Xanthommatin biosynthesis in wild-type and mutant strains of the Australian sheep blowfly Lucilia cuprina

The synthesis of eye pigments has been studied in the seven eye color mutants of the Australian sheep blowfly, Lucilia cuprina. Six appear to be affected primarily in the synthesis of xanthommatin. In wild type, the onset of xanthommatin biosynthesis occurs midway through metamorphosis. Developmental patterns of accumulation of the xanthommatin precursors tryptophan, kynurenine, and 3-hydroxykynurenine have also been established for wild type. By determining the levels of these precursors in late pupae of the mutants, it has been shown that the mutant yellowish accumulates excess tryptophan and the mutant yellow accumulates excess kynurenine. The implications of these results—that yellowish lacks tryptophan oxygenase, thus failing to convert tryptophan to kynurenine, and that yellow lacks kynurenine hydroxylase (blocked in the conversion of kynurenine to 3-hydroxykynurenine)—have been confirmed. This has involved in vitro assays of tryphophan oxygenase and precursor feeding experiments. The precursor accumulation patterns are less clear for the other mutants.     

Transport defects as the physiological basis for eye color mutants of Drosophila melanogaster

Kynurenine-H ³ transport and conversion to 3-hydroxykynurenine were studied in organ culture using the Malpighian tubules and developing eyes from wild type and the eye color mutants w, st, 1td, ca, and cn of Drosophila melanogaster. Malpighian tubules from wild type have the ability to concentrate kynurenine and convert it to 3-hydroxykynurenine. The tubules from w, st, 1td, and ca are deficient in the ability to transport kynurenine, as are the eyes of the mutants w, st, and 1td. This defect in kynurenine transport provides a physiological explanation for the phenotypic properties of the mutants. The relationship of these measurements to previous observations on these eye color mutants is discussed and the transport defect hypothesis is consistently supported. We have concluded that several of the eye color mutants in Drosophila are transport mutants.     

Genetic and functional analysis of tryptophan transport in Malpighian tubules of Drosophila

Dissected Malpighian tubules from wild type and the eye color mutant white of Drosophila were compared with respect to their abilities to transport tryptophan and kynurenine into tubule cells. It was determined that mutation at white greatly impairs the ability of Malpighian tubule cells to take up tryptophan. Functional studies on the extracellular spaces and ultrastructural observations indicated no differences in these respects between wild type and white tubules. It is consistent with several observations that much of the tryptophan associated with white exists in the intercellular spaces. Furthermore, the uptake of tryptophan by the w ⁺ system of wild type tubules is inhibited by the analogue 5-methyl-tryptophan. However, the incorporation of radioactive tryptophan into protein in tubule cells from wild type and white occurs at the same rates and is not affected by 5-methyl-tryptophan. Therefore, it is apparent that Malpighian tubules have a transport system that enables entry of tryptophan into a cellular pool and that this cellular pool is initially independent of the tryptophan pool used for protein synthesis. The mutant white lacks this transport system. From these studies and others it appears that compartmentalization of cellular pools may be brought about via the utilization of specific membrane transport systems.     

A specific and sensitive fluorometric assay for tryptophan oxygenase

A spectrophotofluorometric assay was used to measure tryptophan oxygenase activity in several species. The fluorescent assay depends on the conversion of the product of the reaction, N-formyl-l-kynurenine, to anthranilate by means of the coupling enzymes kynurenine formamidase and kynureninase. These enzymes are easily obtained from l-tryptophan-induced N. crassa; and the product, anthranilate, is readily separated by organic extraction from other tryptophan catabolites and easily identified fluorometrically. With this assay, tryptophan oxygenase has been demonstrated in vitro for the first time in N. crassa.     

