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PubMed2005

Electrostatic DFT map for the complete vibrational amide band of NMA.

An anharmonic vibrational Hamiltonian for the amide I, II, III, and A modes of N-methyl acetamide (NMA), recast in terms of the 19 components of an external electric field and its first and second derivative tensors (electrostatic DFT map), is calculated at the DFT(BPW91/6-31G(d,p)) level. Strong correlations are found between NMA geometry and the amide frequency fluctuations calculated using this Hamiltonian together with the fluctuating solvent electric field obtained from the MD simulations in TIP3 water. The amide I and A frequencies are strongly positively correlated with the C=O and N-H bond lengths. The C=O and C-N amide bond lengths are negatively correlated, suggesting the solvent-induced fluctuations of the contribution of zwitterionic resonance form. Sampling the global electric field in the entire region of the transition charge densities (TCDs) is required for accurate infrared line shape simulations. Collective electrostatic solvent coordinates which represent the fluctuations of the 10 lowest amide fundamental and overtone states are reported. Normal-mode analysis of an NMA-3H(2)O cluster shows that the 660 cm(-1) to 1100 cm(-1) oscillation found in the frequency autocorrelation functions of the amide modes may be ascribed to the two bending vibrations of intermolecular hydrogen bonds with the amide oxygen of NMA.

Amides↗
PubMed2006

Anharmonicity of amide modes.

The principal contributions to the anharmonic coupling of amide vibrations are explored with the objective of comparing recent experiments with density functional theory and evaluating simple models of mode coupling. Experimental information obtained by means of two-dimensional infrared spectroscopy (2D IR) is reasonably well predicted by the computed one- and two-quantum anharmonic modes of amide-A, -I, and -II types in mono-, di- and tripeptides. The expansion of the vibrational energy up to the cubic and quartic coupling of harmonic modes suggested criteria to assess how localized are the forces determining the anharmonicity. The off-diagonal anharmonicity between an amide-A and one other amide mode was shown to be mainly determined by forces involving only these two modes, whereas the off-diagonal anharmonicity of two amide-I modes in peptides depended significantly on forces due to motions other than those of the amide-I type. Both the diagonal and off-diagonal anharmonicities exhibit sensitivity to peptide structures. These results should prove useful in linking 2D IR experimental results to secondary structure. Further, the results are used to evaluate the vibrational exciton model for the mixed-mode anharmonicities of the amide-I transitions.

Amides↗
PubMed2004

Preparation of beta- and gamma-lactams from carbamoyl radicals derived from oxime oxalate amides.

A general synthetic route to oxime oxalate amides was developed and applied to the preparation of molecules incorporating N-benzyl-N-alkenyl amides linked with acetone oxime or benzaldoxime units. In addition, 2-substituted-thiazolidine-4-carboxylic acid methyl ester amides of oxalyl benzaldoxime were also prepared. It was shown by EPR spectroscopy that the oxalyl benzaldoxime amides dissociated to produce benziminyl and carbamoyl (aminoacyl) radicals when photolysed with 4-methoxyacetophenone as a photosensitizer. Carbamoyl radicals derived from N-alk-3-enyl oxime oxalate amides underwent ring closure to afford pyrrolidin-2-ones. The analogous N-alk-2-enyl precursors afforded azetidin-2-ones. Reactions of the cyclohexenyl and cinnamyl oxime oxalate amides afforded a bicyclic beta-lactam and a 3-benzyl-substituted beta-lactam respectively. Interestingly, both products were isolated as hydroxylated compounds. A thiazolidine-derived oxime oxalate amide containing an isobutenyl side chain also dissociated with production of the corresponding thiazolidinyl-carbamoyl radical, as shown by EPR spectroscopy. GC-MS evidence indicated that this radical cyclised to afford some of the corresponding penicillin derivative

Amides↗
PubMed1991

Cleavage kinetics and anchor linked intermediates in solid phase peptide amide synthesis.

