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PubMed1997

The global activator GacA of Pseudomonas aeruginosa PAO positively controls the production of the autoinducer N-butyryl-homoserine lactone and the formation of the virulence factors pyocyanin, cyanide, and lipase.

The global activator GacA, a highly conserved response regulator in Gram-negative bacteria, is required for the production of exoenzymes and secondary metabolites in Pseudomonas spp. The gacA gene of Pseudomonas aeruginosa PAO1 was isolated and its role in cell-density-dependent gene expression was characterized. Mutational inactivation of gacA resulted in delayed and reduced formation of the cell-density signal N-butyryl-L-homoserine lactone (BHL), of the cognate transcriptional activator RhIR (VsmR), and of the transcriptional activator LasR, which is known to positively regulate RhIR expression. Amplification of gacA on a multicopy plasmid caused precocious and enhanced production of BHL, RhIR and LasR. In parallel, the gacA gene dosage markedly influenced the BHL/RhIR-dependent formation of the cytotoxic compounds pyocyanin and cyanide and the exoenzyme lipase. However, the concentrations of another known cell-density signal of P. aeruginosa, N-oxododecanoyl-L-homoserine lactone, did not always match BHL concentrations. A model accounting for these observations places GacA function upstream of LasR and RhIR in the complex, cell-density-dependent signal-transduction pathway regulating several exoproducts and virulence factors of P. aeruginosa via BHL.

4-Butyrolactone↗

PubMed2003

Acyl-homoserine lactone acylase from Ralstonia strain XJ12B represents a novel and potent class of quorum-quenching enzymes.

N-acylhomoserine lactones (AHLs) are used as signal molecules by many quorum-sensing Proteobacteria. Diverse plant and animal pathogens use AHLs to regulate infection and virulence functions. These signals are subject to biological inactivation by AHL-lactonases and AHL-acylases. Previously, little was known about the molecular details underlying the latter mechanism. An AHL signal-inactivating bacterium, identified as a Ralstonia sp., was isolated from a mixed-species biofilm. The signal inactivation encoding gene from this organism, which we call aiiD, was cloned and successfully expressed in Escherichia coli and inactivated three AHLs tested. The predicted 794-amino-acid polypeptide was most similar to the aculeacin A acylase (AAC) from Actinoplanes utahensis and also shared significant similarities with cephalosporin acylases and other N-terminal (Ntn) hydrolases. However, the most similar homologues of AiiD are deduced proteins of undemonstrated function from available Ralstonia, Deinococcus and Pseudomonas genomes. LC-MS analyses demonstrated that AiiD hydrolyses the AHL amide, releasing homoserine lactone and the corresponding fatty acid. Expression of AiiD in Pseudomonas aeruginosa PAO1 quenched quorum sensing by this bacterium, decreasing its ability to swarm, produce elastase and pyocyanin and to paralyze nematodes. Thus, AHL-acylases have fundamental implications and hold biotechnological promise in quenching quorum sensing.

4-Butyrolactone↗

PubMed1999

Antinociception caused by the extract of Hedyosmum brasiliense and its active principle, the sesquiterpene lactone 13-hydroxy-8,9-dehydroshizukanolide.

The hydroalcoholic extract (HE) obtained from stems and leaves of Hedyosmum brasiliense, given i.p., produced significant inhibition of acetic acid-induced abdominal constriction in mice, with a mean ID50 of 12.7 mg/kg. This effect installed rapidly (0.5 h) and lasted for up to 2 h. Given orally up to 1000 mg/kg, the HE was ineffective. When assessed in the formalin response the HE, given i.p., inhibited the first and second phase, with ID50s of 31.1 and 21.7 mg/kg for the first and the second phases, respectively. The HE also inhibited capsaicin-induced neurogenic pain with ID50 of 69.0 mg/kg, but, in contrast to morphine, failed to cause analgesia in either the tail-flick or hot-plate models of pain. In addition, its antinociception was not reversed by naloxone. The sesquiterpene lactone 13-hydroxy-8,9-dehydroshizukanolide, isolated from H. brasiliense and already reported in other plant species (given by i.p., i.t., or i.c.v. routes) exhibited graded antinociception against acetic-acid writhing and capsaicin-induced licking. Additionally, we have corrected some physico-chemical data already reported for this compound. It is concluded that both the extract and the sesquiterpene lactone isolated from H. brasiliense produced marked antinociception in different models of chemical pain. The site of action involved in the antinociception of the 13-hydroxy-8,9-dehydroshizukanolide remains unclear, but the opioid pathway seems unlikely to be involved in its action.

