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Inactivation of the lys7 gene, encoding saccharopine reductase in Penicillium chrysogenum, leads to accumulation of the secondary metabolite precursors piperideine-6-carboxylic acid and pipecolic acid from alpha-aminoadipic acid.

Pipecolic acid serves as a precursor of the biosynthesis of the alkaloids slaframine and swainsonine (an antitumor agent) in some fungi. It is not known whether other fungi are able to synthesize pipecolic acid. Penicillium chrysogenum has a very active alpha-aminoadipic acid pathway that is used for the synthesis of this precursor of penicillin. The lys7 gene, encoding saccharopine reductase in P. chrysogenum, was target inactivated by the double-recombination method. Analysis of a disrupted strain (named P. chrysogenum SR1-) showed the presence of a mutant lys7 gene lacking about 1,000 bp in the 3'-end region. P. chrysogenum SR1- lacked saccharopine reductase activity, which was recovered after transformation of this mutant with the intact lys7 gene in an autonomously replicating plasmid. P. chrysogenum SR1- was a lysine auxotroph and accumulated piperideine-6-carboxylic acid. When mutant P. chrysogenum SR1- was grown with L-lysine as the sole nitrogen source and supplemented with DL-alpha-aminoadipic acid, a high level of pipecolic acid accumulated intracellularly. A comparison of strain SR1- with a lys2-defective mutant provided evidence showing that P. chrysogenum synthesizes pipecolic acid from alpha-aminoadipic acid and not from L-lysine catabolism.

2-Aminoadipic Acid↗

Potentiation of phenobarbital-induced anticonvulsant activity by pipecolic acid.

Pipecolic acid (PA) is an intermediate of lysine metabolism in the mammalian brain. Recent findings suggest a functional connection of PA as neuromodulator in GABAergic transmission. Since many drugs are postulated to produce their effects by interaction with the central GABA system, the influence of PA on the anticonvulsant activity of phenobarbital was examined. Pretreatment of mice with 50 mg . kg-1 of PA potentiated the suppressing effects of the barbiturate on electrically and chemically induced convulsions. However, there was no potentiation of the behavioral effects and hypothermia induced by phenobarbital. PA itself had no or only little effect on the convulsions, motor function and rectal temperature when given in i.p. doses up to 500 mg . kg-1. Intraventricular administration of 500 microgram of PA also did not suppress either type of convulsion, although it produced ptosis, hypotonia, sedation and hypothermia. The results are discussed in relation to GABA system.

Animals↗

Comparative study on the correlation of plasma gamma-aminobutyric acid and pipecolic acid with liver function in patients with liver cirrhosis.

gamma-Aminobutyric acid (GABA) is an inhibitory neurotransmitter, elevated in plasma of patients with liver cirrhosis. Pipecolic acid (PA), a metabolite of lysine, and known to be a GABA receptor agonist, is also seen high levels in the plasma. To clarify the relationship of GABA, PA and liver function, plasma GABA and PA in three groups of chronic liver diseases (compensated cirrhosis, decompensated cirrhosis and decompensated cirrhosis with hepatic encephalopathy, HE) were analyzed and their liver functions were compared. This analysis demonstrated that both plasma GABA and PA were higher in these patients than in normal subjects. Plasma PA, but not plasma GABA, was closely correlated with plasma ammonia concentration in each group. No correlation was noted between plasma GABA and PA in each group. Plasma pipecolic acid was significantly higher in patients with esophageal varices than in patients with no varices. These findings suggest that increased PA may reflect the degree of portal hypertension. Although both GABA and PA are increased in chronic liver disease, they may have a different origin and disappearance rate including metabolic mechanism.

Journal Article↗

Lysine biosynthesis in Rhodotorula glutinis: properties of pipecolic acid oxidase.

Pipecolic acid oxidase from Rhodotorula glutinis, which converts pipecolic acid to alpha-aminoadipic-delta-semialdehyde, an intermediate of the biosynthetic pathway of lysine, was purified 290-fold. The enzyme from the crude extract and purified preparation exhibited a molecular weight of approximately 43,000 and was composed of a single subunit. The purified enzyme was heat labile and exhibited a pH optimum of 8.5 and an apparent Km for L-pipecolic acid of 1.67 X 10(-3) M. L-Proline acted as a competitive inhibitor for the enzyme. The enzyme was inhibited by the sulfhydryl agents p-chloromercuribenzoate and mercuric chloride. The in vitro enzyme activity required oxygen and upon oxidation of pipecolic acid, oxygen was reduced to hydrogen peroxide.