Influence of strain and stage of development on three enzymes in the tryptophan to nicotinamide adenine dinucleotide pathway of mice

Summary In an attempt to obtain an animal model to study the carcinogenicity and toxicity of the endogenously synthesized orthoaminophenols L-3-hydroxykynurenine and 3-hydroxyanthranilate, ten inbred strains of mice were examined with respect to sex, stage of development, and strain variability for differences in hepatic levels of activity of kynurenine formamidase, hydroxykynureninase, and hydroxyanthranilate oxygenase. No significant differences for these three enzymes were found between males and females. Kynurenine formamidase and hydroxykynureninase increased in activity five-to tenfold from birth to maturity (30 days), whereas hydroxyanthranilate oxygenase remained at a constant high level of activity (300 to 1500 times that of hydroxykynureninase) throughout this period. Genetic regulation of kynurenine formamidase was indicated by the finding that when a strain with high activity was crossed to a strain with low activity, the F₁ hybrid had an intermediate level of activity. Some differences in activity among strains were found for hydroxykynureninase, but it remains to be seen whether these differences may also be genetically determined. No significant differences in the level of activity were found among strains for hydroxyanthranilate oxygenase.Supported by National Cancer Institute Grant 1R01CA18817-01 and Minority Biomedical Support Grant RR-08111 from the NIH to Florida A & M UniversityOak Ridge National Laboratory is operated by the Union Carbide Corporation for the Energy Research and Development Administration     

Product induction in Pseudomonas acidovorans of a permease system which transports L-tryptophan

Growth of Pseudomonas acidovorans in the presence of l-tryptophan resulted in the appearance of a tryptophan transport system which was extremely sensitive to sodium azide or 2,4-dinitrophenol. Asparagine-grown cells possessed no detectable tryptophan "permease" activity. Substitution of l-kynurenine for l-tryptophan in the growth medium also induced the tryptophan permease activity, along with tryptophan oxygenase and kynurenine formamidase. This is the first reported example of the product induction of a permease activity. Irrespective of whether Pseudomonas cells are grown in the presence of d- or l-tryptophan, the resulting induced tryptophan permease activity is specific for the l-isomer. In addition, the radioactive compounds l-leucine, l-phenylalanine, or dl-5-hydroxytryptophan are not transported. When dl-5-fluorotryptophan is a component of the inducing medium (with l-tryptophan), induction of tryptophan permease activity, as well as tryptophan oxygenase, is inhibited. In the permease assay system, using normally induced cells, the fluoroanalogue inhibited strikingly tryptophan transport. Therefore, this analogue may inhibit induction by blocking inducer transport into the cell. When added to the l-tryptophan-inducing medium, dl-7-azatryptophan markedly enhanced induction of tryptophan oxygenase, but the level of tryptophan permease activity was not further elevated. The mechanism of this analogue is unclear at present. Invariant tryptophan permease activity levels are found in cells grown with 5 or 15 mml-tryptophan or 5 mml-kynurenine, whereas the respective tryptophan oxygenase levels are greatly different. Together with other results, these results indicate that the synthesis of tryptophan permease activity is not coordinate with that of tryptophan oxygenase. Tryptophan transport is strongly inhibited by l-formylkynurenine and by l-kynurenine. These two metabolites were prepared in radioactive form, and they are actively transported following bacterial growth on l-tryptophan or l-kynurenine. Preliminary results suggest the tryptophan permease activity may be distinct from the permease(s) activity for l-formylkynurenine and l-kynurenine. Kynurenine, then, is capable of inducing tryptophan permease and kynurenine permease activities.     

Purine transport by Malpighian tubules of pteridine-deficient eye color mutants of Drosophila melanogaster

Uptakes of guanine into Malpighian tubules of wild-type Drosophila and the eye color mutants white (w), brown (bw), and pink-peach (p ^p) have been compared. Tubules for each of these mutants are unable to concentrate guanine intracellularly. The transport of xanthine and riboflavin is also deficient in w tubules. The transport of guanosine, adenine, hypoxanthine, and guanosine monophosphate is similar in wild-type and white Malpighian tubules. These data and other information about these mutants make it likely that these pteridine-deficient eye color mutants do not produce pigments because of the inability to transport a pteridine precursor. This view supports the hypothesis that mutants which lack both pteridine and ommochromes do so because precursors to both classes of pigments share a common transport system.This work was supported by Grant GM22366 from NIH.     

