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Biomedical subjects

H C Curtius

Publications and source records attributed to H C Curtius.

At least 55 records · Page 3Linked to original sources
PubMed1985

Tetrahydrobiopterin biosynthesis. Studies with specifically labeled (2H)NAD(P)H and 2H2O and of the enzymes involved.

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 dihyroneopterin triphosphate, and via an intramolecular redox reaction. Our results suggest that the reduction of 6-pyruvoyl-tetrahydropterin might be catalyzed by sepiapterin reductase.

Affinity Labels↗
PubMed1985

Purification and properties of the phosphate eliminating enzyme involved in the biosynthesis of BH4 in man.

An enzyme catalyzing the elimination of triphosphate from 7,8-dihydroneopterin triphosphate in the presence of Mg2+ has been purified approx. 3000 fold from human liver. It has a molecular weight of approx. 63'000, a pI value of 4.4 - 4.6 and is stable at 80 degrees C for 5 min. This enzyme catalyzes the formation of tetrahydrobiopterin in the presence of sepiapterin reductase, Mg2+ and NADPH. It is thus possible, that it also catalyzes the internal oxidoreduction leading to formation of the intermediate 6-pyruvoyl-tetrahydropterin, suggesting that no further enzyme is obligatory for biosynthesis of tetrahydrobiopterin.

Biopterins↗
PubMed1985

Atypical phenylketonuria with "dihydrobiopterin synthetase" deficiency: absence of phosphate-eliminating enzyme activity demonstrated in liver.

An assay for the phosphate-eliminating enzyme (PEE) activity in liver was developed which required only 5-10 mg tissue. PEE catalyses the elimination of inorganic triphosphate from dihydroneopterin triphosphate, which is the second and irreversible step in the biosynthesis of tetrahydrobiopterin (BH4). In the presence of substrate, magnesium, NADPH, and a sepiapterin reductase fraction from human liver, PEE catalysed the formation of BH4 which was measured by HPLC and electrochemical detection. In adult human liver, a PEE activity of 1.02 +/- 0.134 microU/mg protein (mean +/- 1 SD; n = 5) was observed. In liver needle biopsy material from five patients with defective biopterin biosynthesis, no PEE activity was found (less than 2% and 6% of the control values, respectively). The presence of an endogenous inhibitor was excluded. In a patient who died without definite diagnosis and in a patient with beta-thalassaemia liver PEE activity was increased. Sepiapterin reductase activity was present in all cases. Results indicate that in "dihydrobiopterin synthetase" deficiency, the most frequent of the rare BH4-deficient variants of hyperphenylalaninaemia, the molecular defect consists in a defect of PEE.

Adult↗
PubMed1985

Biosynthesis of tetrahydrobiopterin in man.

The biosynthesis of tetrahydrobiopterin (BH4) from dihydroneopterin triphosphate (NH2P3) was studied in human liver extract. The phosphate-eliminating enzyme (PEE) was purified approximately 750-fold. The conversion of NH2P3 to BH4 was catalyzed by this enzyme in the presence of partially purified sepiapterin reductase. Mg2+ and NADPH. The PEE is heat stable when heated at 80 degrees C for 5 min. It has a molecular weight of 63 000 daltons. One possible intermediate 6-(1'-hydroxy-2'-oxopropyl)5,6,7,8-tetrahydropterin(2'-oxo-tetrahydropte rin) was formed upon incubation of BH4 in the presence of sepiapterin reductase and NADP+ at pH 9.0. Reduction of this compound with NaBD4 yielded monodeutero threo and erythro-BH4, the deuterium was incorporated at the 2' position. This and the UV spectra were consistent with a 2'-oxo-tetrahydropterin structure. Dihydrofolate reductase (DHFR) catalyzed the reduction of BH2 to BH4 and was found to be specific for the pro-R-NADPH side. The sepiapterin reductase catalyzed the transfer of the pro-S hydrogen of NADPH during the reduction of sepiapterin to BH2. In the presence of crude liver extracts the conversion of NH2P3 to BH4 requires NADPH. Two deuterium atoms were incorporated from (4S-2H)NADHP in the 1' and 2' position of the BH4 side chain. Incorporation of one hydrogen from the solvent was found at position C(6). These results are consistent with the occurrence of an intramolecular redox exchange between the pteridine nucleus and the side chain and formation of 6-pyruvoyl-5,6,7,8-tetrahydropterin(tetrahydro-1'-2'-dioxopterin) as intermediate.

