Dictyopterin, 6-(D-threo-1,2-dihydroxypropyl)-pterin, a new natural isomer of L-biopterin. Isolation from vegetative cells of Dictyostelium discoideum and identification

Microbial (Enzymatic) Degradation of Cyanide to Produce Pterins as Cofactors

Cyanide is one of the most poisonous substances in the environment, which may have originated from natural and anthropogenic sources. There are many enzymes produced by microorganisms which can degrade and utilize cyanide. The major byproducts of cyanide degradation are alanine, glutamic acid, alpha-amino-butyric acid, beta-cyanoalanine, pterin etc. These products have many pharmaceutical and medicinal applications. For the degradation of cyanide, microbes produce necessary cofactors which catalyze the degradation pathways. Pterin is one of the cofactors for cyanide degradation. There are many pathways involved for the degradation of cyanide, cyanate, and thiocyanate. Some of the microorganisms possess resistance to cyanide, since they have developed adaptive alternative pathways for the production of ATP by utilization of cyanide as carbon and nitrogen sources. In this review, we summarized different enzymes, their mechanisms, and corresponding pathways for the degradation of cyanide and production of pterins during cyanide degradation. We aim to enlighten different types of pterin, its classification, and biological significance through this literature review.

Dictyostelium: A Model for Studying the Extracellular Vesicle Messengers Involved in Human Health and Disease

Cell-derived extracellular vesicles (EVs) are newly uncovered messengers for intercellular communication. They are released by almost all cell types in the three kingdoms, Archeabacteria, Bacteria and Eukaryotes. They are known to mediate important biological functions and to be increasingly involved in cell physiology and in many human diseases, especially in oncology. The aim of this review is to recapitulate the current knowledge about EVs and to summarize our pioneering work about Dictyostelium discoideum EVs. However, many challenges remain unsolved in the EV research field, before any EV application for theranostics (diagnosis, prognosis, and therapy) of human cancers, can be efficiently implemented in the clinics. Dictyostelium might be an outstanding eukaryotic cell model for deciphering the utmost challenging problem of EV heterogeneity, and for unraveling the still mostly unknown mechanisms of their specific functions as mediators of intercellular communication.

Natural Products from Social Amoebae

Natural products are invaluable sources of structural diversity and complexity ideally suited for the development of therapeutic agents. The search for novel bioactive molecules has prompted scientists to explore various ecological niches. Microorganisms have been shown to constitute such an important source. Despite their biosynthetic potential, social amoebae, that is, microorganisms with both a uni- and multicellular lifestyle, are underexplored regarding their secreted secondary metabolome. In this review, we present the structural diversity of amoebal natural products and discuss their biological functions as well as their total syntheses.

Investigation of a potential role for aldose reductase AlrA in tetrahydropteridine synthesis in Dictyostelium discoideum Ax2

Dictyostelium discoideum Ax2 is well-known for the synthesis of d-threo-tetrahydrobiopterin (DH4) with a smaller amount of l-erythro-tetrahydrobiopterin (BH4). DH4 synthesis from 6-pyruvoyltetrahydropterin (PPH4) is catalyzed by aldose reductase (AR)-like protein and sepiapterin reductase (SR) via an intermediate 1′-oxo-2′-d-hydroxypropyl tetrahydropterin, which is non-enzymatically oxidized to d-sepiapterin in the absence of SR. However, l-sepiapterin was a dominant product in the reaction of a cellular extract of spr− disrupted in the SR gene. In order to investigate its potential role in tetrahydropteridine synthesis, the enzyme catalyzing l-sepiapterin synthesis from PPH4 was purified from spr −. Via mass spectrometry, the protein was identified to be encoded by alrA. AlrA consists of 297 amino acid residues sharing a high sequence identity with human AR. However, in the co-incubation assay, DH4 synthesis was not detected and, furthermore, the recombinant AlrA was observed to suppress BH4 synthesis by SR, which was known to prefer 1′-oxo-2′-d-hydroxypropyl tetrahydropterin to PPH4. Although intracellular DH4 level in alrA − was decreased to 60% of the wild type, it is presumed to result from the antioxidant function of DH4. Therefore, despite the structural and catalytic identities with human AR, AlrA seems to be involved in neither BH4, nor DH4 synthesis under normal physiological conditions.