Acetic Acid↗

PubMed2004

Isolation of a new 15-membered macrocyclic glycolipid lactone, Cuscutic Resinoside a from the seeds of Cuscuta chinensis: a stimulator of breast cancer cell proliferation.

While searching for new estrogenic compounds from the plant kingdom, we investigated an extract of the seeds of Cuscuta chinensis (Convolvulaceae) which showed potency for stimulating MCF-7 cell proliferation. A novel resin glycoside, cuscutic resinoside A ( 6) was isolated along with five known compounds from the extract. The structure was deduced from its spectral data as (11 S)-hydroxyhexadecanoic acid 11- O-alpha- L-(4- O-2 R,3 R-nilylrhamnopyranosyl)-(1-->2)- O-alpha- L-rhamnopyranosyl-(1,2-lactone) forming a unique 15-membered macrocyclic lactone. The compound significantly stimulated not only MCF-7 cell proliferation but also T47D human breast cancer cells at a concentration of 10 microM. Along with cuscutamine ( 1) and kaempferol ( 4), 6 was tested in the transient luciferase reporter assay and was found to have different luciferase inducing activity characteristics from the other compounds. These results suggest that 6 stimulated cancer cell proliferation by a different mechanism from 1 and 4.

Breast Neoplasms↗

PubMed2005

Modulation of the G2 cell cycle checkpoint by sesquiterpene lactones psilostachyins A and C isolated from the common ragweed Ambrosia artemisiifolia.

A phenotypic cell-based assay for inhibitors of the G (2) DNA damage checkpoint was used to screen plant extracts from the US National Cancer Institute Natural Products Repository. It revealed activity in a methanol extract from the common ragweed Ambrosia artemisiifolia. Assay-guided fractionation led to the identification of the sesquiterpene lactones psilostachyins A and C as novel checkpoint inhibitors. Elimination of their alpha,beta-unsaturated carbonyl group caused a loss of activity, suggesting that the compounds can bind covalently to target proteins through Michael addition. Psilostachyins A and C also blocked cells in mitosis and caused the formation of aberrant microtubule spindles. However, the compounds did not interfere with microtubule polymerization in vitro. The related sesquiterpene lactones psilostachyin B, paulitin and isopaulitin were also isolated from the same extract but showed no checkpoint inhibition. The identification of the target(s) of psilostachyins A and C may provide further insight into the signalling pathways involved in cell cycle arrest and mitotic progression.

Ambrosia↗

PubMed2004

Revisiting quorum sensing: Discovery of additional chemical and biological functions for 3-oxo-N-acylhomoserine lactones.

Bacteria use small diffusible molecules to exchange information in a process called quorum sensing. An important class of autoinducers used by Gram-negative bacteria is the family of N-acylhomoserine lactones. Here, we report the discovery of a previously undescribed nonenzymatically formed product from N-(3-oxododecanoyl)-L-homoserine lactone; both the N-acylhomoserine and its novel tetramic acid degradation product, 3-(1-hydroxydecylidene)-5-(2-hydroxyethyl)pyrrolidine-2,4-dione, are potent antibacterial agents. Bactericidal activity was observed against all tested Gram-positive bacterial strains, whereas no toxicity was seen against Gram-negative bacteria. We propose that Pseudomonas aeruginosa utilizes this tetramic acid as an interference strategy to preclude encroachment by competing bacteria. Additionally, we have discovered that this tetramic acid binds iron with comparable affinity to known bacterial siderophores, possibly providing an unrecognized mechanism for iron solubilization. These findings merit new attention such that other previously identified autoinducers be reevaluated for additional biological functions.

4-Butyrolactone↗

PubMed2005

The molecular structure and catalytic mechanism of a quorum-quenching N-acyl-L-homoserine lactone hydrolase.