Kinetics and cleavage conditions of peptide amide synthesis were studied using the anchor molecules 5-(4'-aminomethyl-3',5'-dimethoxyphenoxy)valeric acid (4-ADPV-OH) and 5-(2'-aminomethyl-3'-5'-dimethoxyphenoxy) valeric acid (2-ADPV-OH). Unexpectedly the anchor amide alanyl-4-ADPV-NH2 was isolated and characterized as an intermediate during the cleavage with trifluoroacetic acid (TFA) of alanyl-4-ADPV-alanyl-aminomethyl-polystyrene to yield the alanine amide. As a matter of fact the NH--CH alpha bond of the alanyl spacer has to be cleaved to form this intermediate. Using TFA-dichloromethane (1:9) alanyl-4-ADPV-NH2 was obtained as a cleavage product in 50% yield within 60 min, whereas the isomeric alanyl-2-ADPV-NH2 was formed more slowly under these mild conditions. At high TFA concentration no difference between the 2- and 4-ADPV anchor was observed in the rate of formation of the free alanine amide. The presence of tryptophan amide in the cleavage mixture resulted in an anchor alkylated tryptophan amide, which remains stable in acidic solution but disappears rapidly in the presence of the resin. A low TFA/high TFA cleavage procedure is recommended for peptide amid synthesis applying the ADPV anchor.

Alkylation↗
PubMed1991

Biosynthesis of vitamin B12: stepwise amidation of carboxyl groups b, d, e, and g of cobyrinic acid a,c-diamide is catalyzed by one enzyme in Pseudomonas denitrificans.

The cobalamin biosynthetic pathway enzyme that catalyzes amidation of 5'-deoxy-5'-adenosyl-cobyrinic acid a,c-diamide was purified to homogeneity from extracts of a recombinant strain of Pseudomonas denitrificans by a four-column procedure. The purified protein had an isoelectric point of 5.6 and molecular weights of 97,300 as estimated by gel filtration and 57,000 as estimated by gel electrophoresis under denaturing conditions, suggesting that the active enzyme is a homodimer. Stepwise Edman degradation provided the sequence of the first 16 amino acid residues at the N terminus. The enzyme catalyzed the four-step amidation sequence from cobyrinic acid a,c-diamide to cobyric acid via the formation of cobyrinic acid triamide, tetraamide, and pentaamide intermediates. The amidations are carried out in a specific order; this order was not determined. The enzyme was specific to coenzyme forms of substrates and did not carry out amidation of the carboxyl group at position f. The amidation reactions were ATP/Mg2+ dependent and exhibited a broad optimum around pH 7.5. L-Glutamine was shown to be the preferred amide group donor (Km congruent to 45 microM) but could be replaced by ammonia (Km = 20 mM). For all of the four partially amidated substrates, the Km values were in the micromolar range and the Vmax values were about 7,000 nmol h-1 mg-1.

Amides↗
PubMed1985

Characterization of peptide alpha-amidation activity in human cerebrospinal fluid and central nervous system tissue.

Peptidyl-glycine alpha-amidation activity has been detected in human cerebrospinal fluid (CSF) and in several regions of the central nervous system. Activity was monitored by measuring conversion of mono-125I-D-Tyr-Val-Gly into mono-125I-D-Tyr-Val-NH2. The alpha-amidation activity in CSF is dependent on molecular oxygen, copper ions and ascorbic acid and appears to recognize a variety of peptide substrates which contain carboxyl terminal glycine residues. Kinetic analyses demonstrated Michaelis-Menten kinetics with a Km of 4.6 microM for D-Tyr-Val-Gly. The level of peptidyl-glycine alpha-amidation activity in 14 samples of CSF averaged 43 +/- 5 pmol/ml/h (mean +/- SEM; range 11-85 pmol/ml/h) or 1.9 +/- 0.2 pmol/Mg protein/h. No difference was noted between samples from male and female subjects. Extracts of central nervous system tissue contained alpha-amidation activity. The highest levels of enzyme activity were found in the hypothalamus with lower levels in the neurohypophysis and the cerebral cortex. Still lower but detectable activity was found in the cerebellum and pons. Human peptidyl-glycine alph-amidation activity is found in central nervous system tissues known to synthesize alpha-amidated neuropeptides and may be secreted from these tissues along with alpha-amidated peptides into CSF.

Amides↗
PubMed1992

Nematocidal activity of long alkyl chain amides, amines, and their derivatives on dog roundworm larvae.