Characterization of unexplored amidohydrolase enzyme-pterin deaminase

Pterin deaminase is an amidohydrolase enzyme hydrolyzing pteridines to form lumazine derivatives and ammonia. The enzyme captured the attention of scientists as early as 1959 and had been patented for its application as an anticancer agent. It is ubiquitously present in prokaryotes and has been reported in some eukaryotes such as honey bee, silkworm and rats. The enzyme has been observed to have a spectrum of substrates with the formation of respective lumazines. The role of the substrates of the enzyme in various metabolic pathways warrants a significant role in the biological activity of both prokaryotes and eukaryotes. Even though the functions of the enzyme have been explored in prokaryotes, their niche in the eukaryotic system is not clear. There is very few information on the structural and functional properties of the enzyme. This review has been congregated to emphasize the significance of pterin deaminase and analyzes the lacunae in understanding the biological characters of the enzyme.

Microcystbiopterins A-E, five O-methylated biopterin glycosides from two Microcystis spp. bloom biomasses

Five previously undescribed biopterin glycosides, microcystbiopterin A-E, were isolated from the extracts of two bloom materials of Microcystis spp. collected from a fishpond (IL-337) and Lake Kinneret (IL-347), Israel. The structure of the pterins was established by interpretation of their UV, CD, 1D and 2D NMR spectra and HR mass measurements. Microcystbiopterin D is the first heptose containing pterin glycoside to be reported in the literature. Their antimicrobial and cytotoxic properties were evaluated but all were found not active in both assays.

Lysosomes appear as the auto-fluorescent vacuoles in Dictyostelium discoideum cells

Dictyostelium discoideum cells contain auto-fluorescent vacuoles. To determine the identity of these vacuoles, the fluorescent dye 4-nitro-7-(1-piperazinyl)-2,1,3-benzoxadiazole (NBD-PZ) was used to stain the lysosomes in D. discoideum cells. Neither the auto-fluorescent vacuoles nor lysosomes were observed in D. discoideum cells immediately after they arose from spores or in stationary phase cells. However, both the auto-fluorescent vacuoles and lysosomes were visible in cells that had entered growth phase. Auto-fluorescent vacuoles and lysosomes were also observed in stationary phase cells incubated with chloroquine. When the cells were allowed to phagocytose BioParticles Fluorescent Bacteria (orange fluorescence) for 1 h, orange phagosomes and blue auto-fluorescent vacuoles were observed as independent moieties. However, after an additional 2 h of incubation, we observed vacuoles with mixed fluorescence (orange and blue) in the cells, suggestive of secondary lysosomes. These results suggest that the auto-fluorescent vacuoles in D. discoideum cells are lysosomes.

The Physarum polycephalum Genome Reveals Extensive Use of Prokaryotic Two-Component and Metazoan-Type Tyrosine Kinase Signaling

Physarum polycephalum is a well-studied microbial eukaryote with unique experimental attributes relative to other experimental model organisms. It has a sophisticated life cycle with several distinct stages including amoebal, flagellated, and plasmodial cells. It is unusual in switching between open and closed mitosis according to specific life-cycle stages. Here we present the analysis of the genome of this enigmatic and important model organism and compare it with closely related species. The genome is littered with simple and complex repeats and the coding regions are frequently interrupted by introns with a mean size of 100 bases. Complemented with extensive transcriptome data, we define approximately 31,000 gene loci, providing unexpected insights into early eukaryote evolution. We describe extensive use of histidine kinase-based two-component systems and tyrosine kinase signaling, the presence of bacterial and plant type photoreceptors (phytochromes, cryptochrome, and phototropin) and of plant-type pentatricopeptide repeat proteins, as well as metabolic pathways, and a cell cycle control system typically found in more complex eukaryotes. Our analysis characterizes P. polycephalum as a prototypical eukaryote with features attributed to the last common ancestor of Amorphea, that is, the Amoebozoa and Opisthokonts. Specifically, the presence of tyrosine kinases in Acanthamoeba and Physarum as representatives of two distantly related subdivisions of Amoebozoa argues against the later emergence of tyrosine kinase signaling in the opisthokont lineage and also against the acquisition by horizontal gene transfer.