Alcohol Oxidoreductases↗
PubMed1985

Differential diagnosis of tetrahydrobiopterin deficiency.

Six hundred and seventy-three children (483 newborns and 190 older selected children) were screened for tetrahydrobiopterin (BH4) deficiency by HPLC of urine pterins and BH4 load test. One patient with GTP cyclohydrolase I deficiency, 36 patients with dihydrobiopterin synthetase (DHBS) deficiency (of which six were in the newborn and 30 in the older children) and 14 with dihydropteridine reductase deficiency (DHPR) were found. All 37 patients with defective BH4 biosynthesis responded to a BH4 load by lowering of the elevated serum phenylalanine concentration but four of 14 patients with DHPR deficiency did not. Measurement of DHPR activity in blood spots on Guthrie cards is recommended. Since subvariants of patients with BH4 deficiency exist, homovanillic acid, 5-hydroxyindole acetic acid, pterins, phenylalanine, and tyrosine in cerebrospinal fluid should be measured for diagnosis and the control of therapy. The activity of the phosphate-eliminating enzyme (a key enzyme in BH4 biosynthesis and part of "DHBS") was measured in human liver and activities of approx. 1 n U (mg protein)-1 were found. In the liver biopsy of a patient with DHBS deficiency no activity (less than 3% of controls) was demonstrated.

Amino Acid Metabolism, Inborn Errors↗
PubMed1982

Atypical phenylketonuria with defective biopterin metabolism. Monotherapy with tetrahydrobiopterin or sepiapterin, screening and study of biosynthesis in man.

Administration of a single dose of tetrahydrobiopterin dihydrochloride, 10--20 mg/kg orally, to a patient with dihydrobiopterin deficiency led to disappearance of clinical symptoms for 4 days, normalization of urinary phenylalanine and serotonin and decrease of elevated neopterin for 2--3 days. A dose-dependent stimulation of serotonin production was observed. A similar effect was noted with even lower doses of L-sepiapterin. The patient is now under monotherapy with tetrahydrobiopterin . 2 HCl, 2.5 mg/kg daily. Other patients with this disease may not respond as well. Results of screening for tetrahydrobiopterin deficiency in 228 cases with hyperphenylalaninemia, including 140 newborns, are reported. There is evidence that biopterin biosynthesis in human kidney and liver proceeds via a dioxo compound and L-sepiapterin.

Biopterins↗
PubMed1982

Atypical phenylketonuria due to biopterin deficiency. Early treatment with tetrahydrobiopterin and neurotransmitter precursors, trials of monotherapy.

This report presents the first case where an infant with tetrahydrobiopterin deficiency has been identified by screening of newborns with hyperphenylalaninemia for tetrahydrobiopterin deficiency. Therapy with L-Dopa, 5-hydroxytryptophan, Carbidopa and tetrahydrobiopterin was started at the age of seven weeks while the child received a normal diet. At that time already muscular hypotonia was observed. The girl, now 2 1/2 years old, shows slight muscular hypotonia and hypomotility, short periods of hypertonic extension of the limbs, and retardation of sensomotor and mental development of about 6-8 months. Monotherapy with tetrahydrobiopterin dihydrochloride, 20-40 mg/kg b.w., diminished the muscular hypotonia. The effect lasted however for only about 1 day. While urinary serotonin and phenylalanine remained normal for at least 3 days and neopterin was only slightly elevated, urinary free dopamine however remained low. Similar results were obtained after 1',2'-diacetyl tetrahydrobiopterin dihydrochloride administration, 20 mg/kg b.w.

