Regulatory properties of phenylalanine, tyrosine and tryptophan hydroxylases.
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Amino Acids↗
Biomedical subjects
S Kaufman
Publications and source records attributed to S Kaufman.
Iron deficiency anemia among Jewish and Arab infants at 6 and 12 months of age in Hadera, Israel.
Infants attending six Family Health Centers of the Israel Ministry of Health in various Jewish and Arab localities in the Hadera subdistrict were examined for hemoglobin levels at 6 and 12 months of age. The prevalence of anemia (hemoglobin less than 11 g/dl) among Jewish infants rose from a total of 44.7 to 60% from 6 to 12 months. For the Arab infants, the prevalence of anemia increased from a total of 43.7% at 6 months to 71.0% at 12. The prevalence of severe anemia (less than 10 g/dl) for the Jewish infants rose from 4.5 to 13.1% and for the Arab infants from 7.7 to 19.6%. Of the Jewish infants with a hemoglobin level less than 10 g/dl at 6 months, 50% were still less than 10 g/dl at 12 months. Of the Arab infants less than 10 g/dl at 6 months, 36.4% were still at that level at 12 months. The lack of routine iron supplementation as a preventive procedure and the routine use of cow's milk for infant feeding are the probable causes of this high prevalence of iron deficiency anemia.
Anemia, Hypochromic↗
Congenital afibrinogenemia: an unusual case.
We describe a congenitally afibrinogenemic young man who experienced massive spontaneous bleeding episodes at unusual sites, including the thigh muscles, lung and brain. Each of these life-threatening episodes raised theoretical and critical practical problems. A large local hematoma was responsible for an accelerated consumption of fibrinogen, which was relieved following evacuation. It is unusual for an afibrinogenemic patient to survive a number of potentially lethal bleeding episodes.
Adult↗
The activation of rat liver phenylalanine hydroxylase by limited proteolysis, lysolecithin, and tocopherol phosphate. Changes in conformation and catalytic properties.
Pure phenylalanine hydroxylase from rat liver can be activated by limited proteolysis with alpha-chymotrypsin. As with most other types of activation of this enzyme, including activation by exposure to lysolecithin, the increase in activity is expressed in the presence of the naturally occurring pterin cofactor, tetrahydrobiopterin, but not in the presence of synthetic pterin cofactors such as 6-methyltetrahydropterin. With the chymotrypsin-activated enzyme, we have demonstrated directly, using circular dichroism measurements, that the activated enzyme differs in conformation from the native enzyme. In addition to chymotrypsin, trypsin and a mixture of rat liver lysosomal proteases can also activate phenylalanine hydroxylase. The latter finding raises the possibility that activation of the enzyme by limited proteolysis may be a physiologically important process. In experiments carried out with phenylalanine in which all five hydrogens on the aromatic ring have been replaced with deuterium, and in the presence of tetrahydrobiopterin, we have been unable to detect a kinetic isotope effect with either the native hydroxylase or with the hydroxylase activated by limited proteolysis, or by exposure to lysolecithin. By contrast, with both native and activated enzymes, a small isotope effect was detected when 6-methyltetrahydropterin was used as the pterin cofactor.
Animals↗
Spectroscopic investigation of ligand interaction with hepatic phenylalanine hydroxylase: evidence for a conformational change associated with activation.
We have examined the interaction of phenylalanine hydroxylase with phenylalanine, tetrahydropterin cofactors, and an activating phospholipid, lysophosphatidylcholine. Incubation of native phenylalanine hydroxylase with phenylalanine or lysophosphatidylcholine results in an increase in the fluorescence emission of the enzyme at 360 nm, which closely parallels the increase in tetrahydrobiopterin-dependent activity observed under these conditions. The presence of tetrahydrobiopterin in the absence of phenylalanine results in quenching of the enzyme fluorescence emission; this quenching exhibits a sharp end point at about 1 mol of tetrahydrobiopterin bound/mol of enzyme subunit. The binding of tetrahydrobiopterin under these conditions is unexpectedly tight, with an estimated KD of 10-20 nM, while in the presence of lysophosphatidylcholine, the KD is increased to about 25 microM. Quenching experiments with sodium iodide indicate greater exposure of tryptophan residues in the phenylalanine-activated enzyme. The ultraviolet difference spectrum of phenylalanine hydroxylase in the presence of phenylalanine exhibits a peak at 238 nm, which correlates with the fluorescence increase and activation, as well as additional changes in the aromatic region, which do not correlate well with activation. Phenylalanine does not alter the far-ultraviolet circular dichroism spectrum of phenylalanine hydroxylase. In contrast, lysophosphatidylcholine appears to induce a dramatic change in enzyme secondary structure upon activation. These results suggest that activation of phenylalanine hydroxylase results in a conformation change and the exposure of buried tryptophan(s) and possibly a cysteine residue.
