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M Chorev

Publications and source records attributed to M Chorev.

At least 127 records · Page 7Linked to original sources
PubMed1986

Ketomethylene pseudopeptide analogues of substance P: synthesis and biological activity.

Two pseudopeptide analogues [Bz-(RS)Phe8 psi (COCH2)Gly9]SP8-11 (I) and [pGlu6,(RS)Phe8 psi (COCH2)Gly9]SP6-11 (II) of the substance P related C-terminal hexapeptide [pGlu6]SP6-11 were prepared as follows. The pseudodipeptidic unit H(RS)Phe psi (COCH2)GlyOH was synthesized by using a modified Dakin-West reaction between Bz-Phe-OH and monomethyl succinoyl chloride. The N alpha-protected pseudopeptidic unit was then incorporated into the appropriate peptide by using various coupling methods. The two pseudopeptide analogues were purified, characterized, and tested for their biological activity and inhibitory effect on SP degrading enzymes. Analogue II was a full agonist contracting the isolated guinea pig ileum with a potency of 70% compared to the parent hexapeptide [pGlu6]SP6-11. It was also a potent inhibitor of SP degrading activity in rat diencephalon membranes with a Ki of 20 microM whereas analogue I was a weak inhibitor.

Animals↗
PubMed1986

[pGlu6,Pro9]SP6-11, a selective agonist for the substance P P-receptor subtype.

Substitution of a single amino acid residue, proline for glycine-9 in [pGlu6]SP6-11, a hexapeptide analogue of substance P, confers on the peptide selective agonist activity toward the SP-P receptor subtype. [pGlu6,Pro9]SP6-11 had 20% and 75% of the activity of [pGlu6]SP6-11 in stimulating, respectively, K+ release from rat parotid slices and contraction of the isolated guinea pig ileum, via the SP-P receptor subtype. In contrast, [pGlu6,Pro9]SP6-11 had substantially reduced activity on SP-E systems such as the hamster urinary bladder and rat duodenum, being about 20-fold less potent than [pGlu6]SP6-11 and 200-670-fold less potent than neurokinin B. In the guinea pig ileum [pGlu6,Pro9]SP6-11 had very low activity on the neuronal tachykinin receptor, being 325 times less potent than [pGlu6]SP6-11 and 1000 times less potent than neurokinin B. Because of its discrimination between the muscular and neuronal receptors in the guinea pig ileum (muscular/neuronal potency ratio = 600), [pGlu6,Pro9]SP6-11 can be used to specifically desensitize the muscular receptor of this tissue. This procedure enables a selective and sensitive bioassay of the neuronal receptor.

Animals↗
PubMed1985

Desensitization of substance P-induced K+ release in rat parotid.

Challenge of rat parotid slices with substance P or its analogs, at concentrations which cause less than maximal response resulted in the transient release of K+ into the medium. Reuptake of the released K+ into the cell was accompanied by a parallel decrease in the biologically active concentration of the peptide in the medium, indicating that at low concentrations inactivation of the peptide is a mechanism for termination of the substance P response. At concentrations of substance P and its analogs which are higher than needed for a maximal response, a second mechanism for the termination of the response enters into play, resulting in desensitization of the response to substance P. Desensitization was specific for substance P and was not influenced by activation of the cholinergic or alpha-adrenoceptors. Inactivation of the peptide by proteolytic breakdown does not take part in the development of desensitization to substance P.

Animals↗
PubMed1985

Inhibition of substance P degradation in rat brain preparations by peptide hydroxamic acids.