Purification and characterization of kynurenine formamidase activities from Streptomyces parvulus

Two forms of kynurenine formamidase (EC 3.5.1.9; aryl-formylamine amidohydrolase) are present in extracts of Streptomyces parvulus. The higher molecular weight enzyme (Mr = 42 000), kynurenine formamidase I, appears to be constitutive and is present at relatively constant but low levels in antibiotic producing and nonproducing cultures, whereas the synthesis of the lower molecular weight form (Mr = 25 000), kynurenine formamidase II, is initiated just prior to the onset of actinomycin formation. It is postulated (i) that kynurenine formamidase II catalyzes the second step in the pathway from tryptophan----actinocin, and (ii) that it is regulated specifically for the specialized function of actinomycin biosynthesis. The role of kynurenine formamidase I is unknown. Formamidase I and II activities were purified from extracts of S. parvulus and kinetic parameters of the two enzymes were determined. Although some of the properties of the two enzymes are quite similar (substrate specificities, Km values), some striking differences were noted (pH and temperature optima, molecular size, chromatographic properties, sensitivity to certain ions and chemicals). Mutant studies suggest that expression of the gene(s) coding for formamidase II activity play an essential role in regulating the formation of actinocin and, hence, antibiotic synthesis. Kynurenine formamidase activity was also found in a representative number of Streptomyces species and related organisms suggesting that the enzyme may function in the degradative metabolism of tryptophan by certain actinomycetes in nature.     

Dosage compensation and ontogenic expression of suppressed and transformed Vermilion flies in Drosophila

A spectrofluorometric assay system for tryptophan oxygenase was used to compare dosage compensation properties and ontogenic expression of suppressed, “transformed,” and wild-type vermilion flies. The results indicate that, although different stocks showed different levels of oxygenase activity, all showed dosage compensation properties. The ontogenic expression of tryptophan oxygenase was observed to be different in the various genotypes. Whereas suppressed vermilion resembled wild type in its pattern, the ontogenic profiles of “transformed” flies were different.     

FACTORS AFFECTING THE INTRACELLUALR SYNTHESIS OF KYNURENINE

Near the time of pupation, autofluorescent kynurenine globules appear in the cells in the anterior region of the fatbody of Drosophila melanogaster. It has been reported previously that kynurenine synthesis may be induced in an additional group of fat cells by feeding the precursor tryptophan to Drosophila larvae, and that this induction of kynurenine production viewed within the fat cells is correlated with an increase in tryptophan pyrrolase activity. In the present report, conditions are outlined which result in the appearance of kynurenine in all of the fat cells. The number of cells in the fatbody which contain kynurenine is influenced by the quantity of tryptophan included in the diet, as well as by the developmental stage at the time of treatment and the duration of the feeding period on the inducer. Physical barriers modifying permeability, such as the membranous layer noted surrounding the fatbody, may be a factor in the regulation of the time and nature of the cellular induction of kynurenine synthesis. Another factor to be considered is the possibility of interference with the availability of tryptophan as a substrate or inducer for this synthesis within the cell. It is suggested that the occurrence of pteridines in some of the fat cells may modify the response of these cells to produce kynurenine, since pteridines as electron acceptors can complex with tryptophan as an electron donor. Kynurenine may be produced in the fat cells under in vitro conditions when they are incubated with L-tryptophan, but kynurenine is not formed when fat cells are incubated with D-tryptophan. The in vitro studies further demonstrate that induction of kynurenine synthesis may occur in fat cells isolated from young larvae in contrast, to in vivo conditions in which inducer does not effect an earlier appearance of kynurenine in the larval fatbody.     

Regulation of the synthesis of enzymes of tryptophan dissimilation in Acinetobacter calcoaceticus

Summary Acinetobacter calcoaceticus dissimilates tryptophan via the -ketoadipate pathway. The first enzyme, tryptophan oxygenase (l-tryptophan: oxygen oxidoreductase; EC 1.13.1.12), is substrate-induced by tryptophan. The second two enzymes, formamidase (aryl-formylamine amidohydrolase; EC 3.5.1.9) and kynureninase (l-kynurenine hydrolase; EC 3.7.1.3), are induced by the next intermediate, kynurenine. The last enzyme specific to tryptophan dissimilation, anthranilate oxidase, is substrate induced. This inductive pattern is in marked contrast to the extensive coordinacy of enzyme synthesis characteristic of the remainder of the -ketoadipate pathway.     

