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PubMed1983

Purification and Characterization of a New Indole Oxygenase from the Leaves of Tecoma stans L.

A new indole oxygenase from the leaves of Tecoma stans was isolated and purified to homogenity. The purified enzyme system catalyzes the conversion of indole to anthranilic acid. It is optimally active at pH 5.2 and 30 degrees C. Two moles of oxygen are consumed and one mole of anthranilic acid is formed for every mole of indole oxidized. Dialysis resulted in complete loss of the activity. The inactive enzyme could be reactivated by the addition of concentrated dialysate. The enzyme is not inhibited by copper-specific chelators, non-heme iron chelators or atebrin. It is not a cuproflavoprotein, unlike the other indole oxygenases and oxidases.

Journal Article↗
PubMed2005

N-terminal anthranoyl-phenylalanine derivatives as CCK1 receptor antagonists: the final approach.

Starting from our lead compound, VL-0395, an anthranilic acid based CCK1 receptor antagonist, and following the well established "step by step" lead investigation strategy, we describe the final step of the anthranilic acid N-terminal optimization. Improvements for both affinity and selectivity towards CCK1 receptors have been accomplished through introduction of the fluoro substituent at C-5 and C-7 position of the indole ring together with the appropriate configuration of the aminoacidic chiral center.

Animals↗
PubMed1990

Involvement of Azospirillum brasilense plasmid DNA in the production of indole acetic acid.

Indole acetic acid (IAA) production in Azospirillum brasilense strain Sp245 is controlled by a 85 MDa plasmid naturally present in this bacterium. In the presence of L-tryptophan, anthranilic acid production and almost no IAA production occurs in a derivative strain harbouring a Tn5-Mob insertion in the 85 MDa plasmid. Agrobacterium tumefaciens strain GM19023, upon transfer of Tn5-Mob labelled 85 MDa plasmid of A. brasilense Sp245, gains the ability to produce anthranilic acid.

Azospirillum brasilense↗
PubMed1962

Tryptophanase-tryptophan synthetase systems in Escherichia coli. I. Effect of tryptophan and related compounds.

Freundlich, Martin (University of Minnesota, Minneapolis) and Herman C. Lichstein. Tryptophanase-tryptophan synthetase systems in Escherichia coli. I. Effect of tryptophan and related compounds. J. Bacteriol. 84:979-987. 1962.-The effect of tryptophan and related compounds on tryptophanase and tryptophan synthetase formation in Escherichia coli was determined. Several of these compounds stimulated the formation of tryptophanase while concomitantly decreasing the production of synthetase. A number of tryptophan analogues were found to inhibit growth. The possible mode of action of these substances was examined further. 5-Hydroxytryptophan greatly inhibited the formation of synthetase and also reduced growth. Its inhibitory action on growth was attributed, at least partially, to the false feedback inhibition of anthranilic acid formation. Tryptamine was found to be a potent inhibitor of the activity of synthetase, as well as of the enzyme(s) involved in the synthesis of anthranilic acid from shikimic acid. However, growth reduction was only partially reversed by tryptophan. Indole-3-acetic acid and indole-3-propionic acid decreased growth and increased the formation of synthetase six- to eightfold. The action of these compounds was ascribed to their ability to block the endogenous formation of tryptophan.

Escherichia coli↗
PubMed2005

Treatment of autoimmune neuroinflammation with a synthetic tryptophan metabolite.

Local catabolism of the amino acid tryptophan (Trp) by indoleamine 2,3-dioxygenase (IDO) is considered an important mechanism of regulating T cell immunity. We show that IDO transcription was increased when myelin-specific T cells were stimulated with tolerogenic altered self-peptides. Catabolites of Trp suppressed proliferation of myelin-specific T cells and inhibited production of proinflammatory T helper-1 (T(H)1) cytokines. N-(3,4,-Dimethoxycinnamoyl) anthranilic acid (3,4-DAA), an orally active synthetic derivative of the Trp metabolite anthranilic acid, reversed paralysis in mice with experimental autoimmune encephalomyelitis, a model of multiple sclerosis (MS). Trp catabolites and their derivatives offer a new strategy for treating T(H)1-mediated autoimmune diseases such as MS.

Adoptive Transfer↗
PubMed1989

Characteristics of interferon induced tryptophan metabolism in human cells in vitro.

