Ser NH bond is a proton donating group to the Ser O gamma atom in the solid state. The present study deals with spectroscopic investigations on five Ser-containing model dipeptides with the L-Pro-D-Ser 1, L-Pro-L-Ser 2, L-Ala-L-Ser 3, L-Ser-L-Ala 4 and L-Ser-Gly 5 sequences protected on their N and C-termini by tBuCO and NHMe groups, respectively. The N--H. . .O gamma interaction found in the solid state of 1 and 2 is at least partly retained in solution and its occurrence in X-Ser sequences is fully compatible with beta-folding. The same is not true for Ser-X sequences in which the competition between the typical beta-turn i + 3 leads to i hydrogen bond and the N--H . . . O gamma interaction results in lower contents of beta-folded conformers. Because of this latter interaction, the rotamer III (chi 1 congruent to 60 degrees) is the most frequent disposition of the Ser C alpha--C beta bond in all five derivatives.

Circular Dichroism↗
PubMedDate not supplied

[Biological role of histidine dipeptides in excitable tissues].

The biological role of the histidine dipeptide carnosine in the cells of olfactory bulb and muscular tissue was studied. In the muscle, carnosine directly interacts with peroxides formed in the tissue that deteriorate the structure and function of membranes, and participates in maintaining the muscle in a functionally active state.

Animals↗
PubMed1983

Structure of N-tert-butyloxycarbonyl-D-leucyl-L-phenylalanylethanolamide. An N alpha-protected analogue of the COOH-terminal dipeptide of linear gramicidins.

Solid state conformational analysis of N-tert-butyloxycarbonyl-D-leucyl-L-phenylalanylethanolamide (t-Boc-D-Leu-L-Phe-EA), an N alpha-protected analogue of the COOH-terminal dipeptide of linear gramicidins, carried out by x-ray diffraction, has indicated that the molecules are characterized by an N-H...O = C intramolecularly hydrogen-bonded chain reversal of the beta-turn II' type. One of the two independent molecules in the asymmetric unit shows an additional intramolecular hydrogen bond of the O-H...O = C type, linking the hydroxyl function of the COOH-terminal ethanolamide moiety to the carbonyl oxygen of the urethane N-protecting group. This is the first experimental evidence for a beta-turn conformation fused with the oxy analogue of an alpha-turn. The results of an investigation in a solvent of low polarity (deuteriochloroform), using infrared absorption and 1' nuclear magnetic resonance, strongly support the view that an intramolecularly hydrogen-bonded beta-turn conformation is the most populated conformation of t-Boc-D-Leu-L-Phe-EA molecules at high dilution. In the self-association process, taking place at high concentration, the urethane and peptide NH groups are involved as hydrogen-bonding donors.

Amino Acid Sequence↗
PubMed1983

[Concentration of free amino acids and homocarnosine dipeptide in the cerebrospinal fluid of children with hydrocephalus].

The content of free amino acids and the dipeptide homocarnosine was examined in the cerebrospinal fluid of children with post-meningitis hydrocephalus. Of 17 identified amino acids the levels of threonine, methionine, leucine, alanine, lysine, histidine, glutamic acid and GABA appeared to be sharply changed. The homocarnosine level in the hydrocephalic children's CSF was found to be 10, and in hydrocephalic children with idiocy, 18 times higher than in the control.

Amino Acids↗
PubMed1984

Biologically active halophthaloylpeptides. I. Synthesis of tetrachlorophthaloylamino acids and dipeptide derivatives.

The synthesis of a series of tetrachlorophthaloylamino acids and some of the corresponding methyl esters is described. Coupling of tetrachlorophthaloylamino acids with amino acid methyl esters by the N,N'-dicyclohexylcarbodiimide method yielded the desired tetrachlorophthaloyldipeptide methyl esters. All of the synthesized tetrachlorophthaloylamino acids, esters and some dipeptide methyl esters were found to be active against a number of microorganisms.

Anti-Bacterial Agents↗
PubMed1982

Histamine synthesis, imidazole dipeptides, and wound healing.