MUTANT GENES REGULATING THE INDUCIBILITY OF KYNURENINE SYNTHESIS

Alterations in the cellular synthesis of kynurenine in the larval fatbody of Drosophila melanogaster may be obtained by feeding the precursor tryptophan or by changing the genotype. In the wild type Ore-R strain, autofluorescent kynurenine globules normally occur in the cells in the anterior regions of the fatbody designated as regions 1, 2, and 3. When tryptophan is included in the larval diet, kynurenine will develop throughout the entire fatbody, thus extending to the cells in regions 4, 5, and 6. In the fatbodies of both the sepia mutant strain and the mutant combinations of the suppressible vermilion alleles with the suppressor gene (su²-s, v¹ and su²-s, v²), kynurenine is found in the cells from region 1 through region 4. This involvement of additional cells in the synthesis of kynurenine occurs under the usual culture conditions for Drosophila. When sepia larvae are fed tryptophan, kynurenine appears in all of the cells of the fatbody. However, dietary tryptophan does not induce kynurenine production in cells in regions 5 and 6 in the mutant combination su²-s, v¹ or su²-s, v². In the latter strains, an increase in the quantity of kynurenine in the fatbody is detected, but this increase remains limited to the same cells in which kynurenine production is found under normal feeding conditions. When the v^36f allele is combined with the su²-s allele, an extremely faint autofluorescence characteristic of kynurenine is found in some of the anteriormost fat cells of regions 1 and 2. This autofluorescence becomes intensified when tryptophan is fed to su²-s, v^36f larvae. The genetic control of kynurenine synthesis in the cells of the fatbody of Drosophila melanogaster has been previously demonstrated. The present observations establish genetic regulation of the ability to induce kynurenine production within a cell through the administration of the inducer tryptophan. Kynurenine production has been considered as a unit function of the cell as a whole rather than of the enzyme alone, and it has been concluded that even though cells in different parts of the body perform this same function (kynurenine production), the gene loci regulating this function may be different for cells in different regions of the body. A phenomenon of overlapping domains of gene actions at the cellular level offers a genetic and cellular basis for developmental and physiological homeostasis.     

INTRACELLULAR LOCALIZATION OF KYNURENINE IN THE FATBODY OF DROSOPHILA

Light blue fluorescent globules accumulate in the cells of the anterior region of the fatbody of Drosophila larvae near the time of pupation. This fluorescent material appears in the Ore-R wild type strain as well as mutant strains in which the synthesis of both the red and brown eye pigments is affected. The vermilion mutant, which is characterized by the absence of the brown pigment component in the eye, was the only strain among those examined which did not develop the light blue fluorescent globules. Utilizing chromatographic techniques together with the information gained by examination of the mutant strains, the fluorescent material has been identified as kynurenine. Of particular interest is the manner of appearance of the fluorescent material in the vicinity of the nuclear membrane of the fat cells.     

Transient expression of the Drosophila melanogaster cinnabar gene rescues eye color in the white eye (WE) strain of Aedes aegypti

The lack of eye pigment in the Aedes aegypti WE (white eye) colony was confirmed to be due to a mutation in the kynurenine hydroxylase gene, which catalyzes one of the steps in the metabolic synthesis of ommochrome eye pigments. Partial restoration of eye color (orange to red phenotype) in pupae and adults occurred in both sexes when first or second instar larvae were reared in water containing 3-hydroxykynurenine, the metabolic product of the enzyme kynurenine hydroxylase. No eye color restoration was observed when larvae were reared in water containing kynurenine sulfate, the precursor of 3-hydroxykynurenine in the ommochrome synthesis pathway. In addition, a plasmid clone containing the wild type Drosophila melanogaster gene encoding kynurenine hydroxylase, cinnabar (cn), was also able to complement the kynurenine hydroxylase mutation when it was injected into embryos of the A. aegypti WE strain. The ability to complement this A. aegypti mutant with the transiently expressed D. melanogaster cinnabar gene supports the value of this gene as a transformation reporter for use with A. aegypti WE and possibly other Diptera with null mutations in the kynurenine hydroxylase gene.     