A peptidase activity of rat diencephalon membranes, which acts on the C-terminal hexapeptide sequence of substance P, was characterized using the radiolabeled substrate N alpha-[( 125I]iododesaminotyrosyl)-substance P (6-11)-hexapeptide. This activity presents certain characteristics similar to those of the substance-P-degrading enzyme purified from human brain by Lee et al. [Eur. J. Biochem. 114, 315-327 (1981)]. It is inhibited by metal chelators and some thiol reagents, but is insensitive to inhibitors of serine proteases and aminopeptidases. The activity is different from angiotensin-converting enzyme and enkephalinase, since it is not affected by specific inhibitors of these enzymes. Substance P and substance P C-terminal fragments longer than the pentapeptide inhibited the degradation of the radiolabeled substrate with inhibition constants around 200 microM. Short fragments of the substance P sequence, such as Boc-Phe-Phe-OMe and Boc-Phe-Phe-Gly-OEt, were also found to inhibit the degradation of the substrate. When the metal-chelating hydroxamic acid moiety was attached to the carboxyl terminus of these short peptides, potent inhibitors of the substance-P-degrading activity were obtained, with inhibition constants in the micromolar range. The most potent of these compounds, iododesaminotyrosyl-Phe-Phe-Gly-NHOH (IBH-Phe-Phe-Gly-NHOH), is a competitive inhibitor, with a Ki value of 1.9 microM. The degradation of substance P by rat diencephalon slices was inhibited to the same extent (40-50%) by IBH-Phe-Phe-Gly-NHOH (20 microM) and by phosphoramidon (1 microM). A combination of both reagents reduced the degradation rate by 75-80%, suggesting that both enkephalinase and the substance-P-degrading activity are involved in the metabolism of substance P in this preparation. IBH-Phe-Phe-Gly-NHOH seems to be quite specific for the latter enzyme, since at a high concentration (0.1 mM) it did not affect the degradation of the radiolabeled substrate by alpha-chymotrypsin, papain, or thermolysin.

Animals↗
PubMed1985

N-Bromoacetyl-amino-cyanopindolol: a highly potent beta-adrenergic affinity label blocks irreversibly a non-protein component tightly associated with the receptor.

A new chemical affinity label for the beta-adrenergic receptor, based on the structure of pindolol, has been synthesized and iodinated with 125I. The compound, N-bromoacetylamino-cyanopindolol (BAM-CYP), has an apparent dissociation constant of 44 +/- 7 pM towards the turkey erythrocyte membranes. This compound blocks irreversibly both the ability of beta-adrenergic receptors to bind 125I-cyanopindolol and the ability of beta-receptors to activate adenylate cyclase in the presence of beta-agonists. Furthermore, the irreversible binding of BAM-CYP to half of the beta-receptor sites abolishes the ligand binding activity of all the sites. These findings suggest that the beta-receptor is oligomeric in its native state. Although 125I-BAM-CYP blocks irreversibly and specifically the beta-adrenergic receptor, it does so by labeling a non-protein component, most probably a water-soluble lipid. The labeling is stereospecific since it is prevented by l-propranolol and not by d-propranolol. It is suggested that this lipid is tightly associated with the receptor in close proximity to the binding site. It is also suggested that this water-soluble lipid fraction may prove crucial for the optimal interaction between the beta-adrenergic receptor and the components of adenylate cyclase.

Adenylyl Cyclase Inhibitors↗
PubMed1985

Neurokinin B is a preferred agonist for a neuronal substance P receptor and its action is antagonized by enkephalin.

Receptor specificity of the substance P-related peptides neurokinin A and neurokinin B was studied in the isolated guinea pig ileum. Substance P and the recently discovered neurokinins elicit contraction of the ileum both directly through action on a muscle cell receptor and indirectly through stimulation of a neuronal receptor, leading to release of acetylcholine, which causes muscle contraction via muscarinic receptors. Two specific assay procedures for the function of the neuronal receptor were developed. The muscular receptor was inactivated either by desensitization with the selective agonist substance P methyl ester or by receptor blockade with the selective antagonist [Arg6, D-Trp7,9, Me-Phe8]substance P-(6-11) hexapeptide. Both procedures revealed that the neuronal receptor is clearly distinct from the muscular receptor, since it exhibits different agonist specificity and is insensitive to antagonists of the muscular receptor. Neurokinin B was found to be the most potent agonist (EC50 = 1 nM) for the neuronal receptor. Furthermore, [D-Ala2, Met5]enkephalinamide inhibited in a naloxone-sensitive manner the effect of neurokinin B mediated via the neuronal receptor. These results suggest that the different mammalian tachykinins can play specific physiological roles by virtue of their distinct receptor specificities.