The nematocidal activity of amides and amines having a long alkyl chain against the second-stage larva of dog roundworm, Toxocara canis, was examined. Long chain acyl amides with smaller substituents on the nitrogen showed stronger activity and the activity of cyclic amine amides was stronger than that of acyclic ones. In a series of homologous amides, the activity was dependent on the alkyl chain length: it reached a maximum at an optimal chain length and decreased in both shorter and longer homologues. The relationship between the activity and hydrophobicity of the homologues was analysed by the use of the bilinear model. The hydrophobicity of a compound, which gives a maximal activity, was similar for all neutral amides, but amides which have an additional amine group in the molecule had different values. Tertiary amines and their salts having a long alkyl chain also showed nematocidal activities comparable to those of the corresponding amides. The salts killed the larva at concentrations lower than their critical micell concentration, suggesting that they behave as a single molecule for the nematocidal action.

Amides↗
PubMed1994

Identification of the C-terminal amino acid amides by carboxypeptidase Y digestion and fast atom bombardment mass spectrometry.

The combination method of carboxypeptidase Y digestion and fast atom bombardment (FAB) mass spectrometry is described for the identification of C-terminal amino acid amides in peptides. Carboxypeptidase Y has amidase activity as well as exopeptidase activity in the same digestion buffer condition. Based on this concept, we develop a new technique which can definitively and easily identify the C-terminal amino acid amides. This method obviates the need for several complicated steps occurring in previous methods, but improves sensitivity, and enables exact identification of the amino acid amide by the difference of molecular mass. Analyses of carboxypeptidase Y digested peptides, not liberated free amino acid amides, were carried out by fast atom bombardment mass spectrometry. The use of truncated peptides by fast atom bombardment mass spectrometry in C-terminal amino acid amide determination gives several advantages over analyses of the liberated amino acid amides. The C-terminal amino acid amides of Allantostatin I (Leu-NH2), alpha-Melanocyte Stimulating Hormone (Val-NH2), and Ranatensin (Met-NH2) are unequivocally determined at a level of 0.90-2.3 nmol per peptide. This approach is based on entirely different principles than the previous approaches.

Amides↗
PubMed1998

Normalization of fasting glycaemia by intravenous GLP-1 ([7-36 amide] or [7-37]) in type 2 diabetic patients.

Intravenous GLP-1 [7-36 amide] can normalize fasting hyperglycaemia in Type 2 diabetic patients. Whether GLP-1 [7-37] has similar effects and how quickly plasma glucose concentrations revert to hyperglycaemia after stopping GLP-1 is not known. Therefore, 8 patients with Type 2 diabetes (5 female, 3 male; 65+/-6 years; BMI 34.3+/-7.9 kg m(-2); HbA1c 9.6+/-1.2%; treatment with diet alone (n=2), sulphonylurea (n=5), metformin (n=1)) were examined twice in randomized order. GLP-1 [7-36 amide] or [7-37] (1 pmol kg(-1)min(-1) were infused intravenously over 4 h in fasted subjects. Plasma glucose (glucose-oxidase), insulin and C-peptide (ELISA) was measured during infusion and for 4 h thereafter. Indirect calorimetry was performed. Fasting hyperglycaemia was 11.7+/-0.9 [7-36 amide] and 11.3+/-0.9 mmol l(-1) [7-37]. GLP-1 infusions stimulated insulin secretion approximately 3-fold (insulin peak 168+/-32 and 156+/-47 pmol l(-1), p<0.0001 vs basal; C-peptide peak 2.32+/-0.28 and 2.34+/-0.43 nmol l(-1), p<0.0001, respectively, with GLP-1 [7-36 amide] and [7-37]). Four hours of GLP-1 infusion reduced plasma glucose (4.8+/-0.4 and 4.6+/-0.3 mmol l(-1), p<0.0001 vs basal values), and it remained in the non-diabetic fasting range after a further 4 h (5.1+/-0.4 and 5.3+/-0.4 mmol l(-1), for GLP [7-36 amide] and [7-37], respectively). There were no significant differences between GLP-1 [7-36 amide] and [7-37] (glucose, p=0.99; insulin, p=0.99; C-peptide, p=0.99). Neither glucose oxidation nor lipid oxidation (or any other parameters determined by indirect calorimetry) changed during or after the administration of exogenous GLP-1. In conclusion, GLP-1 [7-36 amide] and [7-37] normalize fasting hyperglycaemia in Type 2 diabetic patients. Diabetes therapy (diet, sulphonyl ureas or metformin) does not appear to influence this effect. In fasting and resting patients, the effect persists during administration of GLP-1 and for at least 4 h thereafter, without rebound. Significant changes in circulating substrate concentrations (e.g. glucose) are not accompanied by changes in intracellular substrate metabolism.

