The nature of the multiple forms of triphosphate synthetase

Jackson, Raymond J.; Shiota, Tetsuo

doi:10.1016/0005-2744(75)90025-x

“…Several of th~se atypical PKU patients a=e responsive to BH 4 administration alone (12). and (17,18) and other invertebrates (19,20,21,22,23), an enzyme system was isolated that was not Mg++-dependent and converted guanosine triphosphate (GTP) directly to D-erythro-dihydroneopterin triphosphate (NH 2 TP) this enzyme was named GTP-cyclohydrolase I.…”

Section: Introductionmentioning

confidence: 99%

Tetrahydrobiopterin Biosynthesis

Curtius¹,

Häusermann²,

Niederwieser³

et al. 1982

March 7–10, 1982, St. Christoph, Arlberg, Austria

1

0

View full text Add to dashboard Cite

The biosynthesis of tetrahydrobiopterin from either dihydroneopterin triphosphate, sepiapterin, dihydrosepiapterin or dihydrobiopterin was investigated using extracts from human liver, dihydrofolate reductase and purified sepiapterin reductase from human liver and rat erythrocytes. The incorporation of hydrogen in tetrahydrobiopterin was studied in either 2H2O or in H2O using unlabeled NAD(P)H or (R)‐(4‐2H)NAD(P)H or (S)‐(4‐2H)NAD(P)H. Dihydrofolate reductase catalyzed the transfer of the pro‐R hydrogen of NAD(P)H during the reduction of 7,8‐dihydrobiopterin to tetrahydrobiopterin. Sepiapterin reductase catalyzed the transfer of the pro‐S hydrogen of NADPH during the reduction of sepiapterin to 7,8‐dihydrobiopterin. In the presence of partially purified human liver extracts one hydrogen from the solvent is introduced at position C(6) and the 4‐pro‐S hydrogen from NADPH is incorporated at each of the C(1′) and C(2′) position of BH4. Label from the solvent is also introduced into position C(3′). These results suggest that dihydrofolate reductase is not involved in the biosynthesis of tetrahydrobiopterin from dihydroneopterin triphosphate. They are consistent with the assumption of the occurrence of a 6‐pyruvoyl‐tetrahydropterin intermediate, which is proposed to be formed upon triphosphate elimination from dihydroneopterin triphosphate, and via an intramolecular redox reaction. Our results suggest that the reduction of 6‐pyruvoyl‐tetrahydropterin might be catalyzed by sepiapterin reductase.

show abstract

“…FH 4 serves as a coenzyme for a variety of one-carbon transfer reactions (26), while BH 4 functions as an essential reducing cofactor for NOSs, glyceryl ether mono-oxygenases, and mammalian aromatic amino acid hydroxylases (23,29,36,37). Bacterial GTPCHs from Escherichia coli (44), Bacillus subtilis (10), Lactobacillus plantarum (17), and Serratia indica (21) are all known in folate biosynthetic pathways. Streptomyces tubercidicus (46) contains a GTP-8-formylhydrolase involved in the formation of pyrrolopyrimidine nucleoside antibiotics, an enzyme that cleaves the diazole ring but does not cyclize the product to produce pteridines as the final product.…”

mentioning

confidence: 99%

GTPCyclohydrolaseI

Nar¹

2004

Handbook of Metalloproteins

View full text Add to dashboard Cite

GTP cyclohydrolase I (GTPCH) catalyzes the first step in pteridine biosynthesis in Nocardia sp. strain NRRL 5646. This enzyme is important in the biosynthesis of tetrahydrobiopterin (BH 4 ), a reducing cofactor required for nitric oxide synthase (NOS) and other enzyme systems in this organism. GTPCH was purified more than 5,000-fold to apparent homogeneity by a combination of ammonium sulfate fractionation, GTP-agarose, DEAE Sepharose, and Ultragel AcA 34 chromatography. The purified enzyme gave a single band for a protein estimated to be 32 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The molecular mass of the native enzyme was estimated to be 253 kDa by gel filtration, indicating that the active enzyme is a homo-octamer. The enzyme follows Michaelis-Menten kinetics, with a K m for GTP of 6.5 M. Nocardia GTPCH possessed a unique N-terminal amino acid sequence. The pH and temperature optima for the enzyme were 7.8 and 56°C, respectively. The enzyme was heat stable and slightly activated by potassium ion but was inhibited by calcium, copper, zinc, and mercury, but not magnesium. BH 4 inhibited enzyme activity by 25% at a concentration of 100 M. 2,4-Diamino-6-hydroxypyrimidine (DAHP) appeared to competitively inhibit the enzyme, with a K i of 0.23 mM. With Nocardia cultures, DAHP decreased medium levels of NO 2 ؊ plus NO 3 ؊ . Results suggest that in Nocardia cells, NOS synthesis of nitric oxide is indirectly decreased by reducing the biosynthesis of an essential reducing cofactor, BH 4 .