Animals↗
PubMed1984

Ion-exchange chromatographic assay of peptidases acting on the C-terminal hexapeptide sequence of substance P.

A rapid and sensitive assay for peptidases acting on the C-terminal hexapeptide sequence of the neuropeptide substance P is described. The radiolabelled substrate, N alpha-[125I]desaminotyrosyl-substance P (6-11) is easily prepared by coupling commercially available radioiodinated Bolton-Hunter reagent with substance P (6-11). Peptidase activity is determined by quantitative separation of the degradation products from the intact substrate on small QAE-Sephadex columns. The assay has been used to measure degradation of the substrate by rat parotid and diencephalon slices. The peptidase activity in the latter system was inhibited by substance P and substance P fragments and was sensitive to metal chelators and thiol reagents.

Amino Acid Sequence↗
PubMed1984

Substance P degrading systems of rat parotid and hypothalamus.

Inactivation of substance P and its C-terminal hexapeptide analog [p-Glu6]substance P6-11 was studied in rat parotid and hypothalamic slices. It was found that in the parotid slice system the decay of substance P induced K+ release occurs concurrently with a decrease in the biologically active concentration of the peptide in the medium. The inactivation was further studied using [p-Glu6]substance P6-11 as substrate in the parotid and in the hypothalamic slice systems. In both tissue preparations the hexapeptide is degraded to small peptide fragments by metalloendopeptidase. Separation of the peptide fragments by high performance liquid chromatography and determination of their amino acid composition showed that in the hypothalamic slice system the major cleavage of the hexapeptide analog occurs between Phe8-Gly9 with minor cleavage sites between Phe7-Phe8 and Gly9-Leu10. In the rat parotid slice system the major cleavage occurs between Gly9-Leu10 with a minor cleavage site between Phe7-Phe8. The degradation of the hexapeptide analog in the hypothalamic system was inhibited 77% and 67% by treatment with 1 mM p-chloromercuriphenylsulfonate and p-chloromercuribenzoate, respectively, whereas in the parotid system these reagents inhibited the degradation of the hexapeptide only by 15% and 8%. These results may indicate that different proteases in the parotid and hypothalamus are involved in degradation of substance P. Kinetic studies, including the use of various inhibitors as well as competition by the peptide hormones somatostatin, LHRH, TRH and Leu-enkephalin-NH2, revealed that in both tissues the hexapeptide analog is a preferred substrate for degradation by protease of considerable specificity towards the C-terminal sequence of substance P. It is suggested that this metalloendopeptidase may be important in the termination of the substance P response.

Amino Acid Sequence↗
PubMed1983

Effect of opiates on human colonic adenylate cyclase activity.

To elucidate a possible mechanism whereby opiates affect human intestinal fluid secretion, opiate effects on human basal and stimulated colonic adenylate cyclase activity were determined. Morphine (10 microM) and naloxone (1 microM) did not affect basal colonic adenylate cyclase activity: 32.6 +/- 2.6 (n = 23; X +/- S.E.) pmol cAMP/mg protein per 10 min or its stimulation induced by sodium fluoride or VIP. However, morphine inhibited the stimulation induced by prostaglandin E2, an effect which was blocked by naloxone. Synthetic enkephalins and metabolically stable retro inverso enkephalins also prevented PGE2-induced stimulation of colonic adenylate cyclase activity. The addition of calcium (0.1 mM) decreased the basal and PGE2-stimulated enzyme activities by 35% and 50%, respectively, regardless of the presence or absence of morphine. These results suggest that morphine and synthetic enkephalins do not affect basal human colonic adenylate cyclase activity but inhibit its stimulation induced by PGE2. This effect may be one of the mechanisms whereby opiates affect intestinal fluid transport.