Age of Onset↗
PubMed2000

The enzymatic formation of novel bile acid primary amides.

Bifunctional peptidylglycine alpha-amidating monooxygenase (PAM) catalyzes the copper-, ascorbate-, and O(2)-dependent cleavage of C-terminal glycine-extended peptides and N-acylglycines to the corresponding amides and glyoxylate. The alpha-amidated peptides and the long-chain acylamides are hormones in humans and other mammals. Bile acid glycine conjugates are also substrates for PAM leading to the formation of bile acid amides. The (V(MAX)/K(m))(app) values for the bile acid glycine conjugates are comparable to other known PAM substrates. The highest (V(MAX)/K(m))(app) value, 3.1 +/- 0.12 x 10(5) M(-1) s(-1) for 3-sulfolithocholylglycine, is 6.7-fold higher than that for d-Tyr-Val-Gly, a representative peptide substrate. The time course for O(2) consumption and glyoxylate production indicates that bile acid glycine conjugate amidation is a two-step reaction. The bile acid glycine conjugate is first converted to an N-bile acyl-alpha-hydroxyglycine intermediate which is ultimately dealkylated to the bile acid amide and glyoxylate. The enzymatically produced bile acid amides and the carbinolamide intermediates were characterized by mass spectrometry and two-dimensional (1)H-(13)C heteronuclear multiple quantum coherence NMR.

Bile Acids and Salts↗
PubMed1998

Glucagon-like peptide-1 (7-36) amide as a novel neuropeptide.

Although earlier studies indicated that GLP-1 (7-36) amide was an intestinal peptide with a potent effect on glucose-dependent insulin secretion, later on it was found that several biological effects of this peptide occur in the brain, rather than in peripheral tissues. Thus, proglucagon is expressed in pancreas, intestine, and brain, but post translational processing of the precursor yields different products in these organs, glucagon-like peptide-1 (7-36) amide being one of the forms produced in the brain. Also, GLP-1 receptor cDNA from human and rat brains has been cloned and sequenced, and the deduced amino acid sequences are the same as those found in pancreatic islets. Through these receptors, GLP-1 (7-36) amide from gut or brain sources induces its effects on the release of neurotransmitters from selective brain nuclei, the inhibition of gastric secretion and motility, the regulation of food and drink intake, thermoregulation, and arterial blood pressure. Central administration (icv) of GLP-1 (7-36) amide produces a marked reduction in food and water intake, and the colocalization of the GLP-1 receptor, GLUT-2, and glucokinase mRNAs in hypothalamic neurons involved in glucose sensing suggests that these cells may be involved in the transduction of signals needed to produce a state of fullness. In addition, GLP-1 (7-36) amide inhibits gastric acid secretion and gastric emptying, but these effects are not found in vagotomized subjects, suggesting a centrally mediated effect. Similar results have been found with the action of this peptide on arterial blood pressure and heart rate in rats. Synthesis of GLP-1 (7-36) amide and its own receptors in the brain together with its abovementioned central physiological effects imply that this peptide may be considered a neuropeptide. Also, the presence of GLP-1 (7-36) amide in the synaptosome fraction and its calcium-dependent release by potassium stimulation, suggest that the peptide may act as a neurotransmitter although further electrophysiological and ultrastructural studies are needed to confirm this possibility.

Animals↗
PubMed2000

New insights into copper monooxygenases and peptide amidation: structure, mechanism and function.

Many bioactive peptides must be amidated at their carboxy terminus to exhibit full activity. Surprisingly, the amides are not generated by a transamidation reaction. Instead, the hormones are synthesized from glycine-extended intermediates that are transformed into active amidated hormones by oxidative cleavage of the glycine N-C alpha bond. In higher organisms, this reaction is catalyzed by a single bifunctional enzyme, peptidylglycine alpha-amidating monooxygenase (PAM). The PAM gene encodes one polypeptide with two enzymes that catalyze the two sequential reactions required for amidation. Peptidylglycine alpha-hydroxylating monooxygenase (PHM; EC 1.14.17.3) catalyzes the stereospecific hydroxylation of the glycine alpha-carbon of all the peptidylglycine substrates. The second enzyme, peptidyl-alpha-hydroxyglycine alpha-amidating lyase (PAL; EC 4.3.2.5), generates alpha-amidated peptide product and glyoxylate. PHM contains two redox-active copper atoms that, after reduction by ascorbate, catalyze the reduction of molecular oxygen for the hydroxylation of glycine-extended substrates. The structure of the catalytic core of rat PHM at atomic resolution provides a framework for understanding the broad substrate specificity of PHM, identifying residues critical for PHM activity, and proposing mechanisms for the chemical and electron-transfer steps in catalysis. Since PHM is homologous in sequence and mechanism to dopamine beta-monooxygenase (DBM; EC 1.14.17.1), the enzyme that converts dopamine to norepinephrine during catecholamine biosynthesis, these structural and mechanistic insights are extended to DBM.