Tetrahydropteridines possess antioxidant roles to guard against glucose-induced oxidative stress in Dictyostelium discoideum

Glucose effects on the vegetative growth of Dictyostelium discoideum Ax2 were studied by examining oxidative stress and tetrahydropteridine synthesis in cells cultured with different concentrations (0.5X, 7.7 g L^-1; 1X, 15.4 g L^-1; 2X, 30.8 g L^-1) of glucose. The growth rate was optimal in 1X cells (cells grown in 1X glucose) but was impaired drastically in 2X cells, below the level of 0.5X cells. There were glucose-dependent increases in reactive oxygen species (ROS) levels and mitochondrial dysfunction in parallel with the mRNA copy numbers of the enzymes catalyzing tetrahydropteridine synthesis and regeneration. On the other hand, both the specific activities of the enzymes and tetrahydropteridine levels in 2X cells were lower than those in 1X cells, but were higher than those in 0.5X cells. Given the antioxidant function of tetrahydropteridines and both the beneficial and harmful effects of ROS, the results suggest glucose-induced oxidative stress in Dictyostelium, a process that might originate from aerobic glycolysis, as well as a protective role of tetrahydropteridines against this stress. [BMB Reports 2013; 46(2): 86-91]

Tetrahydrobiopterin is functionally distinguishable from tetrahydrodictyopterin in Dictyostelium discoideum Ax2

Dictyostelium discoideum Ax2 produces both L-erythro-tetrahydrobiopterin (BH4) and its stereoisomer D-threo-BH4 (DH4). The putative cofactor function of them for phenylalanine hydroxylase (PAH) was investigated through genetic manipulation and quantitative determination of pteridines. In addition to establishing that dihydropteridine reductase (DHPR) and dihydrofolate reductase (DHFR) constitute the regeneration pathway of both BH4 and DH4, the results suggested that BH4 is a preferential cofactor for PAH in vivo, not a secondary product of DH4, which functions mainly as an antioxidant. Our result also demonstrated that PAH may be essential for Dictyostelium growth in nature, and thus it appears that the organism has evolved a strategy to maintain BH4 level via regeneration pathway at the expense of DH4 under oxidative stress conditions.

Structural insights into the dual substrate specificities of mammalian and Dictyostelium dihydropteridine reductases toward two stereoisomers of quinonoid dihydrobiopterin

Up to now, d-threo-tetrahydrobiopterin (DH(4), dictyopterin) was detected only in Dictyostelium discoideum, while the isomer L-erythro-tetrahydrobioterin (BH(4)) is common in mammals. To elucidate the mechanism of DH(4) regeneration by D. discoideum dihydropteridine reductase (DicDHPR), we have determined the crystal structure of DicDHPR complexed with NAD(+) at 2.16 Å resolution. Significant structural differences from mammalian DHPRs are found around the coenzyme binding site, resulting in a higher K(m) value for NADH (K(m)=46.51±0.4 μM) than mammals. In addition, we have found that rat DHPR as well as DicDHPR could bind to both substrates quinonoid-BH(2) and quinonoid-DH(2) by docking calculations and have confirmed their catalytic activity by in vitro assay.

Purification, crystallization and crystallographic analysis of Dictyostelium discoideum phenylalanine hydroxylase in complex with dihydrobiopterin and FeIII

Dictyostelium discoideum phenylalanine hydroxylase (DicPAH; residues 1-415) was expressed in Escherichia coli and purified for structural analysis. Apo DicPAH and DicPAH complexed with dihydrobiopterin (BH(2)) and Fe(III) were crystallized using 0.06 M PIPES pH 7.0, 26%(w/v) PEG 2000 by the hanging-drop vapour-diffusion method. Crystals of apo DicPAH and the DicPAH-BH(2)-Fe(III) complex diffracted to 2.6 and 2.07 A resolution, respectively, and belonged to space group P2(1), with unit-cell parameters a = 70.02, b = 85.43, c = 74.86 A, beta = 110.12 degrees and a = 70.97, b = 85.33, c = 74.89 A, beta = 110.23 degrees , respectively. There were two molecules in the asymmetric unit. The structure of DicPAH has been solved by molecular replacement.