Mutations in structural genes of tryptophan metabolic enzymes of the kynurenine pathway modulate some units of the L-glutamate receptor-actin cytoskeleton signaling cascade

Methods of immunohistochemistry and fluorescent staining was used to study the localization and amounts of protein components of the signal cascade connecting the receptor link (NMDA-subtype glutamate receptor) with actin of the cytoskeleton in the head ganglia of Drosophila strain Canton-S (wild type, control) and strains carrying mutations vermilion, cinnabar, and cardinal, which sequentially inactivate tryptophanhydrolyzing enzymes during its metabolism into ommochrome. The obtained data are evidence for modulatory effects of genes controlling the kynurenine pathway of tryptophan metabolism on the major components of the signal cascade: the initial link (NMDA receptor, postsynaptic density protein-95, a structural protein involved in receptor localization and internalization), the intermediate link (limkinase-1, the key neuronal enzyme in actin remodeling) and the final link (f-actin, the critical factor in the morphogenesis of synaptic structures and, hence, in the processes of synaptic plasticity, learning and memory). It is suggested that kynurenine acid (an endogenous nonspecific antagonist of L-glutamate receptor) and 3-hydroxykynurenine capable of inducing a nonspecific stimulating effect are biochemical intermediates of the effects of these genes.     

Do organophosphate insecticides inhibit the conversion of tryptophan to NAD+ in ovo?

The hypothesis that organophosphate (OP) insecticides reduce the NAD+ levels of chick embryos by inhibiting kynurenine formamidase was tested. Fertile chicken eggs at 3 days of incubation were treated with a teratogenic dose of the organophosphate insecticide diazinon (DZN) in the presence or absence of exogenous L-tryptophan or nicotinamide, or one of the metabolic intermediates (L-kynurenine, 3-hydroxyanthranilic acid, quinolinic acid) between tryptophan and NAD+. By day 10 of development, DZN reduced the NAD+ content of the hind limbs of the embryos to less than 20% of normal and by day 15 it caused severe type I and type II teratogenic responses. The co-presence of tryptophan or one of its metabolites served to maintain the NAD+ levels of DZN-treated embryos close to or above normal and significantly alleviated the symptoms of type I teratisms. Tryptophan is virtually as effective as most of its metabolites in suppressing the effects of DZN on the NAD+ content and physical development of the embryos. This equivalence does not support the proposition that the inhibition of kynurenine formamidase causes the lowered NAD+ levels involved in OP-induced type I teratogenesis. It is consistent with the concept that the insecticide acts to decrease the availability of tryptophan to the embryo.     

Regulation of the Pathway for the Degradation of Anthranilate in Aspergillus niger

Studies were carried out to determine the factors governing the induction of anthranilate hydroxylase and other enzymes in the pathway for the dissimilation of anthranilate by Aspergillus niger (UBC 814). The enzyme was induced by growth in the presence of tryptophan, kynurenine, anthranilate, and, surprisingly, by 3-hydroxyanthranilate, which was not an intermediate in the conversion of anthranilate to 2,3-dihydroxybenzoate. There was an initial lag in the synthesis of anthranilate hydroxylase when induced by tryptophan, anthranilate, and 3-hydroxyanthranilate. Cycloheximide inhibited the enzyme induction. Comparative studies on anthranilate hydroxylase, 2,3-dihydroxybenzoate carboxy-lyase, and catechol 1:2-oxygenase revealed that these enzymes were not coordinately induced by either anthranilate or 3-hydroxyanthranilate. Structural requirements for the induction of anthranilate hydroxylase were determined by using various analogues of anthranilate. The activity of the constitutive catechol oxygenase was increased threefold by exposure to anthranilate, 2,3-dihydroxybenzoate, or catechol. 3-Hydroxyanthranilate did not enhance the levels of catechol oxygenase activity.     