Amidine-Lyases↗
PubMed1990

Characterization of receptors for glucagon-like peptide-1(7-36)amide on rat lung membranes.

Specific binding of 125I-labelled GLP-1(7-36)amide to rat lung membranes was dependent upon time and temperature and was proportional to membrane protein concentration. Binding was inhibited in a concentration-dependent manner by unlabelled GLP-1(7-36)amide consistent with the presence of a single class of binding sites with a dissociation constant (Kd) of 1.67 +/- 0.29 nmol/l. GLP-1(1-36)amide was 260 times less potent in inhibiting the binding of 125I-labelled GLP-1(7-36)amide to lung membranes (Kd of 448 +/- 93 nmol/l). Vasoactive intestinal polypeptide and peptide-histidine-isoleucine also displaced 125I-labelled GLP-1(7-36)amide from the receptor concentration-dependently; the Kd was 4.31 +/- 0.8 and 7.93 +/- 4.79 nmol/l, respectively. Guanine nucleotides (GTP-gamma-S, GDP-beta-S) decreased the binding of 125I-labelled GLP-1(7-36)amide to rat lung membranes as was found for GLP-1(7-36)amide receptors in RINm5F cells which were also shown to be coupled to the adenylate cyclase system.

Adenylyl Cyclases↗
PubMed1995

Characterisation of the processing by human neutral endopeptidase 24.11 of GLP-1(7-36) amide and comparison of the substrate specificity of the enzyme for other glucagon-like peptides.

The post-secretory processing of the potent insulinotropic peptide hormone, GLP-1(7-36)amide, probably involves one or more of a small group of membrane-bound ectopeptidases. Reported here, is the characterisation of the endoproteolysis of human GLP-1(7-36)amide by the recombinant human form of neutral endopeptidase (NEP) 24.11, which is one of the best characterised and widely-distributed of ectopeptidases and is involved in the processing of other peptide hormones. The products of the limited endoproteolysis were characterised by mass and primary structure following fractionation using high performance liquid chromatography. The rate of this endoproteolysis by NEP 24.11 was estimated and compared to that of GLP-1(7-36)amide-related peptides. GLP-1(7-36)amide appears to be good substrate for NEP 24.11 with most, but not all potential target bonds being cleaved. Also, the structurally-related peptides, secretin and glucagon appear to be good substrates whereas GIP and exendin-4 are very poor substrates. That the GLP-1(7-36)amide super-agonist, exendin-4 is a poor substrate for NEP 24.11 is significant for the possible use of this peptide as a prototype for the development of clinically-useful peptide agonists. Further studies should reveal whether NEP 24.11 is important for the metabolic clearance of GLP-1(7-36)amide and will be highly relevant for the attempts to realise the suggested therapeutic value of GLP-1(7-36)amide.

Amino Acid Sequence↗
PubMed1996

Glucagon-like peptide-1(7-36)amide enhances insulin-stimulated glucose uptake and decreases intracellular cAMP content in isolated rat adipocytes.

We investigated the effect of GLPs on glucose uptake in isolated rat adipocytes. GLP-1(7-36)amide significantly enhanced glucose uptake in the presence of 1 nM insulin. GLP-1(7-36)amide at 15 nM increased glucose uptake maximally by 56.4% as compared with 1 nM insulin alone (P < 0.01). In contrast, with less than 1 nM insulin or without insulin GLP-1(7-36)amide showed no effect on glucose uptake. Full-sequence GLP-1(1-37) at 15 nM in the presence of 1 nM insulin increased glucose uptake by 24.6% as compared with 1 nM insulin alone (P < 0.05). GLP-2 showed no effect on glucose uptake. Further, we examined the effect of GLP-1(7-36)amide on cAMP content in isolated rat adipocytes. Insulin at 1 nM caused a significant decrease of cAMP content. The combination of 15 nM GLP-1(7-36)amide and 1 nM insulin caused a further reduction of cAMP content. These data indicate that GLP-1(7-36)amide possesses augmentative effects on insulin action in isolated rat adipocytes. Furthermore, it is suggested that the stimulatory effect of GLP-1(7-36)amide occurs through the reduction of intracellular cAMP content.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Comparison of peptidyl-glycine alpha-amidation activity in medullary thyroid carcinoma cells, pheochromocytomas, and serum.