Physarum nitric oxide synthases: genomic structures and enzymology of recombinant proteins

Physarum polycephalum expresses two closely related, calcium-independent NOSs (nitric oxide synthases). In our previous work, we showed that both NOSs are induced during starvation and apparently play a functional role in sporulation. In the present study, we characterized the genomic structures of both Physarum NOSs, expressed both enzymes recombinantly in bacteria and characterized their biochemical properties. Whereas the overall genomic organization of Physarum NOS genes is comparable with various animal NOSs, none of the exon-intron boundaries are conserved. Recombinant expression of clones with various N-termini identified N-terminal amino acids essential for enzyme activity, but not required for haem binding or dimerization, and suggests the usage of non-AUG start codons for Physarum NOSs. Biochemical characterization of the two Physarum isoenzymes revealed different affinities for L-arginine, FMN and 6R-5,6,7,8-tetrahydro-L-biopterin.

Structure of Chlorobium tepidum sepiapterin reductase complex reveals the novel substrate binding mode for stereospecific production of L-threo-tetrahydrobiopterin

Sepiapterin reductase (SR) is involved in the last step of tetrahydrobiopterin (BH(4)) biosynthesis by reducing the di-keto group of 6-pyruvoyl tetrahydropterin. Chlorobium tepidum SR (cSR) generates a distinct BH(4) product, L-threo-BH(4) (6R-(1'S,2'S)-5,6,7,8-BH(4)), whereas animal enzymes produce L-erythro-BH(4) (6R-(1'R,2'S)-5,6,7,8-BH(4)) although it has high amino acid sequence similarities to the other animal enzymes. To elucidate the structural basis for the different reaction stereospecificities, we have determined the three-dimensional structures of cSR alone and complexed with NADP and sepiapterin at 2.1 and 1.7 A resolution, respectively. The overall folding of the cSR, the binding site for the cofactor NADP(H), and the positions of active site residues were quite similar to the mouse and the human SR. However, significant differences were found in the substrate binding region of the cSR. In comparison to the mouse SR complex, the sepiapterin in the cSR is rotated about 180 degrees around the active site and bound between two aromatic side chains of Trp-196 and Phe-99 so that its pterin ring is shifted to the opposite side, but its side chain position is not changed. The swiveled sepiapterin binding results in the conversion of the side chain configuration, exposing the opposite face for hydride transfer from NADPH. The different sepiapterin binding mode within the conserved catalytic architecture presents a novel strategy of switching the reaction stereospecificities in the same protein fold.

D-threo-tetrahydrobiopterin is synthesized via 1'-oxo-2'-D-hydroxypropyl-tetrahydropterin in Dictyostelium discoideum Ax2

The biosynthesis of D-threo-tetrahydrobiopterin (DH4, tetrahydrodictyopterin) in Dictyostelium discoideum Ax2 was investigated through the mutant disrupted in the gene encoding sepiapterin reductase (SR) by insertional inactivation. The mutant cells, being completely devoid of SR protein, showed 18.1% of L-erythro-tetrahydrobiopterin (BH4) and 0.6% of DH4 productions in the wild type cells. The mutant cells were also identified to excrete D- and L-sepiapterin, which were presumed to originate from intracellular 1'-oxo-2'-D-hydroxypropyl- and 1'-oxo-2'-L-hydroxypropyl-tetrahydropterin (H4-pterin), respectively. Furthermore, in a coupled assay with Dictyostelium SR, the mutant cell extract exhibited a novel enzyme activity converting 6-pyruvoyltetrahydropterin to 1'-oxo-2'-D-hydroxypropyl-H4-pterin. These results are clear demonstration of the in vivo synthesis of DH4 via 1'-oxo-2'-D-hydroxypropyl-H4-pterin as well as an alternative synthesis of BH4 and DH4 in the complete absence of SR.