Hot Temperature↗

Origin of D- and L-pipecolic acid in human physiological fluids: a study of the catabolic mechanism to pipecolic acid using the lysine loading test.

Pipecolic acid, a metabolite of lysine, is found in human physiological fluids. It is known that plasma pipecolic acid levels are elevated in patients with Zellweger syndrome, a genetic disorder, and chronic liver diseases. However, it is uncertain if this acid originates directly from food intake or from mammalian or intestinal bacterial enzyme metabolism. To characterize the relationship between plasma pipecolic acid and diet, we analyzed the contents of pipecolic acid in 17 edible plants and changes in plasma and urinary pipecolic acid levels following soybean juice ingestion by 4 healthy volunteers. Our study revealed that some of the plants contained high concentrations of total pipecolic acid, and a higher portion of L-isomer than D-isomer. Loading tests demonstrated that plasma levels and urinary excretion of D-isomer increased significantly 2 h after soybean juice ingestion. Plasma lysine levels showed a similar increase to that of D-isomer. These findings suggest that plasma pipecolic acid, particularly the D-isomer, originates mainly from the catabolism of dietary lysine by intestinal bacteria rather than by direct food intake and that D- and L-isomer may have different mechanisms of metabolism. Moreover, these findings may be important for clarifying the pathogenesis of peroxisomal disorders.

Chromatography, High Pressure Liquid↗

L-Pipecolic acid oxidase, a human enzyme essential for the degradation of L-pipecolic acid, is most similar to the monomeric sarcosine oxidases.

L-Pipecolic acid oxidase activity is deficient in patients with peroxisome biogenesis disorders (PBDs). Because its role, if any, in these disorders is unknown, we cloned the associated human gene and expressed its protein product. The cDNA was cloned with the use of a reverse genetics approach based on the amino acid sequence obtained from purified L-pipecolic acid oxidase from monkey. The complete cDNA, obtained by conventional library screening and 5' rapid amplification of cDNA ends, encompassed an open reading frame of 1170 bases, translating to a 390-residue protein. The translated protein terminated with the sequence AHL, a peroxisomal targeting signal 1. Indirect immunofluorescence studies showed that the protein product was expressed in human fibroblasts in a punctate pattern that co-localized with the peroxisomal enzyme catalase. A BLAST search with the amino acid sequence showed 31% identity and 53% similarity with Bacillus sp. NS-129 monomeric sarcosine oxidase, as well as similarity to all sarcosine oxidases and dehydrogenases. No similarity was found to the peroxisomal D-amino acid oxidases. The recombinant enzyme oxidized both L-pipecolic acid and sarcosine. However, PBD patients who lack the enzyme activity accumulate only L-pipecolic acid, suggesting that in humans in vivo, this enzyme is involved mainly in the degradation of L-pipecolic acid.

Amino Acid Sequence↗

Analysis of pipecolic acid in biological fluids using capillary gas chromatography with electron-capture detection and [2H11]pipecolic acid as internal standard.

A sensitive and accurate stable isotope dilution assay was developed for the measurement of pipecolic acid in body fluids using capillary gas chromatography with electron-capture detection. The method utilizes [2H11]pipecolic acid as the internal standard. Sample preparation consisted of derivatization in aqueous solution (pH 11.5) of the amine moiety with methyl chloroformate to the N-methylcarbamate, followed by acidic ethyl acetate extraction at pH less than or equal to 2 and further derivatization of the carboxyl moiety with pentafluorobenzyl bromide, the excess of which was removed by solid-phase extraction. Control values have been determined in the plasma of at-term infants, age greater than 1 week (n = 21, mean = 1.36 microM, range = 0.47-3.27 microM). The utility of the method was demonstrated by quantitating pipecolic acid in biological fluids derived from patients with peroxisomal disorders. The method was validated against an established electron-capture negative ion mass fragmentographic technique.