show abstract

“…FH 4 serves as a coenzyme for a variety of one-carbon transfer reactions (26), while BH 4 functions as an essential reducing cofactor for NOSs, glyceryl ether mono-oxygenases, and mammalian aromatic amino acid hydroxylases (23,29,36,37). Bacterial GTPCHs from Escherichia coli (44), Bacillus subtilis (10), Lactobacillus plantarum (17), and Serratia indica (21) are all known in folate biosynthetic pathways. Streptomyces tubercidicus (46) contains a GTP-8-formylhydrolase involved in the formation of pyrrolopyrimidine nucleoside antibiotics, an enzyme that cleaves the diazole ring but does not cyclize the product to produce pteridines as the final product.…”

mentioning

confidence: 99%

GTPCyclohydrolase I: Purification, Characterization, and Effects ofInhibition on Nitric Oxide Synthase in Nocardia Species

He

¹

,

Rosazza

²

2003

Appl Environ Microbiol

View full text Add to dashboard Cite

GTP cyclohydrolase I (GTPCH) catalyzes the first step in pteridine biosynthesis in Nocardia sp. strain NRRL 5646. This enzyme is important in the biosynthesis of tetrahydrobiopterin (BH 4 ), a reducing cofactor required for nitric oxide synthase (NOS) and other enzyme systems in this organism. GTPCH was purified more than 5,000-fold to apparent homogeneity by a combination of ammonium sulfate fractionation, GTP-agarose, DEAE Sepharose, and Ultragel AcA 34 chromatography. The purified enzyme gave a single band for a protein estimated to be 32 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The molecular mass of the native enzyme was estimated to be 253 kDa by gel filtration, indicating that the active enzyme is a homo-octamer. The enzyme follows Michaelis-Menten kinetics, with a K m for GTP of 6.5 M. Nocardia GTPCH possessed a unique N-terminal amino acid sequence. The pH and temperature optima for the enzyme were 7.8 and 56°C, respectively. The enzyme was heat stable and slightly activated by potassium ion but was inhibited by calcium, copper, zinc, and mercury, but not magnesium. BH 4 inhibited enzyme activity by 25% at a concentration of 100 M. 2,4-Diamino-6-hydroxypyrimidine (DAHP) appeared to competitively inhibit the enzyme, with a K i of 0.23 mM. With Nocardia cultures, DAHP decreased medium levels of NO 2 ؊ plus NO 3 ؊ . Results suggest that in Nocardia cells, NOS synthesis of nitric oxide is indirectly decreased by reducing the biosynthesis of an essential reducing cofactor, BH 4 .A tetrahydrobiopterin (BH 4 )-dependent bacterial nitric oxide synthase (NOS), designated NOS Noc , was first purified and characterized in Nocardia sp. strain NRRL 5646 in our laboratory (7). Continued pursuit of the possible roles of NOS resulted in the demonstration of guanylate cyclase (GC) activity in this bacterium (34). With viable Nocardia cells, additions of BH 4 plus arginine enhanced GC activity and the amounts of cyclic GMP eightfold. This work established a novel role for NOS Noc in Nocardia similar to that known to exist in higher life forms.

show abstract

The nature of the multiple forms of triphosphate synthetase

Cited by 14 publications

References 30 publications

Tetrahydrobiopterin Biosynthesis

Tetrahydrobiopterin Biosynthesis

GTPCyclohydrolaseI

GTPCyclohydrolase I: Purification, Characterization, and Effects ofInhibition on Nitric Oxide Synthase in Nocardia Species

Contact Info

Product

Resources

About