Interferon-gamma-induced tryptophan metabolism of human macrophages was compared to ten human neoplastic cell lines of various tissue origin and to normal dermal human fibroblasts. Tryptophan and metabolites were determined in supernatants of cultures, after incubation for 48 h, by high-performance liquid chromatography with ultraviolet and fluorescence detection. With the exception of two cell lines (Hep G 2, hepatoma and CaCo 2, colon adenocarcinoma) in all of the ten other cells and cell lines tryptophan degradation was induced by interferon-gamma. Five of these ten formed only kynurenine (SK-N-SH, neuroblastoma; T 24, J 82, bladder carcinoma; A 431, epidermoid carcinoma; normal dermal fibroblasts), three formed kynurenine and anthranilic acid (U 138 MG, glioblastoma; SK-HEP-1, hepatoma; A 549, lung carcinoma). Only one line, A 498 (kidney carcinoma) showed the same pattern of metabolites as macrophages (kynurenine, anthranilic acid and 3-hydroxyanthranilic acid). Interferon-gamma regulated only the activity of indoleamine 2,3-dioxygenase. All other enzyme activities detected were independent of interferon-gamma, as shown by the capacity of the cells to metabolize L-kynurenine or N-formyl-L-kynurenine. Increasing the extracellular L-tryptophan concentration resulted in a marked induction of tryptophan degradation by macrophages. Contrarily, a significant decrease of the tryptophan degrading activity was observed when the extracellular L-tryptophan concentration was increased 2-fold with SK-N-SH, T 24 and J 82, 4-fold with A 431 and A 549 and 10-fold with U 138 MG and SK-HEP-1. The activity was unaffected by extracellular L-tryptophan with dermal fibroblasts and A 498. Though interferon-gamma was the most potent inducer of tryptophan metabolism, interferon-alpha and/or -beta showed small but distinct action on some of the cells. In all cells which reacted to interferon-gamma by enhanced expression of class I and/or class II major histocompatibility complex antigens tryptophan degradation was also inducible. These results demonstrate that induction of indoleamine 2,3-dioxygenase is a common feature of interferon-gamma action, that the extent of this induction is influenced by extracellular L-tryptophan concentrations and that indoleamine 2,3-dioxygenase is the only enzyme in the formation of 3-hydroxyanthranilic acid from tryptophan which is regulated by interferon-gamma.

Cell Line↗
PubMed2001

Biosynthesis of 2-aminobenzaldehyde in flowers of Robinia pseudoacacia and Philadelphus coronarius.

Feeding experiments with 13C- and fluorine-labelled precursors were performed to reveal the biosynthesis of 2-aminobenzaldehyde in flowers of Robinia pseudoacacia and Philadelphus coronarius. The results are in agreement with the transformation of anthranilic acid to indole followed by oxidative ring opening and hydrolysis of the resulting N-formyl-2-aminobenzaldehyde. This route differs from that observed in Hebeloma sacchariolens (Basidiomycetes) in which anthranilic acid is directly reduced to 2-aminobenzaldehyde.

Asteraceae↗
PubMed1989

Assays of three carcinogen/non-carcinogen chemical pairs for in vivo induction of chromosome aberrations, sister chromatid exchanges and micronuclei.

Three pairs of structurally similar carcinogenic/non-carcinogenic chemicals were tested for in vivo genotoxic activity in B6C3F1 mice. The carcinogenic/non-carcinogenic pairs, respectively, were o-toluidine hydrochloride/o-anthranilic acid, 4-chloro-o-phenylenediamine/4-nitro-o-phenylenediamine, and 3-(chloromethyl)pyridine hydrochloride/2-(chloromethyl)pyridine hydrochloride. Bone marrow cells from mice given intraperitoneal injections of up to the maximum tolerated dose were evaluated for chromosomal aberration, sister chromatid exchange, and micronucleus induction, o-anthranilic acid and o-toluidine hydrochloride did not increase the frequency of chromosomal aberrations or micronuclei. o-Toluidine hydrochloride increased the frequency of sister chromatid exchanges in two successive trials, while o-anthranilic acid had a positive effect on sister chromatid exchanges in two of three trials. Both 2-(chloromethyl) and 3-(chloromethyl)pyridine hydrochloride were negative for all three endpoints. Assays for chromosomal aberrations and micronuclei each distinguished between 4-chloro-o-phenylenediamine and its non-carcinogenic companion, 4-nitro-o-phenylenediamine. In the aberration test, 4-chloro-o-phenylenediamine produced a few cells with very large numbers of aberrations rather than an even distribution of damage among cells.