Adenylyl Cyclases↗
PubMed1983

Synthesis of partially modified retro-inverso substance P analogues and their biological activity.

Partial retro-inverso modification of a single peptide bond was applied to pGlu-Phe-Phe-Gly-Leu-Met-NH2 (I), a C-terminal hexapeptide analogue of the neuropeptide substance P. Two analogues with reversed peptide bonds, between the pGlu-Phe and Phe-Gly residues, were prepared, purified and characterized. The analogue gpGlu-(RS)-mPhe-Phe-Gly-Leu-Met-NH2 (II) was devoid of either agonistic or antagonistic activity. The second pseudopeptide analogue, i.e., pGlu-Phe-gPhe-mGly-Leu-Met-NH2 (III), was found to be a full agonist with 22% of the potency of I in the guinea pig ileum assay.

Amino Acid Sequence↗
PubMed1983

Partially modified retro-inverso peptides. Comparative Curtius rearrangements to prepare 1,1-diaminoalkane derivatives.

Several synthetic routes are reported to prepare the hetero diprotected 1,1-diaminoalkanes from N-acylated amino acids or peptides for incorporation into partially modified retro-inverso peptides. The Curtius rearrangement was carried out on the N-protected aminoacyl azides obtained from the N-protected aminoacyl hydrazide by nitrosyl chloride or by sodium azide reaction with an appropriate mixed carboxylic carbonic acid anhydride. The resulting isocyanate was allowed to react with alcohol to give a urethane-type protecting group or, via a "one-pot" approach, directly with a carboxyl carrying component to yield the modified (reversed) peptide bond. The carboxyl component can be either an N-acylated amino acid or a malonic acid. The more standard route involves selective deprotection of the 1,1-diaminoalkane residue followed immediately by coupling with a carboxyl component to yield the same modified peptide derivative.

Chemical Phenomena↗
PubMed1981

Field desorption mass spectrometry. II. Potassium cationization field desorption mass spectrometry of some penta- and hexapeptides derived from substance P.

In this article we present preliminary results of the application of potassium cationized field desorption mass spectrometry as an additional technique for the elucidation of structure and evaluation of purity of oligopeptides such as C-terminal penta- and hexapeptide analogs of substance P. In the resultant mass spectra both a protonated and a cationized molecular ion, MH+ and MK+ respectively, were observed. The m/z values of the two peaks were in agreement with the calculated molecular weights. The ratio between the relative abundancies of these ions (MH+/MK+) was found to be characteristic of the particular peptide and thus useful in the assessment of their purity. Among the 13 peptides studied, only two gave pyrolytic fragmentation leading to a more complex spectra.

Mass Spectrometry↗
PubMed1980

Peptide sweeteners. 3. Effect of modifying the peptide bond on the sweet taste of L-aspartyl-L-phenylalanine methyl ester and its analogues.

A series of analogues designed to assess the importance of the amide bond in the dipeptide sweetener L-aspartyl-L-phenylalanine methyl ester has been synthesized and tested. The peptide bond was methylated, replaced by an ester bond, or reversed. all of these modifications produced compounds that did not have a sweet taste. We conclude that the steric, electronic, and directional characteristics of the amide bond are essential for biological activity in the dipeptide sweeteners.

Aspartame↗
PubMed1980

Peptide sweeteners. 4. Hydroxy and methoxy substitution of the aromatic ring in L-aspartyl-L-phenylalanine methyl ester. Structure-taste relationships.

A series of analogues of the dipeptide sweetener L-aspartyl-L-phenylalanine methyl ester having hydroxy and/or methoxy substitution on the aromatic ring was synthesized and tasted. The introduction of a methoxy group in the para position of the aromatic ring of the peptide sweetener is crucial to the reduction or destruction of the sweet taste. The effects of substituents in the ortho or meta position are not as pronounced. In the case of o-methoxy substitution, the resulting analogue is only slightly less sweet than the parent dipeptide sweetener.

Humans↗