5-Hydroxytryptophan↗
PubMed1981

Mass fragmentographic determination of endogenous glycine and glutamic acid released in vivo from the pigeon optic tectum. Effect of electric stimulation of a midbrain nucleus.

Various investigations suggest glycine to be an inhibitory transmitter in the pigeon optic lobe in a pathway originating in the nucleus isthmi, pars parvocellularis (Ipc) terminating in the optic tectum. In order to obtain additional evidence for this hypothesis the in vivo release of endogenous glycine in the optic tectum upon electrical stimulation of Ipc was investigated. By perfusing the upper strata of the optic tectum with Ringer solution using a push-pull cannula endogenous amino acids released from the surrounding tissue were collected. Concentration of glycine and glutamic acid in the perfusates were determined by mass fragmentography of their N-pentafluoropropionyl hexafluoroisopropyl esters. Deuterium-labeled glycine and glutamic acid were used as internal standards for quantitative measurements. The resting release of glycine and glutamic acid was 2.9 pmol/min and 1.4 pmol/min, respectively. Electrical stimulation of Ipc was found to induce a 2--40-fold increase of the glycine efflux into the perfusate whereas the efflux of glutamic acid remained at a constant level. These findings strongly support the hypothesis that glycine is a transmitter in Ipc-tectal neurons.

Animals↗
PubMed1981

Serotonin and dopamine synthesis in phenylketonuria.

Two regulation systems of the serotonin and dopamine biosynthesis in patients with classical and atypical PKU were investigated. In classical PKU, the serotonin and dopamine biosynthesis is inhibited by high L-phenylalanine in blood and tissues. The dopamine formation in vivo was inhibited by phenylalanine blood concentrations higher than 25 mg/dl: the serotonin formation was inhibited even at a phenylalanine blood concentration of only 8 mg/dl. In two patients with dihydrobiopterin synthetase deficiency, the dopamine, and even more pronounced the serotonin, excretions are considerably reduced. The dopamine excretion was reduced to about 50% and the serotonin excretion to only 10% compared to controls. Under BH4 therapy (16 mg daily), the dopamine values increased about twice, serotonin threefold and the phenylalanine blood concentration normalized to 1-1.5 mg/dl. On loading a patient with BH2 synthetase deficiency with 50 mg/kg deuterated tryptophan-d5 and 150 mg/kg deuterated tyrosine d2 (phenylalanine blood concentration of 16 mg/dl), deuterated dopamine d1 and serotonin d4 could only be formed in detectable amounts after BH4 administration. During BH4 therapy the amount of dopamine d1 and serotonin d4 formed was lower than but comparable to normal controls.

Dopamine↗
PubMed1980

In vivo studies of the tryptophan-5-hydroxylase system. Quantitation of serotonin and tryptamine using gas chromatography-mass fragmentography.

An in vivo determination of tryptophan-5-hydroxylase (E.C. 1.14.16.4) activity is described. Subjects were loaded with deuterated L-tryptophan-d5 (50 mg/kg body weight) and the deuterated serotonin-d4 in urine was analysed using mass fragmentography. Four control subjects were dosed orally and two of them also intravenously with 50 mg/kg of L-tryptophan-d5. One patient with atypical phenylketonuria (PKU) due to a tetrahydrobiopterin (BH4) deficiency was dosed without and during BH4 treatment. Without BH4, the patient showed only minor formation of deuterated serotonin. After BH4 administration (2.5 mg/kg body weight) the serotonin formation increased about four-fold but was not normalized. Serotonin in urine and blood was analysed as the pentafluoropropionyl (PFP) derivative using gas chromatography-mass fragmentography. Deuterated serotonin was used as internal standard. The analysis of tryptamine can be performed with the same procedure.

Biopterins↗