Animals↗
PubMed1985

Influence of dose and sex on the disposition and hepatic effects of cinnamyl anthranilate in the B6C3F1 mouse.

Cinnamyl anthranilate is a synthetic food flavouring and fragrance agent, formerly used at very low levels. There is currently some concern over the potential risk to man from its use, since it has been found to cause liver tumours in mice, following the administration of very large doses. This paper reports studies of its disposition and hepatic effects in B6C3F1 mice in relation to dose. Following a single oral dose of 500 mg cinnamyl anthranilate/kg body weight to B6C3F1 mice peak plasma levels of unchanged compound were reached in 30 min, and were higher in males than in females. Unchanged cinnamyl anthranilate in the urine accounted for 0.3-0.4% of the dose. Anthranilic acid (c. 17%) and hippuric acid (35%; the major metabolite of cinnamyl alcohol) were present in the urine, and recoveries of both were higher in females. Groups of male and female B6C3F1 mice were given 0, 10, 100, 1000, 5000, 15,000 and 30,000 ppm cinnamyl anthranilate in the diet. After 4 days, the diet was removed and urine collected for 24 hr. This contained cinnamyl anthranilate (more in males) hippuric and anthranilic acids (more in females) in concentrations that increased with dose. Other animals were given these diets for 19 days and then killed. Relative liver weight and hepatic microsomal cytochrome P-450 increased with increasing dose above 1000 ppm cinnamyl anthranilate, more markedly in males than in females although the maximum response (roughly twofold) was very similar in the two sexes. SDS-PAGE examination of the microsomes revealed the induction of a cytochrome P-450 isozyme of 53.1 kDa, but the aniline hydroxylase and p-nitroanisole O-demethylase activities of the 9000 g supernatant of liver were not induced. The data are discussed in terms of their significance for the human safety evaluation of cinnamyl anthranilate. It is important to note that liver hypertrophy, microsomal enzyme induction and the excretion of unchanged cinnamyl anthranilate all have the same dose-threshold for their appearance. This suggests that the hepatic effects of cinnamyl anthranilate may be mediated by unhydrolysed cinnamyl anthranilate, which is present only at very high doses due to the saturation of its hydrolysis.

Animals↗
PubMed1999

UV-Guided isolation of verrucines A and B, novel quinazolines from penicillium verrucosum structurally related to anacine from penicilliumaurantiogriseum

Two novel quinazolines, verrucines A (1) and B (2), have been isolated as a major and a minor metabolite, respectively, of Penicillium verrucosum. Both are condensates of one mole each of anthranilic acid, phenylalanine, and glutamine. The structures were elucidated by spectroscopic methods, and the two compounds were found to be epimers. The spectroscopic data for the ostensible benzodiazepine anacine reported from Penicillium aurantiogriseum, composed of one mole each of anthranilic acid, leucine, and glutamine, appeared very similar to those of 1. Therefore, a revised quinazoline structure for anacine is proposed.

Journal Article↗
PubMed2004

Photocatalytic actions of the pesticide metabolite 2-hydroxyquinoxaline: destruction of antioxidant vitamins and biogenic amines - implications of organic redox cycling.

Toxicity of the pesticide quinalphos may comprise secondary, delayed effects by its main metabolite 2-hydroxyquinoxaline (HQO). We demonstrate that HQO can destroy photocatalytically vitamins C and E, catecholamines, serotonin, melatonin, the melatonin metabolite AMK (N(1)-acetyl-5-methoxykynuramine), and unsubstituted and substituted anthranilic acids when exposed to visible light. In order to avoid HQO-independent ascorbate oxidation by light and to exclude actions by hydroxyl radicals, experiments on this vitamin were carried out in ethanolic solutions. Other substances tested (vitamin E, melatonin, anthranilic acids) were also photocatalytically destroyed by HQO in ethanol. After product analyses had indicated that HQO was not, or only poorly, degraded in the light, despite its catalytic action on other compounds, we followed directly the time course of HQO and ascorbate concentrations in ethanol. While ascorbate was largely destroyed, no change in HQO was demonstrable within 2 h of incubation. Destruction was not prevented by the singlet oxygen quencher DABCO. Obviously, HQO is capable of undergoing a process of organic redox cycling, perhaps via an intermediate quinoxaline-2-oxyl radical. Health problems from HQO intoxication may not only arise from the loss of valuable biomolecules, such as antioxidant vitamins and biogenic amines, but also from the formation of potentially toxic products. Dimerization and oligomerization are involved in several oxidation processes catalyzed by HQO, especially in the indoleamines, in dopamine, and presumably also in vitamin E. Melatonin oxidation by HQO did not only lead to the well-known - and usually protective - metabolite AFMK (N(1)-acetyl-N(2)-formyl-5-methoxykynuramine), but also to a high number of additional products, among them dimers and trimers. DABCO did not prevent melatonin destruction, but changed the spectrum of products. Serotonin was preferentially converted to a dimer, which can further oligomerize. Several indole dimers are known to be highly neurotoxic, as well as oxidation products formed from catecholamines via the adrenochrome/noradrenochrome pathway. Destruction of melatonin may cause deficiencies in circadian physiology, in immune functions and in antioxidative protection.