Animals↗
Chondroitin sulfate in a new cornea preservation medium.
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Chondroitin↗
Ligand effects on the phosphorylation state of hepatic phenylalanine hydroxylase.
The effects of substrate and cofactors on the phosphorylation of hepatic phenylalanine hydroxylase by cAMP-dependent protein kinase and on dephosphorylation by phosphoprotein phosphatase have been examined. The presence of the natural cofactor (6R)-tetrahydrobiopterin strongly inhibits the activation observed under phosphorylating conditions; in contrast, this activation is enhanced approximately 20 to 50% by phenylalanine. The phosphorylation of the hydroxylase is strongly inhibited (approximately 80%) by (6R)-tetrahydrobiopterin, while phosphorylation is modestly stimulated by phenylalanine. High concentrations of phenylalanine (1 mM), however, can substantially reverse the inhibition of phosphorylation by (6R)-tetrahydrobiopterin. Neither (6R)-tetrahydrobiopterin nor phenylalanine affect the phosphorylation of a synthetic peptide substrate of cAMP-dependent protein kinase. The inhibition is specific for (6R)-tetrahydrobiopterin; the diastereoisomer (6S)-tetrahydrobiopterin has a much smaller effect, and 6-methyltetrahydropterin and 6,7-dimethyltetrahydropterin have no effect. Both phenylalanine and (6R)-tetrahydrobiopterin inhibit to a small extent the dephosphorylation of phosphorylated phenylalanine hydroxylase catalyzed by phosphoprotein phosphatase. Neither phenylalanine nor (6R)-tetrahydrobiopterin inhibit the dephosphorylation of phosphorylated histones by phosphoprotein phosphatase. These results suggest that the phosphorylation state, and thus the activation state, of phenylalanine hydroxylase in vivo may be modulated, in part, by the availability of substrate.
Animals↗
The interaction of aromatic amino acids with rat liver phenylalanine hydroxylase.
We have examined the interaction of hepatic phenylalanine hydroxylase with the phenylalanine analogs, tryptophan and the diastereomers of 3-phenylserine (beta-hydroxyphenylalanine). Both isomers of phenylserine are substrates for native phenylalanine hydroxylase at pH 6.8 and 25 degrees C, when activity is measured with the use of the dihydropteridine reductase assay coupled with NADH in the presence of the synthetic cofactor, 6-methyl-5,6,7,8-tetrahydropterin. However, while erythro-phenylserine exhibits simple Michaelis-Menten kinetics (Km = 1.2 mM, Vmax = 1.2 mumol/min X min) under these conditions, the threo isomer exhibits strong positive cooperativity (S0.5 = 4.8 mM Vmax = 1.4 mumol/min X mg, nH = 3). Tryptophan also exhibits cooperativity under these conditions (S0.5 = 5 mM, Vmax = 1 mumol/min X mg, nH = 3). The presence of 1 mM lysolecithin results in a hyperbolic response of phenylalanine hydroxylase to tryptophan (Km = 4 mM, Vmax = 1 mumol/min X mg) and threo-phenylserine (Km = 2 mM, Vmax = 1.4 mumol/min X mg). erythro-Phenylserine is a substrate for native phenylalanine hydroxylase in the presence of the natural cofactor, L-erythro-tetrahydrobiopterin (BH4) (Km = 2 mM, Vmax 0.05 mumol/min X mg, nH = 2). Preincubation of phenylalanine hydroxylase with erythro-phenylserine results in a 26-fold increase in activity upon subsequent assay with BH4 and erythro-phenylserine, and hyperbolic kinetic plots are observed. In contrast, both threo-phenylserine and tryptophan exhibit negligible activity in the presence of BH4 unless the enzyme has been activated. The product of the reaction of phenylalanine hydroxylase with either isomer of phenylserine was identified as the corresponding p-hydroxyphenylserine by reaction with sodium periodate and nitrosonaphthol. With erythro-phenylserine, the hydroxylation reaction is tightly coupled (i.e. 1 mol of hydroxyphenylserine is formed for every mole of tetrahydropterin cofactor consumed), while with threo-phenylserine and