The relationships among anserine (beta-alanyl-1-methyl-L-histidine), carnosine (beta-alanyl-L-histidine), free histidine, and histamine metabolism were examined in rats wounded by dorsal skin incision. Following wounding, rats were treated with either a histamine liberator (compound 48/80) or a histidine decarboxylase inhibitor (4-imidazolyl-3-amino-2-butanone). The liberator greatly enhanced wounded skin-breaking strength and collagen deposition at the wound site, while the histidine decarboxylase inhibitor reduced skin-breaking strength and collagen deposition. In the second experiment of this study, histamine or histidine treatment was shown to prevent trauma-induced reductions of tissue carnosine but was less effective in ameliorating tissue anserine loss. The results illustrate an interaction between imidazole dipeptides and stress and suggest that carnosine acts as a histidine reserve in relation to histamine synthesis during trauma.

Animals↗
PubMed1980

Empirical calculations on cyclic dipeptides. Conformations of aspartic acid, glutamic acid and histidine residues.

Empirical conformational energy calculations were carried out for the dipeptides cyclo-(L-Asp-L-His) and cyclo-(L-Glu-L-His). The side chain conformations have been studied for various DKP ring structures, demonstrating that distortions can modify the stability of some conformations by favouring peptide backbone-side chain or side chain-side chain interactions. The carboxylic side chain of Asp and Glu residues can induce specific interactions with the imidazole ring or the peptide bond of the DKP ring which are not found for Ser or Thr. The necessity of including solute--solvent interactions to account for a more realistic conformational behaviour is discussed.

Dipeptides↗
PubMed1995

Novel dipeptide aldehydes are proteasome inhibitors and block the MHC-I antigen-processing pathway.

Class I MHC (MHC-I) molecules present peptides derived from Ag that are processed in the cytosol. The proteasome is a multicatalytic protease complex that is present in the cytosol and has been implicated in cytosolic Ag processing. Novel dipeptide aldehydes were designed, synthesized, and demonstrated to specifically inhibit the chymotrypsin-like protease activity of isolated proteasomes, but produced relatively little inhibition of cathepsin B, a vacuolar cysteine protease. The inhibitors were membrane permeable and inhibited intracellular cleavage of a membrane-permeable fluorogenic substrate of the chymotrypsin-like proteasome activity. When a model Ag, OVA, was introduced into the cytoplasm of M12.B6 murine B cells by electroporation, the proteasome inhibitors blocked its processing for subsequent presentation by MHC-I molecules. The inhibitors had little effect on class II MHC processing of exogenous Ag. The potencies of different inhibitors for blockade of MHC-I Ag processing correlated directly with their potencies for inhibition of the chymotrypsin-like proteasome activity. In contrast, conventional inhibitors of vacuolar cysteine proteases (e.g., leupeptin and benzyloxycarbonyl-Phe-Ala-CHN2) had little effect on MHC-I processing or the chymotryspin-like activity of isolated proteasomes. These results directly demonstrate that inhibition of proteasome activity blocks MHC-I Ag processing, confirming a role for proteasomes in this pathway. Moreover, they suggest that the chymotrypsin-like activity of the proteasome may be of major importance to the cytosolic processing of at least some Ag.

Aldehydes↗
PubMed1993

[Synthesis of formyl (acetyl) amino acid and dipeptide derivatives of amino ketones].

Since alpha-acetylaminoacetophenones are known to have antihepatitis activity, a series of aminoacyl and dipeptidyl derivatives were synthesized by replacement of the acetyl group with amino acid and dipeptide acyl groups or by changing the substituents on the benzene ring. Thirty-four compounds were submitted to pharmacological screen for antihepatitis and/or antipeptic ulcer activity. The results showed that the presence of methylene-dioxy group on the benzene ring showed favorable influence on the SGPT-lowering activity of the compounds.

Acetophenones↗
PubMed1994

Functional alpha-tropomyosin produced in Escherichia coli. A dipeptide extension can substitute the amino-terminal acetyl group.

