Impact-induced muscle damage and urinary pterins in professional rugby: 7,8-dihydroneopterin oxidation by myoglobin.

Muscle damage caused through impacts in rugby union is known to increase oxidative stress and inflammation. Pterins have been used clinically as markers of oxidative stress, inflammation, and neurotransmitter synthesis. This study investigates the release of myoglobin from muscle tissue due to force-related impacts and how it is related to the subsequent oxidation of 7,8-dihydroneopterin to specific pterins. Effects of iron and myoglobin on 7,8-dihydroneopterin oxidation were examined in vitro via strong cation-exchange high-performance liquid chromatography (SCX-HPLC) analysis of neopterin, xanthopterin, and 7,8-dihydroxanthopterin. Urine samples were collected from 25 professional rugby players pre and post four games and analyzed for myoglobin by enzyme-linked immunosorbent assay, and 7,8-dihydroneopterin oxidation products by HPLC. Iron and myoglobin oxidized 7,8-dihydroneopterin to neopterin, xanthopterin, and 7,8-dihydroxanthopterin at concentrations at or above 10 µM and 50 µg/mL, respectively. All four games showed significant increases in myoglobin, neopterin, total neopterin, biopterin, and total biopterin, which correlated between each variable (P < 0.05). Myoglobin and iron facilitate 7,8-dihydroneopterin oxidation to neopterin and xanthopterin. In vivo delocalization of myoglobin due to muscle damage may contribute to oxidative stress and inflammation after rugby. Increased concentrations of biopterin and total biopterin may indicate production of nitric oxide and monoamine neurotransmitters in response to the physical stress.

Monitoring translocation of multisubunit RNA polymerase along the DNA with fluorescent base analogues.

Here we describe a direct fluorescence method that reports real-time occupancies of the pre- and post-translocated state of multisubunit RNA polymerase. In a stopped-flow setup, this method is capable of resolving a single base-pair translocation motion of RNA polymerase in real time. In a conventional spectrofluorometer, this method can be employed for studies of the time-averaged distribution of RNA polymerase on the DNA template. This method utilizes commercially available base analogue fluorophores integrated into template DNA strand in place of natural bases. We describe two template DNA strand designs where translocation of RNA polymerase from a pre-translocation to a post-translocation state results in disruption of stacking interactions of fluorophore with neighboring bases, with a concomitant large increase in fluorescence intensity.

Isothermal amplification of DNA using quadruplex primers with fluorescent pteridine base analogue 3-methyl isoxanthopterin.

We previously developed a method, known as quadruplex priming amplification (QPA), which greatly simplifies DNA amplification and quantification assays. QPA employs specific primers based on GGGTGGGTGGGTGGG (G3T) sequence, which upon polymerase elongation spontaneously dissociates from the target and folds into a stable quadruplex. Fluorescent nucleotide analogs, when incorporated into these primers, emit light upon quadruplex formation and permit simple, specific, and sensitive quantification without the attachment of probe molecules. Here, we studied optical [fluorescence and circular dichroism (CD)] and thermodynamic properties of the G3T sequence and variants incorporating 3-methylisoxanthopterin (3MI), a highly fluorescent nucleotide analog suitable for QPA. CD studies demonstrate that the incorporation of 3MI does not change the overall tertiary structure of G3T; however, thermal unfolding experiments revealed that it significantly destabilizes the quadruplex. Enzymatic studies revealed that Taq and Bst are practically unable to incorporate any nucleotides opposite to template 3MI. Based on this knowledge, we designed QPA assays with truncated targets that demonstrate efficient amplification around 55°C. Overall, these studies suggest that 3MI-based QPA is a useful assay for DNA amplification and detection.

Discovery and structure determination of the orphan enzyme isoxanthopterin deaminase .