Amines↗
PubMed1991

Evaluation of the newborn mouse model for chemical tumorigenesis.

A total of 45 chemicals, including two aromatic hydrocarbons, five aromatic amines, three azo dyes, ten nitroso compounds, three steroids, four tryptophan metabolites and their related compounds, four naturally occurring substances, four pyrolysates of amino acids and ten miscellaneous compounds, were tested for newborn mouse tumorigenesis assay (NMTA). The results of the NMTA were compared with data from 'Survey of Compounds Which Have Been Tested for Carcinogenic Activity', NIH, NCI, USA (SCWHBTCA), and also with data from the IARC Monographs (Vols 1-41), Lyon, France (IARC). Of the 45 chemicals tested by the NMTA, 28 chemicals showed positive results in the NMTA, and the remaining 17 chemicals were found to be negative for tumor development. The correlation of the results between the NMTA and the mouse and/or rat carcinogenesis test starting at young adult age reported in the SCWHBTCA and in the IARC were compared with 37 chemicals tested; the remaining eight chemicals were found only in our NMTA results. It can be concluded that 31 out of 37 chemicals (83.8%) tested by the NMTA showed similar carcinogenic or non-carcinogenic results obtained in either adult mouse and/or rat carcinogenesis tests. The remaining six chemicals showed contradictory results between the NMTA and either adult mouse and/or rat carcinogenesis tests. Those six chemicals were N-hydroxy-4-acetylaminobiphenyl, estradiol, 3-hydroxyanthranilic acid, 3-hydroxy-L-kynurenine, isonicotinic acid hydrazide and phenobarbital. Among the 37 chemicals, 34 were comparable with the results of the adult mouse carcinogenesis test and those of the NMTA. Twenty-nine out of 34 chemicals (85.3%) showed similar results to the adult mouse carcinogenesis test. Contradictory results were obtained with the following five chemicals: N-hydroxy-acetylaminobiphenyl, 3-hydroxy-anthranilic acid, 3-hydroxy-L-kynurenine, isonicotinic acid hydrazide and phenobarbital. There were 35 chemicals which were comparable with the results of the adult rat carcinogenesis test, and 32 chemicals showed the same results as the NMTA (91.4%). Dissimilar results were obtained with the following three chemicals: estradiol, 3-hydroxy-anthranilic acid and phenobarbital. Based on the results presented in this report, it is reasonable to conclude that the NMTA is one of the most useful and reliable methods for detecting tumorigenic or non-tumorigenic chemicals, when a small amount of chemical is available for rodent carcinogenesis test and the duration of the study is limited to 1 year.

Animals↗
PubMed2001

The relative catalytic efficiency of beta-lactamase catalyzed acyl and phosphyl transfer.