Body Fluids↗

Pipecolic acid biosynthesis in Rhizoctonia leguminicola. II. Saccharopine oxidase: a unique flavin enzyme involved in pipecolic acid biosynthesis.

The fungal parasite Rhizoctonia leguminicola produces two indolizidine alkaloids, slaframine and swainsonine, of physiological interest. These alkaloids are biosynthesized from pipecolic acid which in turn is derived from L-lysine in this fungus as shown in the accompanying paper (Wickwire, B.M., Harris, C.M., Harris, T.M., and Broquist, H.P. (1989) J. Biol. Chem. 265, 14742-14747): L-lysine----saccharopine----delta 1----piperideine-6- carboxylate----pipecolate. This paper concerns the discovery, purification, and properties of a flavoenzyme, termed saccharopine oxidase, which carries out the oxidative cleavage of saccharopine as follows: Saccharopine + O2----delta 1-piperidine-6-carboxylate + glutamate + H2O2 The enzyme was purified 2,000-fold to homogeneity (polyacrylamide gel electrophoresis) in 14% yield from R. leguminicola mycelia, and had a native molecular mass of about 45,000 daltons by gel filtration (fast protein liquid chromatography Superose). Evidence for the presence of a flavin in the enzyme was drawn from these considerations: (a) the enzyme, while oxidatively cleaving saccharopine, concomitantly reduces 2,6-dichlorophenolindophenol; (b) the purified enzyme has a fluorescence spectrum typical of flavins; and (c) the enzyme requires oxygen and produces hydrogen peroxide. Good correlation was shown with purified saccharopine oxidase between disappearance of saccharopine with the concomitant appearance of delta 1-piperideine-6-carboxylate plus glutamate. The enzyme has a pH optimum about 6 and a Km for saccharopine of 0.128 mM. The enzyme apparently exists in R. leguminicola to shunt saccharopine, a major lysine metabolite, into a secondary pathway of lysine metabolism leading to pipecolate and subsequently to slaframine and swainsonine.

Amino Acids↗

Biochemical studies in the cerebro-hepato-renal syndrome of Zellweger: a disturbance in the metabolism of pipecolic acid.

The metabolism of pipecolic acid ahs been studied in three patients suffering from the cerebro-hepato-renal syndrome of Zellweger. A marked pipecolic aciduria was observed in these patients and serum levels of pipecolic acid were also elevated. From in vivo studies evidence was obtained that a disturbance in the catabolic pathway of pipecolic acid was present in all patients. This conclusion was based on the delayed return of the serum pipecolic acid concentration to the fasting concentration after oral loading of the patients with DL-pipecolic acid. Moreover, no increase in the excretion of alpha-amino adipic acid was observed in the patients after loading, in contrast with the control subjects, who showed a marked increase in the excretion of this metabolite of pipecolic acid. Further evidence for the presence of a metabolic defect in the catabolism of pipecolic acid was obtained from the observation that patients excreted significantly higher amounts of pipecolic acid during the loading experiment.

Amino Acids↗

The human L-pipecolic acid oxidase is similar to bacterial monomeric sarcosine oxidases rather than D-amino acid oxidases.

L-Pipecolic acid oxidase activity is deficient in patients with peroxisome biogenesis disorders (PBDs). Because its role, if any, in these disorders is unknown, the authors cloned the human gene to order to further study its functions. BLAST search of the translated sequence showed greatest homology to Bacillus sp. NS-129 monomeric sarcosine oxidase. The purified enzyme could use either L-pipecolic acid or sarcosine as a substrate. No homology was found to the peroxisomal D-amino acid oxidases. A further comparison of L-pipecolic acid oxidase to the two D-amino acid oxidases in peroxisomes showed that the proteins differed in many ways. First, both D-amino acid oxidase and L-pipecolic acid oxidase showed no enzyme activity in liver from Zellweger syndrome patients; D-aspartate oxidase activity was unchanged from control levels. Although all were targeted to peroxisomes, their targeting signals differed. No L-pipecolic acid oxidase was found in brain or other tissues outside of liver and kidney. The D-amino acid oxidases were similarly and more widely distributed. Finally, although D-amino acid degradation is limited to peroxisomes in mammals, L-pipecolic acid can be oxidized in either mitochondria or peroxisomes, or both.