Two previously uncharacterized proteins have been identified that efficiently catalyze the deamination of isoxanthopterin and pterin 6-carboxylate. The genes encoding these two enzymes, NYSGXRC-9339a ( gi|44585104 ) and NYSGXRC-9236b ( gi|44611670 ), were first identified from DNA isolated from the Sargasso Sea as part of the Global Ocean Sampling Project. The genes were synthesized, and the proteins were subsequently expressed and purified. The X-ray structure of Sgx9339a was determined at 2.7 A resolution (Protein Data Bank entry 2PAJ ). This protein folds as a distorted (beta/alpha)(8) barrel and contains a single zinc ion in the active site. These enzymes are members of the amidohydrolase superfamily and belong to cog0402 within the clusters of orthologous groups (COG). Enzymes in cog0402 have previously been shown to catalyze the deamination of guanine, cytosine, S-adenosylhomocysteine, and 8-oxoguanine. A small compound library of pteridines, purines, and pyrimidines was used to probe catalytic activity. The only substrates identified in this search were isoxanthopterin and pterin 6-carboxylate. The kinetic constants for the deamination of isoxanthopterin with Sgx9339a were determined to be 1.0 s(-1), 8.0 muM, and 1.3 x 10(5) M(-1) s(-1) (k(cat), K(m), and k(cat)/K(m), respectively). The active site of Sgx9339a most closely resembles the active site for 8-oxoguanine deaminase (Protein Data Bank entry 2UZ9 ). A model for substrate recognition of isoxanthopterin by Sgx9339a was proposed on the basis of the binding of guanine and xanthine in the active site of guanine deaminase. Residues critical for substrate binding appear to be conserved glutamine and tyrosine residues that form hydrogen bonds with the carbonyl oxygen at C4, a conserved threonine residue that forms hydrogen bonds with N5, and another conserved threonine residue that forms hydrogen bonds with the carbonyl group at C7. These conserved active site residues were used to identify 24 other genes which are predicted to deaminate isoxanthopterin.

Xanthopterin in the Oriental hornet (Vespa orientalis): light absorbance is increased with maturation of yellow pigment granules.

The Oriental hornet bears both brown and yellow colors on its cuticle. The brown component is contributed by the pigment melanin, which is dispersed in the brown cuticle and provides protection against insolation, while the yellow-colored part contains within pockets in the cuticle granules possessing a yellow pigment. These yellow granules (YG) are formed about 2 days prior to eclosion of the imago, and their production continues for about 3 days posteclosion. Xanthopterin is the main component of the granule and lends it its yellow color. Xanthopterin produces a characteristic excitation/emission maximum at 386/456 nm. Characterization by use of mass spectrometry showed the compound to have a molecular ion of 179, as expected from xanthopterin. Spectroscopic examination of the absorption of an entire stripe of yellow cuticle in the course of its metamorphosis revealed that the absorption steadily increases throughout the process to a maximal level of absorption about 3 days posteclosion. In the absence of the YG, the cuticle is permeable to the passage of all wavelengths within the visible range and to the UV range (290-750 nm) in all age groups of hornets. The newly ecloded hornets depart the nest to engage in activities requiring exposure to insolation only as the process of granule formation terminates, namely, when the layer of YG in the cuticle suffices to absorb all the harmful UV radiation.

Cytokine-mediated xanthine oxidase upregulation in chronic obstructive pulmonary disease's airways.

Reactive oxygen species have been reported to be involved in the airway inflammatory process of chronic obstructive pulmonary disease (COPD). The aim of this study was to quantify the activity of xanthine oxidase (XO), which generates a potent radical superoxide anion in COPD airways. Thirteen stable COPD patients and 10 healthy subjects participated in this study. We collected the epithelial lining fluid using a newly developed microsampling technique, and quantified of cytokines responsible for the XO gene upregulation. The XO activity was significantly increased in COPD patients compared with that in healthy subjects. A significant negative correlation was found between the XO activity and the %FEV1 values. The level of tumor necrosis factor-alpha, interleukin-1beta, and interferon-gamma in COPD patients was significantly higher than that in healthy subjects. Both the amount of tumor necrosis factor-alpha and interleukin-1beta were significantly correlated with the degree of XO activity. These results suggest that the XO activity is increased in COPD airways, possibly due to its gene upregulation by proinflammatory cytokines. Because the XO activity was significantly correlated with the degree of airway obstruction, these cytokine-XO production pathways may play a key role in the inflammation of COPD.

Use of pteridine nucleoside analogs as hybridization probes.