Phosphonamidates which bear a simple resemblance to penicillin type structures have been synthesised as potential inhibitors of beta-lactamases: -ethyl N-(benzyloxycarbonyl) amidomethyl phosphonyl amides, PhCH(2)OCONHCH(2)P(O)(OEt)NR(2), the amines HNR(2) being l-proline, d-proline, l-thiazolidine, and o-anthranilic acid. The proline derivatives completely and irreversibly inactivated the class C beta-lactamase from Enterobacter cloacae P99, in a time-dependent manner, indicative of covalent inhibition. The inactivation was found to be exclusive to the class C enzyme and no significant inhibition was observed with any other class of beta-lactamase. The anthranilic acid derivative exhibited no appreciable inactivation of the beta-lactamases. The phosphonyl proline and phosphonyl thioproline derivatives were separated into their diastereoisomers and their individual second order rate constants for inhibition were found to be 7.72 +/- 0.37 and 8.3 x 10(-2) +/- 0.004 M(-1) s(-1) for the l-proline derivatives, at pH 7.0. The products of the inhibition reaction of each individual diastereoisomer, analyzed by electrospray mass spectroscopy, indicate that the more reactive diastereoisomers phosphonylate the enzyme by P-N bond fission with the elimination of proline. Conversely, gas chromatographic detection of ethanol release by the less reactive proline diastereoisomer suggests phosphonylation occurs by P-O bond fission. The enzyme enhances the rate of phosphonylation with P-N fission by at least 10(6) compared with that effected by hydroxide-ion. The pH dependence of the rate of inhibition of the beta-lactamase by the more reactive diasteroisomer is consistent with the reaction of the diprotonated form of the enzyme, EH(2), with the inhibitor, I (or its kinetic equivalents EH with IH). This pH dependence and the rate enhancement indicate that the enzyme appears to use the same catalytic apparatus for phosphonylation as that used for hydrolysis of beta-lactams. The stereochemical consequences of nucleophilic displacement at the phosphonyl centre are discussed.

Acylation↗
PubMed2001

Changes in kynurenic, anthranilic, and quinolinic acid concentrations in rat brain tissue during development.

Kynurenic, anthranilic, and quinolinic acid, brain tissue concentrations and indoleamine 2,3-dioxygenase [EC 1 13.11.17] activity were determined in rat brain, during pre- and postnatal development. Quinolinic acid brain tissue concentration was significantly increased at birth as compared with the prenatal level, then it declined rapidly in the postnatal period. By the contrary, kynurenic and anthranilic acids brain tissue concentrations in rat brain were significantly lower at birth as compared with those found prenatally; then kynurenic acid concentration decreased in the first postnatal week and increased thereafter, while anthranilic acid concentration increased in the first postnatal week and decreased thereafter. Indoleamine 2,3-dioxygenase [EC 1 13.11.17] activity were found unchanged in pre and post natal rat brain. The described opposite changes in quinolinic and kynurenic acids concentrations, occurring in pre- and postnatal period, despite the lack of knowledge on the precise role played by these compounds on the different neurotransmitter systems in the brain, could be involved in brain ontogenetic development.

Aging↗
PubMed2005

Processive action of cellobiohydrolase Cel7A from Trichoderma reesei is revealed as 'burst' kinetics on fluorescent polymeric model substrates.

Reaction conditions for the reducing-end-specific derivatization of cellulose substrates with the fluorogenic compound, anthranilic acid, have been established. Hydrolysis of fluorescence-labelled celluloses by cellobiohydrolase Cel7A from Trichoderma reesei was consistent with the active-site titration kinetics (burst kinetics), which allowed the quantification of the processivity of the enzyme. The processivity values of 88+/-10, 42+/-10 and 34+/-2.0 cellobiose units were found for Cel7A acting on labelled bacterial cellulose, bacterial microcrystalline cellulose and endoglucanase-pretreated bacterial cellulose respectively. The anthranilic acid derivatization also provides an alternative means for estimating the average degree of polymerization of cellulose and, furthermore, allows the quantitative monitoring of the production of reducing end groups on solid cellulose on hydrolysis by cellulases. Hydrolysis of bacterial cellulose by cellulases from T. reesei revealed that, by contrast with endoglucanase Cel5A, neither cellobiohydrolases Cel7A nor Cel6A produced detectable amounts of new reducing end groups on residual cellulose.

Binding Sites↗
PubMed1975

Tryptophan biosynthesis in Salmonella typhimurium: location in trpB of a genetic difference between strains LT2 and LT7.

Salmonella typhimurium prototrophs carrying a trpR mutation synthesize tryptophan biosynthetic enzymes constitutively. When feedback inhibition of anthranilate synthetase but not 5'-phosphoribosylpyrophosphate phosphoribosyltransferase activity was by-passed by growing cells on media supplemented with anthranilic acid, all trpR prototrophs overproduced and excreted tryptophan. However, the rate of tryptophan production depended on both the ancestry of the trpR strain and the integrity of its trpA gene. Prototrophs with trp genes derived from S. typhimurium strain LT2 produced tryptophan more efficiently than those with trp genes derived from strain LT7. This strain difference was cryptic insofar as it did not affect the growth rate; it was revealed only as a rate-limiting step in the constitutive biosynthesis of tryptophan in the presence of anthranilic acid, and was due to a lesion in the LT7-derived trpB gene. Strains with LT7-derived trp genes bearing a deletion in trpA produced tryptophan as readily as LT2 trpR prototrophs. This indicated that LT7-specific 5-phosphoribosylpyrophosphate phosphoribosyltransferase must be aggregated with the trpA gene produce to give an observable reduction of constitutive tryptophan production. The discovery of this strain difference has particular implications for studies involving the activities of trpA and B genes and their products in S. typhimurium and may have general significance for other studies involving different strains of Salmonella.