In many Gram-negative bacteria, including a number of pathogens such as Pseudomonas aeruginosa and Erwinia carotovora, virulence factor production and biofilm formation are linked to the quorum-sensing systems that use diffusible N-acyl-L-homoserine lactones (AHLs) as intercellular messenger molecules. A number of organisms also contain genes coding for lactonases that hydrolyze AHLs into inactive products, thereby blocking the quorum-sensing systems. Consequently, these enzymes attract intense interest for the development of antiinfection therapies. However, the catalytic mechanism of AHL-lactonase is poorly understood and subject to controversy. We here report a 2.0-angstroms resolution structure of the AHL-lactonase from Bacillus thuringiensis and a 1.7-angstroms crystal structure of its complex with L-homoserine lactone. Despite limited sequence similarity, the enzyme shows remarkable structural similarities to glyoxalase II and RNase Z proteins, members of the metallo-beta-lactamase superfamily. We present experimental evidence that AHL-lactonase is a metalloenzyme containing two zinc ions involved in catalysis, and we propose a catalytic mechanism for bacterial metallo-AHL-lactonases.

Bacillus thuringiensis↗

PubMed2005

Three-dimensional structure of the quorum-quenching N-acyl homoserine lactone hydrolase from Bacillus thuringiensis.

The three-dimensional structure of the N-acyl-l-homoserine lactone hydrolase (AHL lactonase) from Bacillus thuringiensis has been determined, by using single-wavelength anomalous dispersion (SAD) phasing, to 1.6-angstroms resolution. AHLs are produced by many Gram-negative bacteria as signaling molecules used in quorum-sensing pathways that indirectly sense cell density and regulate communal behavior. Because of their importance in pathogenicity, quorum-sensing pathways have been suggested as potential targets for the development of novel therapeutics. Quorum-sensing can be disrupted by enzymes evolved to degrade these lactones, such as AHL lactonases. These enzymes are members of the metallo-beta-lactamase superfamily and contain two zinc ions in their active sites. The zinc ions are coordinated to a number of ligands, including a single oxygen of a bridging carboxylate and a bridging water/hydroxide ion, thought to be the nucleophile that hydrolyzes the AHLs to ring-opened products, which can no longer act as quorum signals.

Bacillus thuringiensis↗

PubMed2006

A structurally unrelated mimic of a Pseudomonas aeruginosa acyl-homoserine lactone quorum-sensing signal.

The pathogenic bacterium Pseudomonas aeruginosa uses acyl-homoserine lactone quorum-sensing signals to coordinate the expression of a battery of virulence genes in a cascade of regulatory events. The quorum-sensing signal that triggers the cascade is N-3-oxo-dodecanoyl homoserine lactone (3OC12-HSL), which interacts with two signal receptor-transcription factors, LasR and QscR. This signal is base labile, and it is degraded by mammalian PON lactonases. We have identified a structurally unrelated triphenyl mimic of 3OC12-HSL that is base-insensitive and PON-resistant. The triphenyl mimic seems to interact specifically with LasR but not with QscR. In silico analysis suggests that the mimic fits into the 3OC12-HSL-binding site of LasR and makes key contacts with LasR. The triphenyl mimic is an excellent scaffold for developing quorum-sensing inhibitors, and its stability and potency make it ideal for biotechnology uses such as heterologous gene expression.

4-Butyrolactone↗

PubMed1995

A second N-acylhomoserine lactone signal produced by Pseudomonas aeruginosa.

Quorum sensing systems are used by a number of Gram-negative bacterial species to regulate specific sets of genes in a cell density-dependent manner. Quorum sensing involves synthesis and detection of extracellular signals termed autoinducers. As shown in recombinant Escherichia coli, the Pseudomonas aeruginosa autoinducer (PAI) N-(3-oxododecanoyl)homoserine lactone, together with the lasR gene product, activate the P. aeruginosa lasB gene. In this study, PAI was shown to activate lasB-lacZ expression in a P. aeruginosa lasR mutant containing a plasmid with lasR under the control of the lac promoter. The concentration of PAI necessary for half-maximal activation of the lasB-lacZ fusion was approximately 1 microM, which is within the range of PAI levels found in P. aeruginosa culture fluids. The effect of PAI on a P. aeruginosa lasR mutant containing a plasmid with lasR under the control of its own promoter and containing the lasB-lacZ fusion was also tested. Although extracts of culture fluid activated the lasB promoter in this construct, concentrations of PAI as high as 10 microM did not. This indicates the presence of a second extracellular factor (factor 2) that is required for lasB activation in P. aeruginosa when lasR is controlled by its own promoter but not when lasR is controlled by a strong foreign promoter. Factor 2 was shown to be N-butyrylhomoserine lactone. Although recombinant E. coli cells containing the PAI synthase gene, lasI, produce PAI, these cells do not produce factor 2. Furthermore, a P. aeruginosa mutant that produced about 0.1% of the wild-type level of PAI made about 5% of the wild-type level of factor 2. This indicates that factor 2 synthesis results from the activity of a gene product other than PAI synthase. The role of factor 2 in virulence gene regulation remains to be determined, but this compound may affect the expression of lasR, which in turn activates transcription of numerous virulence genes in the presence of sufficient PAI. Apparently, multiple quorum sensing systems can occur and interact with each other in a single bacterial species.