Expression, purification, crystallization and preliminary X-ray analysis of sepiapterin reductase from Chlorobium tepidum

Sepiapterin reductase from Chlorobium tepidum (CT-SR) produces L-threo-tetrahydrobiopterin, an isomer of tetrahydrobiopterin, in the last step of de novo synthesis initiating from GTP. Native CT-SR and a selenomethionine (SeMet) derivative of CT-SR have been crystallized by the hanging-drop vapour-diffusion method using PEG 400 as precipitant. CT-SR crystals belong to space group R32, with unit-cell parameters a = b = 201.142, c = 210.184 A, and contain four molecules in the asymmetric unit. Diffraction data were collected to 2.1 A resolution using synchrotron radiation. The structure of CT-SR has been determined using MAD phasing. There is one CT-SR tetramer in the asymmetric unit formed by two closely interacting CT-SR dimers. The solvent content is calculated to be about 67.2%.

Sepiapterin reductases from Chlorobium tepidum and Chlorobium limicola catalyze the synthesis of L-threo-tetrahydrobiopterin from 6-pyruvoyltetrahydropterin

The ORF sequences of the gene encoding sepiapterin reductase were cloned from the genomic DNAs of Chlorobium tepidum and Chlorobium limicola, which are known to produce L-threo- and L-erythro-tetrahydrobiopterin (BH4)-N-acetylglucosamine, respectively. The deduced amino acid sequence of C. limicola consists of 241 residues, while C. tepidum SR has three residues more at the C-terminal. The overall protein sequence identity was 87.7%. Both recombinant proteins generated from Escherichia coli were identified to catalyze reduction of diketo compound 6-pyruvoyltetrahydropterin to L-threo-BH4. This result suggests that C. limicola needs an additional enzyme for L-erythro-BH4 synthesis to yield its glycoside. The catalytic activity of Chlorobium SRs also supports the previously proposed mechanism of two consecutive reductions of C1' carbonyl group of 6-pyruvoyltetrahydropterin via isomerization reaction.

Physarum polycephalum expresses a dihydropteridine reductase with selectivity for pterin substrates with a 6-(1', 2'-dihydroxypropyl) substitution

Physarum polycephalum is one of few non-animal organisms capable of synthesizing tetrahydrobiopterin from GTP. Here we demonstrate developmentally regulated expression of quinoid dihydropteridine reductase (EC 1.6.99.7), an enzyme required for recycling 6,7-[8H]-dihydrobiopterin. Physarum also expresses phenylalanine-4-hydroxylase activity, an enzyme that depends on dihydropteridine reductase. The 24.4 kDa Physarum dihydropteridine reductase shares 43% amino acid identity with the human protein. A number of residues important for function of the mammalian enzyme are also conserved in the Physarum sequence. In comparison to sheep liver dihydropteridine reductase, purified recombinant Physarum dihydropteridine reductase prefers pterin substrates with a 6-(1', 2'-dihydroxypropyl) group. Our results demonstrate that Physarum synthesizes, utilizes and metabolizes tetrahydrobiopterin in a way hitherto thought to be restricted to the animal kingdom.

Molecular cloning of a cDNA coding for GTP cyclohydrolase I from Dictyostelium discoideum

The GTP cyclohydrolase I (GTP-CH) gene of the cellular slime mould Dictyostelium discoideum has been cloned and sequenced. The 855 bp cDNA of this gene contains the open reading frame (ORF) encoding 232 amino acids with a predicted molecular mass of approx. 26 kDa. Southern blot analysis indicated the presence of a single gene for GTP-CH in Dictyostelium. PCR amplification of the ORF from chromosomal DNA and sequencing showed the existence of a 101 bp intron in the GTP-CH gene of Dictyostelium discoideum. The amino acid sequence has 47% and 49% positional identity to those of the human and yeast enzymes respectively. Most of the sequence variation between species is located in the N-terminal part of the protein. The overall identity with the E. coli protein is markedly lower. The enzyme was expressed in E. coli and purified as a 68 kDa fusion protein with the maltose-binding protein of E. coli. GTP-CH of Dictyostelium is heat-stable and showed maximal activity at 60 degrees C. The Km value for GTP is 50 microM.