Anthranilate Synthase↗
PubMed1997

Tryptanthrins: a novel class of agonists of the aryl hydrocarbon receptor.

2,3,7,8-Tetrachlorodibenzo-p-dioxin and related environmental pollutants exert most of their adverse effects such as immunosuppression, induction of endocrine dysfunction, tumor promotion, and teratogenicity via the aryl hydrocarbon or dioxin receptor. While most potent agonists of the aryl hydrocarbon receptor are of synthetic origin, an increasing number of natural compounds are now recognized as receptor agonists. Our findings demonstrated that some tryptanthrin derivatives biosynthesized in incubations of Candida lipolytica with tryptophan and anthranilic acid or its derivatives were agonists of the aryl hydrocarbon receptor. The biosynthetic products 8-methyltryptanthrin, 8-chlorotryptanthrin, and 8-bromotryptanthrin induced cytochrome P4501A1 mRNA and protein in rat hepatocytes in primary culture, characteristic features of aryl hydrocarbon receptor agonists. Log-probit analysis of the catalytic activity of cytochrome P4501A1, 7-ethoxyresorufin O-deethylase (EROD), revealed EC50 induction values of 1.7, 0.25, and 0.17 microM for 8-methyltryptanthrin, 8-chlorotryptanthrin, and 8-bromotryptanthrin, respectively. Interestingly, the nonsubstituted tryptanthrin molecule, biosynthesized from the common physiological precursors tryptophan and anthranilic acid, was also active as an inducer. The specificity of the inducing effect of tryptanthrins was demonstrated in gel retardation experiments in Hepa-1 mouse hepatoma cells, showing the characteristic interaction of the activated aryl hydrocarbon receptor with an oligonucleotide containing a xenobiotic-responsive element. It is suggested that the receptor may be part of a defense system protecting higher organisms from secondary metabolites formed by the microflora of the host or its environment.

Animals↗
PubMed1999

Effects of Delphinium alkaloids on neuromuscular transmission.

The Delphinium alkaloids methyllycaconitine (MLA), nudicauline, 14-deacetylnudicauline (14-DN), barbinine, and deltaline were investigated for their effects on neuromuscular transmission in lizards. The substituent at C14 provides the only structural difference among the alkaloids MLA, nudicauline, 14-DN, and barbinine. Deltaline lacks the N-(methylsuccinyl)anthranilic acid at C18 common to the other four alkaloids. Each alkaloid reversibly reduced extracellularly recorded compound muscle action potential (CMAP) amplitudes in a concentration-dependent manner. The IC(50) values for CMAP blockade were between 0.32 and 13.2 microM for the N-(methylsuccinimido)anthranoyllycacotonine-type alkaloids and varied with the C14 moiety; the IC(50) value for deltaline was 156 microM. The slopes of the concentration-response curves for CMAP blockade were similar for each alkaloid except barbinine, whose shallower curve suggested alternative or additional mechanisms of action. Each alkaloid reversibly reduced intracellularly recorded spontaneous, miniature end-plate potential (MEPP) amplitudes. Alkaloid concentrations producing similar reductions in MEPP amplitude were 0.05 microM for 14-DN, 0.10 microM for MLA, 0.50 microM for barbinine, and 20 microM for deltaline. Only barbinine altered the time constant for MEPP decay, further suggesting additional or alternative effects for this alkaloid. MLA and 14-DN blocked muscle contractions induced by exogenously added acetylcholine. All five alkaloids are likely nicotinic receptor antagonists that reduce synaptic efficacy and block neuromuscular transmission. The substituent at C14 determines the potency and possibly the mechanism of nicotinic acetylcholine receptor blockade for MLA, nudicauline, 14-DN, and barbinine at neuromuscular synapses. The lower potency of deltaline indicates that the N-(methylsuccinyl)anthranilic acid at C18 affects alkaloid interactions with nicotinic acetylcholine receptors at neuromuscular junctions.

Acetylcholine↗