4-Butyrolactone↗

PubMed2000

Acyl-homoserine lactone quorum sensing in gram-negative bacteria: a signaling mechanism involved in associations with higher organisms.

Recent advances in studies of bacterial gene expression have brought the realization that cell-to-cell communication and community behavior are critical for successful interactions with higher organisms. Species-specific cell-to-cell communication is involved in successful pathogenic or symbiotic interactions of a variety of bacteria with plant and animal hosts. One type of cell-cell signaling is acyl-homoserine lactone quorum sensing in Gram-negative bacteria. This type of quorum sensing represents a dedicated communication system that enables a given species to sense when it has reached a critical population density in a host, and to respond by activating expression of genes necessary for continued success in the host. Acyl-homoserine lactone signaling in the opportunistic animal and plant pathogen Pseudomonas aeruginosa is a model for the relationships among quorum sensing, pathogenesis, and community behavior. In the P. aeruginosa model, quorum sensing is required for normal biofilm maturation and for virulence. There are multiple quorum-sensing circuits that control the expression of dozens of specific genes that represent potential virulence loci.

4-Butyrolactone↗

PubMed2003

Interactions of a family 18 chitinase with the designed inhibitor HM508 and its degradation product, chitobiono-delta-lactone.

We describe enzymological and structural analyses of the interaction between the family 18 chitinase ChiB from Serratia marcescens and the designed inhibitor N,N'-diacetylchitobionoxime-N-phenylcarbamate (HM508). HM508 acts as a competitive inhibitor of this enzyme with a K(i) in the 50 microM range. Active site mutants of ChiB show K(i) values ranging from 1 to 200 microM, providing insight into some of the interactions that determine inhibitor affinity. Interestingly, the wild type enzyme slowly degrades HM508, but the inhibitor is essentially stable in the presence of the moderately active D142N mutant of ChiB. The crystal structure of the D142N-HM508 complex revealed that the two sugar moieties bind to the -2 and -1 subsites, whereas the phenyl group interacts with aromatic side chains that line the +1 and +2 subsites. Enzymatic degradation of HM508, as well as a Trp --> Ala mutation in the +2 subsite of ChiB, led to reduced affinity for the inhibitor, showing that interactions between the phenyl group and the enzyme contribute to binding. Interestingly, a complex of enzymatically degraded HM508 with the wild type enzyme showed a chitobiono-delta-lactone bound in the -2 and -1 subsites, despite the fact that the equilibrium between the lactone and the hydroxy acid forms in solution lies far toward the latter. This shows that the active site preferentially binds the (4)E conformation of the -1 sugar, which resembles the proposed transition state of the reaction.

Binding Sites↗

PubMed2006

Direct evidence for the modulation of the activity of the Erwinia chrysanthemi quorum-sensing regulator ExpR by acylhomoserine lactone pheromone.

In Erwinia chrysanthemi production of pectic enzymes is controlled by a complex network involving several regulators. Among them is ExpR, the quorum-sensing regulatory protein. ExpR is a member of the LuxR family of transcriptional regulators, the activity of which is modulated by the binding of diffusible N-acylhomoserine lactone pheromones to the N-terminal receptor site of the proteins. Previous in vitro DNA-ExpR binding studies suggested that ExpR might activate pectic enzyme production and repress its cognate gene expression. This report presents genetic evidence that ExpR represses its own gene expression in the absence of pheromone and that the addition of pheromone promotes concentration-dependent de-repression. In vitro experiments show that (i) ExpR binds target DNA in the absence of pheromone and that the pheromone dissociates ExpR-DNA complexes, (ii) ExpR binds target DNA in a non-cooperative fashion, and (iii) two molecules of pheromone are bound per molecule of ExpR dimer. In the absence of N-(3-oxo-hexanoyl)-homoserine lactone, ExpR prevents RNA polymerase access to the expR promoter, thereby directly repressing transcription initiation. The presence of pheromone renders the expR promoter accessible to RNA polymerase and results in the de-repression of transcription initiation. Overall we have established that there is a direct modulation of the repressive activity of a LuxR family regulator by a pheromone. Furthermore, site-directed mutagenesis experiments strongly suggest that the ExpR residues Leu-19, Tyr-31, and Ser-125 are involved in the transduction of conformational changes induced by ligand binding, and this provides new insights into the structure-function relationship of this bacterial regulator family.