The pteridine nucleoside analog 3-methyl isoxanthopterin (3-MI) is highly fluorescent, with a quantum yield of 0.88, and it can be synthesized as a phosphoramidite and incorporated into oligonucleotides through a deoxyribose linkage. Within an oligonucleotide, 3-MI is intimately associated with native bases and its fluorescence is variably quenched in a sequence-dependent manner. Bend ing, annealing, binding, digestion or cleavage of fluorophore-containing oligonucleotides can be detected by monitoring changes in fluorescence properties. We developed a single step method for detecting annealing of complementary DNA sequences using 3-MI-containing oligonucleotides as hybridization probes. One of the complementary strands contains the fluorophore as an insertion and when annealing occurs, the fluorophore bulges out from the double strand, resulting in increased fluorescence intensity. We have examined the sequence dependency, optimal strand length and impact of multiple fluorophores per strand in terms of brightness and impact on the annealing process. We describe the application of this technique to the detection of positive PCR products using an HIV-1 detection system. This sequence-dependent hybridization technique can result in fluorescence intensity increases of up to 27-fold. Fluorescence intensity increases are only seen upon specific binding to bulge-generating complements, removing issues of high background from non-specific binding.

The pteridine pathway in zebrafish: regulation and specification during the determination of neural crest cell-fate.

This review describes pteridine biosynthesis and its relation to the differentiation of neural crest derivatives in zebrafish. During the embryonic development of these fish, neural crest precursor cells segregate into neural elements, ectomesenchymal cells and pigment cells; the latter then diversifying into melanophores, iridophores and xanthophores. The differentiation of neural cells, melanophores, and xanthophores is coupled closely with the onset of pteridine synthesis which starts from GTP and is regulated through the control of GTP cyclohydrolase I activity. De novo pteridine synthesis in embryos of this species increases during the first 72-h postfertilization, producing H4biopterin, which serves as a cofactor for neurotransmitter synthesis in neural cells and for tyrosine production in melanophores. Thereafter, sepiapterin (6-lactoyl-7,8-dihydropterin) accumulates as yellow pigment in xanthophores, together with 7-oxobiopterin, isoxanthopterin and 2,4,7-trioxopteridine. Sepiapterin is the key intermediate in the formation of 7-oxopteridines, which depends on the availability of enzymes belonging to the xanthine oxidoreductase family. Expression of the GTP cyclohydrolase I gene (gch) is found in neural cells, in melanoblasts and in early xanthophores (xanthoblasts) of early zebrafish embryos but steeply declines in xanthophores by 42-h postfertilization. The mechanism(s) whereby sepiapterin branches off from the GTP-H4biopterin pathway is currently unknown and will require further study. The surge of interest in zebrafish as a model for vertebrate development and its amenability to genetic manipulation provide powerful tools for analysing the functional commitment of neural crest-derived cells and the regulation of pteridine synthesis in mammals.

6-Tetrahydrobiopterin functions as a UVB-light switch for de novo melanogenesis.

(6R)-L-erythro 5,6,7,8-tetrahydrobiopterin (6-BH4) and its 7-isomer (7-BH4) function as uncompetitive inhibitors of human and mushroom tyrosinases. Stoichiometry for the binding of [3H]-labeled 6-BH4 to both tyrosinases has been established as 1:1. Stable complexation of 6-BH4 to tyrosinase appears to involve a hydrophilic conserved glutamic acid (Glu131) with a pKa = 4.7. Photo-oxidation by UVB-light and O2 reverses the inhibition of tyrosinase by 6-BH4 and 7-BH4 with the 6-BH4/tyrosinase complex being four-fold more photolabile than 7-BH4/tyrosinase. The photo-oxidation of 6-BH4 by UVB-light can be assessed spectrophotometrically with this reaction yielding 7,8-dihydroxanthopterin as the final product, 7,8-Dihydroxanthopterin neither binds to nor inhibits tyrosinase. By contrast, UVA light does not catalyze the photodegradation of 6-BH4. Taken together, our results indicate that the photo-oxidation of the tetrahydrobiopterins by UVB may represent a photo-switch in the regulation of tyrosinase activity to promote de novo melanogenesis.

Tetrahydrobiopterin loading test in xanthine dehydrogenase and molybdenum cofactor deficiencies.