Tryptophan catabolism via kynurenine production in <Emphasis Type="Italic">Streptomyces coelicolor</Emphasis>: identification of three genes coding for the enzymes of tryptophan to anthranilate pathway

Most enzymes involved in tryptophan catabolism via kynurenine formation are highly conserved in Prokaryotes and Eukaryotes. In humans, alterations of this pathway have been related to different pathologies mainly involving the central nervous system. In Bacteria, tryptophan and some of its derivates are important antibiotic precursors. Tryptophan degradation via kynurenine formation involves two different pathways: the eukaryotic kynurenine pathway, also recently found in some bacteria, and the tryptophan-to-anthranilate pathway, which is widespread in microorganisms. The latter produces anthranilate using three enzymes also involved in the kynurenine pathway: tryptophan 2,3-dioxygenase (TDO), kynureninase (KYN), and kynurenine formamidase (KFA). In Streptomyces coelicolor, where it had not been demonstrated which genes code for these enzymes, tryptophan seems to be important for the calcium- dependent antibiotic (CDA) production. In this study, we describe three adjacent genes of S. coelicolor (SCO3644, SCO3645, and SCO3646), demonstrating their involvement in the tryptophan-to-anthranilate pathway: SCO3644 codes for a KFA, SCO3645 for a KYN and SCO3646 for a TDO. Therefore, these genes can be considered as homologous respectively to kynB, kynU, and kynA of other microorganisms and belong to a constitutive catabolic pathway in S. coelicolor, which expression increases during the stationary phase of a culture grown in the presence of tryptophan. Moreover, the S. coelicolor ΔkynU strain, in which SCO3645 gene is deleted, produces higher amounts of CDA compared to the wild-type strain. Overall, these results describe a pathway, which is used by S. coelicolor to catabolize tryptophan and that could be inactivated to increase antibiotic production.     

Synthesis,accumulation and excretion of kynurenine during the pupal and adult stages of Papilio xuthus

Changes of kynurenine levels in fat body, haemolymph and wings during the pupal stage of Papilio xuthus were determined. In fat body and haemolymph, free kynurenine begins to increase at the time of the onset of eye pigmentation, reaches a maximum at the stage of, or shortly after red spot appearance in the wings and then rapidly decreases. The bound form of kynurenine seems not to be present. In the wings, on the contrary, the bound form of kynurenine begins to increase shortly before the appearance of red spot and accumulates up to the time of emergence.Tryptophan oxygenase activity is greatest in the fat body, with less in the wings and haemolymph did not show any activity.At the emergence of the butterfly, a considerable amount of kynurenine is excreted in the meconium. Empty pupal cases also contain some kynurenine. At the same time in the adult, the yellow scales contain the largest amounts of kynurenine, and the adult body (minus yellow scales) also contain a considerable amount of kynurenine.All these results suggest the possibility that kynurenine is synthesized in the fat body, is transported through the haemolymph and accumulates as the bound form in the yellow scales. But the possibility cannot be ruled out that some kynurenine is synthesized in the wings.     

DEVELOPMENT OF EYE COLORS IN DROSOPHILA: SOME PROPERTIES OF THE HORMONES CONCERNED

The substance inducing the production of pigment in the eyes of vermilion brown mutants of Drosophila melanogaster has been shown to be a relatively stable chemical entity possessing true hormone-like activity. A simple method for obtaining hormone solutions has been developed involving extraction of dried wild type Drosophila pupae with ethyl alcohol and water. A logarithmic proportionality has been found to exist between the amount of hormone and the induced eye color. This relationship provides a simple method for the quantitative determination of hormone concentration in given extracts. Larvae and pupae of D. melanogaster contain an intracellular enzyme which inactivates the hormone in the presence of molecular oxygen. The hormone is not oxidized under ordinary conditions with either molecular oxygen or hydrogen peroxide. The hormone has been found to be an amphoteric compound with both acidic and basic groups and with a molecular weight between 400 and 600. The solubility and precipitation reactions of the hormone suggest its amino acid-like nature. However, the instability to heat, acid, and alkali, and its rather restricted occurrence indicate a rather complex specific structure.