Control of 6-(D-threo-1',2'-dihydroxypropyl) pterin (dictyopterin) synthesis during aggregation of Dictyostelium discoideum. Involvement of the G-protein-linked signalling pathway in the regulation of GTP cyclohydrolase I activity

6-(D-threo-1',2'-Dihydroxypropylpterin (dictyopterin) has been identified in extracts of growing Dictyostelium dicoideum cells [Klein, Thiery and Tatischeff (1990) Eur. J. Biochem. 187, 665-669]. We demonstrate that it originates from GTP by de novo biosynthesis and that the first committed step is catalysed by GTP cyclohydrolase I, yielding dihydroneopterin triphosphate [neopterin is 6-(D-erythro-1',2',3'-trihydroxypropyl) pterin]. The GTP cyclohydrolase I activity is found in the cytosolic fraction and in a membrane-associated form. The level of a 0.9 kb mRNA coding for GTP cyclohydrolase I decreases to about 10% of its initial value within 2 h after Dictyostelium cells start development induced by starvation. In the cytosolic fraction, the specific activities of GTP cyclohydrolase I, as well as the concentrations of (6R/S)-5,6,7,8-tetrahydrodictyopterin (H4dictyopterin), follow this decline of the mRNA level. In the particulate fraction, however, the specific activities of GTP cyclohydrolase I and, in consequence, H4dictyopterin synthesis, transiently increase and reach a maximum after 4-5 h of development. The time-course of H4dictyopterin concentrations in the starvation medium closely correlates with its production in the membrane fraction. The activity of membrane-associated GTP cyclohydrolase I can be increased by pre-incubation of the cell lysate with guanosine 5'-[gamma-thio]triphosphate and Mg2+. This GTP analogue does not serve as a substrate and has no direct effect on the enzyme activity, indicating that a G-protein-linked signalling pathway is involved in the regulation of GTP cyclohydrolase I activity and thus in H4dictyopterin production during early development of D. discoideum.

Integration of signaling information in controlling cell-fate decisions in Dictyostelium

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Pteridine biosynthesis and nitric oxide synthase in Physarum polycephalum

Physarum polycephalum, an acellular slime mould, serves as a model system to study cell-cycle-dependent events since nuclear division is naturally synchronous. This organism was shown to release isoxanthopterin which is structurally related to tetrahydrobiopterin, a cofactor of aromatic amino acid hydroxylases and of nitric oxide synthases (NOSs) (EC 1.14.13.39). Here, we studied Physarum pteridine biosynthesis in more detail and found that high amounts of tetrahydrobiopterin are produced and NOS activity is expressed. Physarum pteridine biosynthesis is peculiar in as much as 7,8-dihydroneopterin aldolase (EC 4.1.2.25), an enzyme of folic acid biosynthesis usually not found in organisms producing tetrahydrobiopterin, is detected in parallel. NOS purified from Physarum depends on NADPH, tetrahydrobiopterin and flavins. Enzyme activity is independent of exogenous Ca2+ and is inhibited by arginine analogues. The purified enzyme (with a molecular mass of 130 kDa) contains tightly bound tetrahydrobiopterin and flavins. During the synchronous cell cycle of Physarum, pteridine biosynthesis increases during S-phase whereas NOS activity peaks during mitosis, drops at telophase and peaks again during early S-phase. Our results characterize Physarum pteridine biosynthesis and NOS and suggest a possible link between NOS activity and mitosis.