4-Butyrolactone↗

PubMed2003

Production of acylated homoserine lactones by different serotypes of Vibrio anguillarum both in culture and during infection of rainbow trout.

Onehundred and forty-eight out of onehundred and fifty strains of Vibrio anguillarum isolated from vibriosis in Danish marine aquaculture produced bacterial communication signals, acylated homoserine lactones, eliciting a response in the Agrobacterium tumefaciens (pZLR4) monitoring system. One strain, a serotype O4, induced a strong response in the Chromobacterium violaceum (CV026) monitoring system. Profiles of AHLs determined by TLC separation revealed the presence of at least four AHLs and a compound similar to N-3-oxo-decanoyl homoserine lactone (3-oxo-C10-HSL) was present in all strains. The production rate of the presumed 3-oxo-C10-HSL followed the growth rate of V. anguillarum whereas the production rate of a small AHL (Rf value of 0.74) increased faster than the growth rate of V. anguillarum indicating autoinduction. AHLs were produced by all serotypes (O1 to O10) and by non-typable strains. During infection with V. anguillarum, AHLs could be extracted from liver, kidney and muscle of rainbow trout and AHLs were detected both in vitro and in vivo when cell numbers reached 10(7) per ml or gram. Preliminary investigations of interactions between AHLs and the fish immune system were carried out determining oxidative burst of fish macrophages exposed to 3-oxo-C10-HSL. No activation or suppression of the superoxide anion production in the head kidney macrophages was seen when treated with the AHL compound in concentrations of 1 nM-10 microM. Our data show that AHLs are produced by almost all V. anguillarum strains and that no clear pattern relating AHL production to disease or virulence appear.

4-Butyrolactone↗

PubMed2001

Resistance to macrocyclic lactone anthelmintics by Haemonchus contortus and Ostertagia circumcincta in sheep in New Zealand.

AIM: To establish the efficacy of oral formulations of ivermectin and moxidectin against naturally acquired abomasal nematode infections on a North Island sheep farm. METHODS: Two controlled slaughter trials were undertaken. In the first, 30 sheep on pasture were randomly allocated on the basis of faecal egg count to 1 of 3 groups, comprising an untreated control group and 2 treatment groups. One treatment group was given a single oral dose of ivermectin and the other a single oral dose of moxidectin, both at the manufacturer's recommended dose rates of 0.2 mg/kg liveweight. Six days after treatment, all animals were slaughtered and their abomasa recovered for worm counting. The second trial, which involved 47 animals, was essentially the same as the first except that, as well as involving the slaughter of 30 sheep from all 3 groups, 6 days after treatment, it also included a further 8 untreated control animals and 9 moxidectin treated animals which were slaughtered 27 days after treatment. RESULTS: At 6 days after treatment, moxidectin was highly effective against all 3 of the abomasal nematodes present. While ivermectin was similarly effective against Trichostrongylus axei 6 days after treatment, it was not effective against either Ostertagia circumcinta or Haemonchus contortus, against which average efficacies of only 63.6% and 61.6%, respectively, were recorded. At 27 days after treatment, moxidectin, was also highly effective against T. axei (97.3% reduction) but not against either H. contortus (71.4% reduction) or O. circumcinta (61.0% reduction). CONCLUSIONS: These results provide the first record of macrocyclic lactone resistance in H. contortus in sheep or in any other host in New Zealand, and the first case where such resistance has been exhibited in more than one parasite species at a time. Although the therapeutic efficacy of moxidectin was high against these resistant H. contortus and O. circumcincta strains, resistance to moxidectin was indicated by its diminished prophylactic activity against them. It is suggested that this reduction in the prophylactic activity of moxidectin is also likely to reduce its apparent current high therapeutic efficacy. CLINICAL RELEVANCE: As well as providing further evidence that it can no longer be automatically assumed that macrocylic lactone anthelmintics will be effective on sheep farms in this country, these findings also present a warning that increasingly complex parasite control options may have to be faced in the future.