Bacillus↗

Conversion of pipecolic acid into lysine in Penicillium chrysogenum requires pipecolate oxidase and saccharopine reductase: characterization of the lys7 gene encoding saccharopine reductase.

Pipecolic acid is a component of several secondary metabolites in plants and fungi. This compound is useful as a precursor of nonribosomal peptides with novel pharmacological activities. In Penicillium chrysogenum pipecolic acid is converted into lysine and complements the lysine requirement of three different lysine auxotrophs with mutations in the lys1, lys2, or lys3 genes allowing a slow growth of these auxotrophs. We have isolated two P. chrysogenum mutants, named 7.2 and 10.25, that are unable to convert pipecolic acid into lysine. These mutants lacked, respectively, the pipecolate oxidase that converts pipecolic acid into piperideine-6-carboxylic acid and the saccharopine reductase that catalyzes the transformation of piperideine-6-carboxylic acid into saccharopine. The 10.25 mutant was unable to grow in Czapek medium supplemented with alpha-aminoadipic acid. A DNA fragment complementing the 10.25 mutation has been cloned; sequence analysis of the cloned gene (named lys7) revealed that it encoded a protein with high similarity to the saccharopine reductase from Neurospora crassa, Magnaporthe grisea, Saccharomyces cerevisiae, and Schizosaccharomyces pombe. Complementation of the 10.25 mutant with the cloned gene restored saccharopine reductase activity, confirming that lys7 encodes a functional saccharopine reductase. Our data suggest that in P. chrysogenum the conversion of pipecolic acid into lysine proceeds through the transformation of pipecolic acid into piperideine-6-carboxylic acid, saccharopine, and lysine by the consecutive action of pipecolate oxidase, saccharopine reductase, and saccharopine dehydrogenase.

Amino Acid Sequence↗

Inhibition of intrathecally administered picrotoxin- and bicuculline-induced convulsions in mice by pipecolic acid or GABA.

Pipecolic acid (PA) is an alicyclic amino acid and putative neurotransmitter which may modulate GABAergic transmission in the central nervous system. The present study was designed to investigate the anticonvulsant effect of intrathecally (i.t.) injected PA on picrotoxin- and bicuculline-induced convulsions which are thought to be produced by interactions with GABAergic systems. Intrathecal injections of picrotoxin and bicuculline in mice produced convulsions which were characterized by a rapid onset and short duration. Coadministration of GABA with either bicuculline or picrotoxin, but not strychnine, attenuated the severity of the convulsions. Coadministration of PA also protected against bicuculline- and picrotoxin-induced convulsions. Intrathecal injections of PA produced a dose-related increase in the latency to the onset of these convulsions as well as a decrease in their duration, however PA failed to inhibit the duration of strychnine-induced seizures. The D isomer of PA was found to be more effective than the L isomer as an anticonvulsant in this study. When administered in a high dose (500 micrograms i.t.), the D isomer produced flaccid paralysis while injection of high doses (100-500 micrograms i.t.) of the L isomer actually elicited convulsions. These results further support an interaction between PA and GABAergic activity.

Animals↗

The lysine-ketoglutarate reductase-saccharopine dehydrogenase is involved in the osmo-induced synthesis of pipecolic acid in rapeseed leaf tissues.

Higher plant responses to abiotic stresses are associated with physiological and biochemical changes triggering a number of metabolic adjustments. We focused on L-lysine catabolism, and have previously demonstrated that degradation of this amino acid is osmo-regulated at the level of lysine-ketoglutarate reductase (LKR, EC 1.5.1.8) and saccharopine dehydrogenase (SDH, EC 1.5.1.9) in Brassica napus. LKR and SDH activities are enhanced by decreasing osmotic potential and decrease when the upshock osmotic treatment is followed by a downshock osmotic one. Moreover we have shown that the B. napus LKR/SDH gene is up-regulated in osmotically-stressed tissues. The LKR/SDH activity produces alpha-aminoadipate semialdehyde which could be further converted into alpha-aminoadipate and acetyl CoA. Alternatively alpha-aminoadipate could behave as a precursor for pipecolic acid. Pipecolic acid is described as an osmoprotectant in bacteria and is co-accumulated with proline in halophytic plants. We suggest that osmo-induction of the LKR/SDH activity could be partly responsible for pipecolic acid accumulation. This proposal has been assessed in this study through pipecolic acid amounts determination in rape leaf discs subjected to various upshift and downshift osmotic treatments. Changes in pipecolic acid level actually behave as those observed for LKR and SDH activities, since it increases or decreases in rape leaf discs treated under hyper- or hypo-osmotic conditions, respectively. In addition we show that pipecolic acid level is positively correlated with the external osmotic potential as well as with the duration of the applied treatment. On the other hand pipecolic acid level is related to the availability of L-lysine and not to that of D-lysine. Collectively the results obtained demonstrate that lysine catabolism through LKR/SDH activity is involved in osmo-induced synthesis of pipecolic acid.