The objectives of this study were to find additional diagnostic information for the evaluation of xanthine dehydrogenase deficiency and molybdenum cofactor deficiency. Patients were given an oral loading test with 10 mg/kg 5,6,7,8-tetrahydrobiopterin. Urine excretion of pterin and isoxanthopterin was measured by HPLC. Control subjects had a fairly constant ratio of urinary pterin/isoxanthopterin before (0.57-5.32) and after (0.55-4.55) 5,6,7,8-tetrahydrobiopterin loading. These ratios were increased to 33 and 22 in a patient with hereditary xanthinuria and to 570 and 8030 in a patient with molybdenum cofactor deficiency. Obligate heterozygotes had an entirely normal test result. Evidence was obtained for the in vivo involvement of xanthine dehydrogenase in the conversion of pterin to isoxanthopterin. This test could be a sensitive marker for the establishment of residual enzyme activity.

Determination of human plasma xanthine oxidase activity by high-performance liquid chromatography.

An assay for human plasma xanthine oxidase activity was developed with pterin as the substrate and the separation of product (isoxanthopterin) by high-performance liquid chromatography with a fluorescence detector. The reaction mixture consists of 60 microliters of plasma and 240 microliters of 0.2 M Tris-HCl buffer (pH 9.0) containing 113 microM pterin. With this assay, the activity of plasma xanthine oxidase could be easily determined despite its low activity. As a result, it could be demonstrated that the intravenous administration of heparin or the oral administration of ethanol did not increase plasma xanthine oxidase activity in normal subjects, and also that plasma xanthine oxidase activity was higher in patients with hepatitis C virus infection than in healthy subjects or patients with gout. In addition, a single patient with von Gierke's disease showed a marked increase in the plasma activity of this enzyme, relative to that apparent in normal subjects.

Incorporation of a fluorescent guanosine analog into oligonucleotides and its application to a real time assay for the HIV-1 integrase 3'-processing reaction.

We have synthesized a highly fluorescent (quantum yield 0.88) guanosine analog, (3-methyl-8-(2-deoxy-beta-D-ribofuranosyl) isoxanthopterin (3-Mi) in a dimethoxytrityl, phosphoramidite protected form, which can be site-specifically inserted into oligonucleotides through a 3',5'-phosphodiester linkage using an automated DNA synthesizer. Fluorescence is partially quenched within an oligonucleotide and the degree of quench is a function of the fluorophore's proximity to purines and its position in the oligonucleotide. As an example of the potential utility of this class of fluorophores, we developed a continuous assay for HIV-1 integrase 3'-processing reaction by incorporating 3-MI at the cleavage site in a double-stranded oligonucleotide identical to the U5 terminal sequence of the HIV genome. Integrase cleaves the 3'-terminal dinucleotide containing the fluorophore, resulting in an increase in fluorescence which can be monitored on a spectrofluorometer. Substitution of the fluorophore for guanosine at the cleavage site does not inhibit integrase activity. This assay is specific for the 3'-processing reaction. The change in fluorescence intensity is linear over time and proportional to the rate of the reaction. This assay demonstrates the potential utility of this new class of fluorophore for continuous monitoring of protein/DNA interactions.

Xanthopterin-induced renal dysfunction: a reversible model of crystal nephropathy.

Xanthopterin (XPT), an unconjugated pteridine compound, affects cell growth and differentiation. When injected into rats, XPT has caused changes that have been interpreted as renal growth and hypertrophy. In the present study, we investigated the effect of intraperitoneal administration of XPT on the renal function in the rat. XPT administration was associated with polyuria and a reversible form of nonoliguric acute renal failure (ARF), with renal function declining maximally after 2 days and returning to normal after 7 days. The polyuria was due, at least in part, to a concentrating defect that was vasopressin resistant. The ability of XPT to induce ARF was modulated by dietary salt intake, being enhanced by a low-sodium diet and prevented by a high sodium intake. Histological examination of the kidneys showed intratubular crystal deposition and acute tubule necrosis, suggesting that XPT induces crystal nephropathy. There was an increase in wet and dry weights of the kidney and an increased DNA/protein ratio, compatible with a hyperplastic response. Because the severity of other crystal nephropathies may be modulated by urine flow rate and pH, we studied the ability of water diuresis or alkaline diuresis to protect against XPT-induced ARF. Both water diuresis and HCO3 loading blunted the ability of XPT to decrease renal function. The change in renal function induced by XPT in the various groups was paralleled by corresponding changes in the levels of XPT-like substances in the kidney and by the amount of crystal deposition. Thus, XPT injection induces crystal nephropathy, the severity of which can be modulated by dietary salt intake, urine pH, and urine flow rate.

Studies of the reductive half-reaction of milk xanthine dehydrogenase.