Journal Article↗

PubMed2003

Probable multigeneric resistance to macrocyclic lactone anthelmintics in cattle in New Zealand.

AIM: To establish the efficacy of topical formulations of eprinomectin and abamectin against naturally acquired abomasal and small intestinal nematode infections in cattle purchased from a North Island bull-beef property. METHODS: A controlled slaughter trial, involving eighteen 6-8-month-old mixed breed calves, was conducted in May 2002.The animals were randomly allocated on the basis of faecal egg count to one of three equal-sized groups (n=6), consisting of an untreated control group and two treatment groups. One of the treatment groups was treated with a topical formulation of eprinomectin, the other with abamectin. Both anthelmintics were administered as a single topical treatment on an individual liveweight basis, at the manufacturer's recommended dose rates of 0.5 mg/kg. All calves were housed in separate groups with no access to pasture throughout the entire trial and were slaughtered 7-10 days after treatment. RESULTS: Both anthelmintic treatments were highly effective(worm count reduction >98%) against Ostertagia ostertagi, Trichostrongylus axei and Cooperia punctata, but were not effective at reducing worm counts significantly of either Cooperia oncophora or Trichostrongylus longispicularis. Against these latter two parasites, worm count reductions of only 72% and 79%, and 81% and 76%, respectively, were recorded following treatment with eprinomectin or abamectin, respectively (all p>0.05). CONCLUSIONS: These results demonstrate evidence of resistance to macrocyclic lactone anthelmintics by C. oncophora and probably T. longispicularis also. CLINICAL RELEVANCE: As well as perhaps providing the first record of resistance to any anthelmintic by T. longispicularis, the present findings may also represent the first case of resistance to macrocyclic lactone anthelmintics exhibited by more than one parasite species at a time in cattle in New Zealand.

Journal Article↗

PubMed1988

Role of glutathione in the toxicity of the sesquiterpene lactones hymenoxon and helenalin.

Hymenoxon and helenalin are toxic sesquiterpene lactones present in the toxic range plants Hymenoxys odorata and Helenium microcephalum. Helenalin (25 mg/kg) or hymenoxon (30 mg/kg) administered to immature male ICR mice caused a rapid decrease in hepatic glutathione levels and were lethally toxic to greater than 60% of the animals within 6 d. L-2-Oxothiazolidine 4-carboxylate (OTC), a compound that elevates cellular glutathione levels, administered to mice 6 or 12 h before either helenalin or hymenoxon protected against hepatic glutathione depletion and the lethal toxicity of these toxins. OTC administered at the same time as the sesquiterpene lactones was not protective, suggesting that the critical events against which glutathione is protective occur within the first 6 h. In primary rat hepatocyte cultures, hymenoxon and helenalin (4-16 microM) caused a rapid lethal injury as determined by the release of lactate dehydrogenase. Cotreatment of cultures with N-acetylcysteine at high concentrations (4 mM) afforded significant protection against lethal injury by both toxins. In contrast, BCNU, which inhibits glutathione reductase, or diethylmaleate, which depletes hepatocellular glutathione, potentiated the hepatotoxicity of helenalin and hymenoxon in monolayer rat hepatocytes. These studies suggest that the in vivo and in vitro toxicity of hymenoxon and helenalin is strongly dependent on hepatic glutathione levels, which hymenoxon and helenalin rapidly deplete at very low concentrations.

Acetylcysteine↗

PubMed2005

Exogenous supply of pantoyl lactone to excised leaves increases their pantothenate levels.

BACKGROUND AND AIMS: All plants synthesize pantothenate but its synthesis and regulation are not well understood. The aim of this work is to study the effect of exogenous supply of precursor compounds on pantothenate levels in leaves. METHODS: Precursor compounds were supplied in solution to excised leaves and the pantothenate content was measured using a microbial method. KEY RESULTS: Pantothenate levels in excised leaves of Limonium latifolium, tomato (Lycopersicon esculentum), bean (Phaseolus vulgaris) and grapefruit (Citrus x paradisi) were examined following an exogenous supply of the precursor compounds pantoyl lactone or beta-alanine. Significantly higher levels of extractable pantothenate were found when pantoyl lactone was supplied, but not when beta-alanine was supplied despite a measurable uptake of beta-alanine into the leaf. CONCLUSIONS: The results suggested that the pantoate supply may be rate-limiting or regulating pantothenate synthesis in leaves.

4-Butyrolactone↗