Acetyl Coenzyme A↗

Pipecolic acid induces apoptosis in neuronal cells.

Pipecolic acid, a lysine metabolite, is thought to be a factor responsible for hepatic encephalopathy; however, the underlying mechanism is far from understood. Twenty minutes treatment with D-, L-, and DL-pipecolic acid at concentrations ranging from 1 to 100 microM, except for 1 microM L-pipecolic acid, had no inhibitory effect on excitatory postsynaptic responses in the dentate gyrus of rat hippocampal slices. In a whole-cell voltage-clamp configuration, DL-pipecolic acid (10 and 100 microM) did not affect voltage-sensitive Na(+) channel currents and K(+) channel currents, but it potentiated voltage-sensitive Ca(2+) channel currents, but to a lesser extent, in cultured rat cortical neurons and Neuro-2A cells, a mouse neuroblastoma cell line. Notably, 72-h treatment with D-, L-, and DL-pipecolic acid reduced Neuro-2A cell viability in a dose-dependent manner at concentrations ranging from 1 to 100 microM in a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, in parallel with reactions to propidium iodide, a marker of cell death, and Hoechst 33,342, a marker of apoptosis in a fluorescent microscopic study, with DL-pipecolic acid being the most potent. The results of the present study suggest that pipecolic acid could cause hepatic encephalopathy by inducing neuronal cell death, perhaps apoptosis, rather than by depressing neurotransmissions.

Animals↗

L-pipecolic acid metabolism in human liver: detection of L-pipecolate oxidase and identification of its reaction product.

L-Pipecolate oxidase, an enzyme that oxidizes L-pipecolic acid in the human liver has been demonstrated in the peroxisomal preparation. This enzyme oxidizes L-pipecolic acid with concomitant production of H2O2 in the peroxisome of the normal human liver. The immediate product of L-pipecolic acid oxidation has been identified as L-alpha-aminoadipate delta-semialdehyde. This reaction product was directly, and also after conversion to pipecolic acid by NaBH4 reduction, characterized by use of an amino acid analyzer and thin-layer chromatography. The pit fall of an indirect assay of L-pipecolate oxidase by means of the assay of alpha-aminoadipic acid formation was discussed.

2-Aminoadipic Acid↗

Determination of D- and L-pipecolic acid in food samples including processed foods.

BACKGROUND: Pipecolic acid, a metabolite of lysine, is found in human physiological fluids and is thought to play an important role in the central inhibitory gamma-aminobutyric acid system. However, it is unclear whether plasma D- and L-pipecolic acid originate from oral food intake or intestinal bacterial metabolites. METHODS: We analyzed the contents of D- and L-pipecolic acid in several processed foods including dairy products (cow's milk, cheese and yogurt), fermented beverages (beer and wine) and heated samples (beef, bovine liver, bread and tofu) to clarify the relationship between plasma D- and L-pipecolic acid and dietary foods. RESULTS: Our study revealed that some of the samples contained high concentrations of total pipecolic acid, and a higher proportion of L- than D-isomers. The other samples also showed high proportions of L-pipecolic acid. It was also shown that there is no significant change in the ratio of the D-isomer before and after heat treatment. The heat treatments could not cause the racemization of pipecolic acid in this study. CONCLUSION: These findings suggest that plasma pipecolic acid, particularly the D-isomer, does not originate from direct food intake and that D- and L-pipecolic acid can possibly be derived from intestinal bacterial metabolites.

Alcoholic Beverages↗