The G alpha subunit G alpha 4 couples to pterin receptors and identifies a signaling pathway that is essential for multicellular development in Dictyostelium

In this paper, we show that the G alpha subunit G alpha 4 couples to pterin receptors and identifies a signalling pathway that is essential for multicellular development in Dictyostelium. G alpha 4 is developmentally regulated, is essential for proper morphogenesis and spore production, and functions cell nonautonomously. We show that G alpha 4 is coupled to receptors (alpha FAR) that activate chemotaxis and adenylyl and guanylyl cyclases in response to folate during the early stages of development and to a late class of folate receptors (beta FAR) that have different specificities for pterins. G alpha 4 is preferentially expressed in cells randomly distributed within the aggregate that are a component of the anterior-like cell population, and it is not detectably expressed in prespore cells. Our results suggest that an endogenous factor, possibly a pterin, produced during multicellular development is a requisite signal for multicellular development, acting through G alpha 4. We propose that the G alpha 4-expressing cells function as a regulatory cell type controlling prespore cell fate, possibly in response to an endogenous pterin. Our results indicate that G alpha 4 and G alpha 2 have parallel functions in mediating cellular responses to folate (pterins) and cAMP, respectively.

Chiral lumazines: preparation, properties, enantiomeric separation

Optically active lumazines (biolumazine, dictyolumazine, monalumazine, and neolumazine) are prepared from the corresponding pterins by enzymatic reaction, using pterin deaminase excreted by Dictyostelium discoideum. The fluorescence properties, circular dichroism spectra, and chromatographic behavior of these lumazines are studied. D- and L-enantiomers of biolumazine, dictyolumazine, and monalumazine are separated using a chiral flavoprotein column. This column also separates the enantiomeric pterins of the threo form: monapterin and dictyopterin. However, the column does not separate the enantiomeric pterins of the erythro form: neopterin and biopterin. By coupling a reverse-phase column to the flavoprotein column, the separation of pterins and lumazines in function of their hydrophobicity, as well as the separation of the diastereomers, is achieved. This coupled achiral/chiral high-performance liquid chromatography method enables determination of the stereoconfiguration of natural lumazines by comparison with optically pure compounds. A lumazine derivative, present in the extracellular medium of Dictyostelium discoideum, is identified as D-dictyolumazine, i.e., 6-(D-threo-1,2-dihydroxypropyl)-lumazine.

Determination of the stereoconfiguration of natural pterins by chiral high-performance liquid chromatography

The separation of D- and L-enantiomers of 6-(polyhydroxypropyl)pterins was obtained by ligand-exchange chromatography using a reversed-phase column at 12 degrees C with a mobile phase containing D-phenylalanine as the chiral modifier and Cu(II) as the metal ion. This allowed the determination of the stereoconfiguration of natural pterins from very small amounts of biological sample containing pterins in the picomole range (nanogram range). Fluorescence detection was used both to increase the sensitivity and to confirm the identification by on-line fluorescence spectroscopy and comparison with reference compounds. The stereoconfiguration of optically active pterins present in a bacterium (Escherichia coli), in a ciliate protozoan (Tetrahymena pyriformis), in an amoeba (Dictyostelium discoideum), and in mammals (human urine) was obtained and compared to earlier determinations. Incidental findings resulting from the application of this method were that human urinary monapterin and the major pterin of T. pyriformis were identified as a D-monapterin, which, until now, was not known as a natural pterin.

The major pterin in Tetrahymena pyriformis is 6-(D-threo-1,2,3-trihydroxypropyl)-pterin (D-monapterin) and not 6-(L-threo-1,2-dihydroxypropyl)-pterin (ciliapterin)

The major pterin in Tetrahymena pyriformis, strain W, earlier suggested to be L-threo-biopterin and named ciliapterin [1] is now identified as D-threo-neopterin (D-monapterin). This is the first example of a natural D-monapterin. This compound was characterized by its chromatographic behavior, its fluorescence properties and by its oxidation product with alkaline permanganate. The final identification was obtained by comparison with an authentic material using an exchange ligand chromatography method with D-phenylalanine as chiral modifier and Cu (II) as metal ion. D-monapterin is also present as the major pterin in Tetrahymena pyriformis strains GL and ST, and in Tetrahymena thermophila.