Unlike the muscle protein, alpha-tropomyosin expressed in Escherichia coli does not bind actin, does not exhibit head-to-tail polymerization, and does not inhibit actomyosin ATPase activity in the absence of troponin. The only chemical difference between recombinant and muscle tropomyosins is that the first methionine is not acetylated in the recombinant protein (Hitchcock-De-Gregori, S.E., and Heald, R. W. (1987) J. Biol. Chem. 262, 9730-9735). We expressed three fusion tropomyosins in E. coli with 2, 3, and 17 amino acids fused to its amino terminus. All three fusions restored actin binding, head-to-tail polymerization, and the capacity to inhibit the actomyosin ATPase to these unacetylated tropomyosins. Unlike larger fusions, the small fusions of 2 and 3 amino acids do not interfere with regulatory function. Therefore the presence of a fused dipeptide at the amino terminus of unacetylated tropomyosin is sufficient to replace the function of the N-acetyl group present in muscle tropomyosin. A structural interpretation for the function of the acetyl group, based on our results and the coiled coil structure of tropomyosin, is presented.

Actins↗
PubMedDate not supplied

[The effect of tyrosine-containing dipeptide on neuroglycopenia-induced changes in the activities of the sympathetic nervous system and of the systemic hemodynamics in waking rats].

A modulatory role of the precursor of catecholamines--tyrosine (TYR)--in 2-deoxyglucose (2DG)-induced changes in blood pressure (BP), renal sympathetic nerve activity (renSNA), plasma levels of epinephrine (EPI) and norepinephrine (NE), total spillover of NE (TSO), and sensitivity of baroreceptor reflex (SBR) is studied. Chronically instrumented male Wistar rats were injected with 2DG (125 - 500 mg/kg iv), and BP, heart rate (HR), renSNA, TSO, EPI, NE, plasma clearance NE (CINE) and SBR were monitored before and after 2DG administration. The responses to 2 DG in control rats were compared with those in rats pretreated with tyrosile-tyrosine dipeptide (TYR-TYR). SBR was estimated by bolus i.v. sodium nitroprusside injection. 2DG evoked an increase in renSNA by 23%, 40-fold and 2.5-fold increases in EPI and NE concentrations, 2,7-fold increase in TSO, a decrease in HR by 5% in 45 min without reliable changes in BP and CINE. TYR-TYR administration did not affect 2DG-induced changes in HR, TSO, EPI and NE concentrations, but potentiated changes in renSNA by 53% and significantly increased BP by 10%. 2DG produced an increase in the chronotropic (by 87%) and sympathetic (by 72%) components of SBR. TYR-TYR restored the normal values of SBR in 2DG-treated rats. Thus, tyrosine modulates 2DG-induced changes in hemodynamic parameters and renSNA and normalizes SBR via central mechanisms.

Analysis of Variance↗
PubMed1996

Effect of adamantylamide dipeptide on reinfection resistance after primary infection eradication in experimental Schistosomiasis mansoni.

The immunomodulatory effect of adamantylamide dipeptide (AdDP) was tested in Schistosoma mansoni-infected challenged mice and infected praziquantel-treated (2 x 500 mg/kg) challenged animals. In AdDP-treated mice, the drug was given 58 days post infection of mice with 120 S. mansoni cercariae, challenged with 240 cercariae one day after treatment, while in praziquantel-treated mice, the drug was given 44 days post infection, two weeks post treatment (58 days post infection) they were given AdDP in the same dose and one day later challenged with the same cercarial load. AdDP increased the resistance against reinfection (90.3% vs. 83.5% in infected challenged control). The significant increase in resistance against reinfection was accompanied by significant increase in the percentage of lymphocytes forming EAC rosettes. Mice cured of their primary infection by praziquantel showed a significant reduction in percent resistance, hepatic granuloma size and intragranulomal Thy+ 1,2 and Lyt+ 1 T cells. In mice treated with both praziquantel and AdDP, resistance to reinfection was significantly higher than in mice treated with praziquantel only (89.29% vs. 62.13%) reaching a level comparable to that recorded in infected-challenged controls. Meanwhile granuloma size was not significantly different from that in the infected-challenged controls with a significant rise in Lyt+ 1 T cells. Data may suggest a role for granuloma as a mechanical obstacle and/or as a T cell-mediated reaction in maintenance of resistance to reinfection. A role for B lymphocytes should be considered as the rise of percent resistance to reinfection in mice treated with AdDP alone was accompanied by a significant increase in the percentage of B lymphocytes forming EAC rosettes. Moreover, findings may suggest the use of AdDP together with specific chemotherapy in endemic areas where reinfection and repeated treatment with its consequences are of common occurrence.