The reductive half-reaction of milk xanthine dehydrogenase (XDH) with NADH and with xanthine has been studied at pH 7.5, 25 degree C. NADH reduces XDH to the two-electron reduced form at a rate of 18 s-1, independent of NADH concentration over the range studied. Further reduction by NADH to the four-electron state is inhibited by excess NADH. Subsequent binding of NADH to the four-electron reduced form of the enzyme causes the redistribution of one electron from the flavin to the molybdenum center. The four-electron reduced species reached through reduction by NADH is the same as the species obtained upon reaction of NAD with fully reduced XDH. In contrast, xanthine rapidly reduces XDH to the four-electron level; further reduction is comparatively slow and is inhibited by excess xanthine. Studies using substoichiometric xanthine show that the reaction of XDH with 1 equivalent of xanthine involves rapid substrate binding and rapid reduction of the molybdenum center of the enzyme. Before the release of urate from the molybdenum active site, an electron is transferred at 15 s-1 from the reduced molybdenum center to one of the iron-sulfur centers of XDH. Urate is then released at a rate of 13 s-1, followed by a rapid electron redistribution within the protein. The reductive half-reaction of XDH with xanthine is rate-limiting in xanthine/NAD turnover, which appears to occur between the two- and four-electron reduced enzyme species. The reduction of XDH by substoichiometric amounts of the fluorescent substrate xanthopterin was also studied. This reaction, monitored by changes in both absorbance and fluorescence, was found to involve the formation of two molybdenum complexes (an Eox.S complex and an Ered.P complex) followed by the release of the product, leucopterin.

Concentrations and patterns of released pterins of various animal cell cultures.

Neopterin, biopterin, pterin, 6-hydroxymethylpterin and isoxanthopterin were determined in the supernatants of various animal cell cultures. The different cell lines showed distinct variations in the concentrations as well as in the pattern and total amount of the released pterins. In cells from the same organ but from diverse species differences in pattern and release were found. Cell lines derived from primates had a high release of neopterin. A further difference resulted from the origin of fetal or adult organs. Neoplastic cell lines showed different patterns of pterins, dependent on the type of tumour. Primary cultures from embryonic bovine lung had the highest total amount of released pterins in all cell lines examined.

Pteridine formation during lectin-induced lymphocyte activation.

After iodine oxidation, biopterin, 6-hydroxymethylpterin, and 6-formylpterin were identified in mouse spleen lymphocytes by means of reverse-phase HPLC, Crithidia assay, and oxidative degradation. Concanavalin A activation induces a 30-fold increase in the pteridine amounts; biopterin as well as the sum of the carbinol and the aldehyde attain levels of 6-8 X 10(-12) mol/10(6) cells. The most rapid increase occurs during the first 24 hr. Thus, pteridine accumulation precedes the period of lymphocyte proliferation; maximum DNA synthesis was found after 72 hr. Biopterin remains largely inside the cells, whereas 6-hydroxymethylpterin and 6-formylpterin were found in the supernatant if the stimulated cells were subsequently incubated in a phosphate buffered salt solution (PBS). Isoxanthopterin was found in the PBS supernatant of control cells that previously were kept in medium alone rather than subjected to lectin stimulation. Only minimal amounts were found inside these cells, and this pterin was absent from the stimulated lymphocytes. The early increase in cellular pteridines and their differential release may well provide the basis for their modulating effect on interleukin-2 activity (Ziegler I, et al: Lymphokine Research 3:284, 1984).

Urinary dihydroxanthopterin in the diagnosis of malignant hyperphenylalaninemia and phenylketonuria.

Assessment of urinary dihydroxanthopterin is proposed as a simple method of recognition of patients with malignant hyperphenylalaninemia (MHPA). High levels of urinary dihydroxanthopterin are found in untreated patients with phenylketonuria (PKU) or with dihydropteridine reductase (DHPR) deficiency. After dietary control of the serum phenylalanine level in PKU, the urinary dihydroxanthopterin falls to near normal levels. In DHPR deficiency urinary dihydroxanthopterin levels are high even when serum phenylalanine levels are in the range achieved on dietary treatment. Low levels would be expected in patients with defects in tetrahydrobiopterin synthesis even before dietary treatment. Confirmation of the diagnosis of different forms of MHPA then requires more detailed studies, but dietary treatment of other PKU patients can proceed with confidence.