With an assay based on the radioimmunological detection of the formation of the C-terminal amide function on a neuropeptide Y-like substrate, amidation enzyme activity with apparent Mr of 56,000 and 38,000 was found in pheochromocytoma extracts. The larger molecular form of amidating enzyme was also expressed and secreted from medullary thyroid carcinoma cells in a dexamethasone-suppressible way. Serum contained high levels of amidating enzyme activity with no difference between normal subjects and patients with pheochromocytomas. However, the majority of the amidating activity in serum was of much larger size, Mr between 80 and 105,000, compared to that released from the endocrine cells. No major difference was found between the molecular forms of amidation enzyme from tissues and from serum either in respect of enzyme kinetics or in respect of requirements for the cofactors copper and ascorbate. The major serum forms of enzyme were relatively independent of exogenous copper; however, they could still be quenched by cobber chelating agents. It is concluded that the molecular weight forms of the amidating enzyme circulating in serum are much larger than the soluble enzyme stored and secreted from most endocrine tissues.

Adrenal Gland Neoplasms↗
PubMed1993

Effects of glucagon like peptide-1(7-36) amide on the cytoplasmic Ca(2+)-concentration in rat islet cells.

Glucagon like peptide-1(7-36) amide (GLP-1(7-36)amide) stimulates both insulin secretion and the efflux of 45Ca2+ from 45Ca(2+)-preloaded rat islets in a Na(+)-dependent manner. This indicates that the peptide stimulates insulin secretion by Na(+)-dependently increasing the intracellular concentration of Ca2+ ([Ca2+]IC). However, whether GLP-1(7-36)amide actually affects the [Ca2+]IC in islet cells is not known. We therefore preloaded rat islet cells with the Ca(2+)-fluorophor fura 2-AM and examined the [Ca2+]IC in spectrophotofluorometry. We found that GLP-1(7-36)amide increased [Ca2+]IC both at 3.3 and 8.3 mM glucose but only in a medium containing both Ca2+ and Na+. Also the adenylate cyclase activator, forskolin (2.5 microM), increased the [Ca2+]IC but this action was evidenced also in the absence of extracellular Na+. Furthermore, the Ca(2+)-channel inhibitor, D-600 (50 microM), prevented the rise in [Ca2+]IC after both forskolin and GLP-1(7-36)amide, whereas pertussis toxin had no effect. The results show that GLP-1(7-36)amide increases the [Ca2+]IC in islets cells by an action that most likely is due to uptake of extracellular Ca2+ by a Na(+)-dependent mechanism, whereas forskolin increases [Ca2+]IC independently on Na+. It is hypothesized that GLP-1(7-36)amide stimulates a Na(+)-dependent step prior to the catalytic unit of the adenylate cyclase complex in islet cells.

Animals↗
PubMed1985

Actions of the molluscan neuropeptide FMRF-amide on neurones in the suboesophageal ganglia of the snail Helix aspersa.

The effects of the molluscan neuropeptide FMRF-amide were tested on several neurones in the suboesophageal ganglia of the snail Helix aspersa. Almost all neurones tested responded to the peptide, some being hyperpolarized (H response) and others depolarized (D response). The H response is due primarily to an inward potassium current and may be blocked in 20 microM 4-aminopyridine. The hyperpolarizing actions of FMRF-amide and dopamine may be separated by ergometrine which blocks the response to dopamine but not to FMRF-amide. The D response is due mainly to an inward sodium current but this is not blocked by d-tubocurarine, morphine or TTX. It appears to be mediated by a distinct receptor/ionophore as excitation by ACh and 5-HT are both antagonized by d-tubocurarine. The Leu2-substituted analogue FLRF-amide was found to produce similar H responses to FMRF-amide, but was much less potent at producing D responses. It did, however, produce cross-desensitization of the D response to FMRF-amide, suggesting that it does bind to the FMRF-amide receptor.

Animals↗