Adjuvants, Immunologic↗
PubMed1997

Effect of histidine-containing dipeptides on isolated heart under ischemia/reperfusion.

The protective effects of carnosine and related compounds on isolated rat heart were studied under experimental ischemia. The ability of carnosine to suppress significantly the development of ischemic reperfusion contracture and to support the restoration of the contractile force during reperfusion were shown. At the same time, a decrease of myoglobin and nucleoside release from myocytes was observed, this indicating a membrane-protecting effect of carnosine. Methylation of carnosine at the N1 or N3 atom of the imidazole ring significantly decreased the protective effect; the substitution of beta-alanine with gamma-aminobutyric acid (resulting in formation of homocarnosine) actually augmented ischemic damage to the heart. Acetylation of carnosine at the beta-amino group amplified the membrane-protecting properties of the molecule, the acetylated derivative of carnosine also showing the ability to induce contractile activity of the ischemic heart. Histidine alone or in combination with beta-alanine and sodium acetate had no effect, while acetylhistidine showed a significant protective effect during reperfusion. The comparison of the effects of natural histidine-containing dipeptides versus synthetic antioxidants indicates that the anti-ischemic effect of carnosine and acetylcarnosine involves antiradical and membrane-protecting mechanisms; nevertheless, the effect cannot be reduced to these mechanisms alone. The observed phenomena of heart muscle protection by acetylated derivatives of carnosine and anserine under ischemia correlates with the preferential localization of these compounds in high quantities in the myocardium.

Animals↗
PubMed1977

[Inhibition of passive cutaneous anaphylaxis by dipeptides].

The action of some dipeptides (Lalpha-alanyl-histidine, Lbeta-alanyl-histidine, histidyl-leicine and glycyl-histidine), and histidine on passive cutaneous anaphylaxis of guinea pigs was studied. Lbeta-alanyl-histidine (karnosine) and Lalpha-alanyl-histidine proved to inhibit the passive cutaneous anaphylaxis. Histidyl-leicine, glycyl-histidine, and histidine failed to produce any inhibitory effect on passive cutaneous anaphylaxis.

Allergens↗
PubMedDate not supplied

[The pharmacokinetics of the dipeptide analog of piracetam with nootropic activity GVS-111 and of its basic metabolites].

The pharmacokinetics of a new nootropic dipeptide analog of piracetam-N-phenylacetyl-L-prolylglycine (GWS-111) and its main metabolites were studied in rats by means of high performance liquid chromatography and gas-liquid chromatography. The compound under study showed a greater resistance to an enzymatic effect than natural neuropeptides. In addition to an unchanged compound three of its metabolites were found in the blood plasma of the rats. One of them, cyclo-Pro-Gly was an active metabolite of GWS-111.

Animals↗
PubMed1996

[Glutamine dipeptide attenuate mucosal atrophic changes and preservation of gut barrier function following 5-FU intervention].

Traditional parenteral nutrition (PN) and chemotherapy may lead to changes mucosal morphology and gut barrier function. To investigate the effects of alanyl-glutamine on intestinal mucosal morphology and gut barrier function in PN-fed rats challenged with 5-FU male Wistar rats were central catheterized and randomily divided into two groups: PN group (n = 10) that received traditional parenteral nutrition solution only, and Ala-Gln group (n = 10) that received glutamine dipeptide enriched nutritional solution (3% Ala-Gln). The rats were maintained on their respective diets for 7 days. 5-FU (75 mg/kg) was injected intraperitoneally at 8 am on day 4. All rats were gavaged with lactulose (100 mg) and mannitol (50 mg) in 2ml before and three days after administration of 5-FU. Ala-Gln group maintained serum glutamine concentration, intestinal mucosal morphology. While bacterial translocation rates in ala-Gln group was 30%, in PN group was 90% (P < 0.05). Similar intestinal permeability was observed on day 3 in both groups. The control group had a significantly increased intestinal permeability on day 7 (P < 0.05), while Ala-Gln group maintained the intestinal permeability. It was suggested that alanyl-glutamine maintained intestinal morphology and gut barrier function in PN-fed rats challenged with 5-FU.

Animals↗