tryptophan the reaction is largely uncoupled (i.e. more cofactor consumed than product formed). Erythro-phenylserine is a good activator, when preincubated with phenylalanine hydroxylase (A0.5 = 0.2 mM), with a potency about one-third that of phenylalanine (A0.5 = 0.06 mM), while threo-phenylserine (A0.5 = 6 mM) and tryptophan (A0.5 approximately 10 mM) are very poor activators. Addition of 4 mM tryptophan or threo-phenylserine or 0.2 mM erythro-phenylserine to assay mixtures containing BH4 and phenylalanine results in a dramatic increase in the hydroxylation at low concentrations of phenylalanine.(ABSTRACT TRUNCATED AT 400 WORDS)
Amino Acids↗
[Leukocyte alkaline phosphatase in breast cancer].
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Alkaline Phosphatase↗
Sclerosing cholangitis. Anatomical distribution of obstructive lesions.
The cholangiograms of 36 patients with sclerosing cholangitis were reviewed. The mean age of the patient group was 43 years, and the mean disease duration was 4.5 years. Seventeen of the patients had associated inflammatory bowel disease. The mean serum bilirubin was 6.8 mg/dl, the mean SGOT was 105 IU/L, the mean SGPT was 108 IU/L, and the mean serum alkaline phosphatase was 534 IU/L. The cholangiograms demonstrated involvement of the extrahepatic bile ducts in 33 patients, involvement of the hepatic duct bifurcation in 33 patients, and involvement of the intrahepatic bile ducts in 35 patients. The cholangiograms were graded as to the areas of the most severe obstructive involvement. In 24 patients the area of most severe involvement was the hepatic duct bifurcation. In eight additional patients the hepatic duct bifurcation, along with the extrahepatic ducts and/or the intrahepatic ducts, were felt to be the areas most severely affected. This predilection for severe obstructive disease at the hepatic duct bifurcation in sclerosing cholangitis held for both patients with and without inflammatory bowel disease. Thus, most patients with sclerosing cholangitis have cholangiographic evidence of diffuse extrahepatic and intrahepatic biliary tract disease, with the hepatic duct bifurcation being the area generally most severely affected.
Adult↗
Role of right atrial receptors in the control of drinking in the rat.
Balloons were implanted at the junction of the superior vena cava and right atrium of the rat. Inflation of the balloon stretched the vein-atrial junction but did not cause a change in either arterial or central venous blood pressure. Inflating the balloon attenuated spontaneous night-time water intake and the drinking responses to 24 h water deprivation and subcutaneous (s.c.) isoprenaline (10 micrograms/kg body wt.). Water intake after I.P. hyperoncotic colloid (polyethylene glycol 20 M) was virtually abolished when the balloon was inflated immediately before giving access to water (4 h after injection). Inflating the balloon had no effect on drinking following I.V. hypertonic saline (5 ml 2M-NaCl/kg body wt.). These results support the hypothesis that volume receptors on the right side of the heart are involved in controlling water intake.
Animals↗
Effects of short term beta adrenoreceptor blockade on serum lipids and lipoproteins in patients with hypertension or coronary artery disease.
The effects of beta adrenoceptor blockade with propranolol or pindolol on serum total cholesterol, low density lipoprotein cholesterol (LDL), high density lipoprotein cholesterol (HDL), and its subfractions HDL2 and HDL3, serum triglyceride, and Intralipid clearance were studied in 17 normolipidaemic, non-diabetic patients with hypertension or angina pectoris. Both pindolol and propranolol had similar effects on fasting serum total and lipoprotein cholesterol concentrations. HDL2 cholesterol concentrations were reduced by 9 +/- 29% and HDL3 cholesterol increased by 11 +/- 16%, but there were no significant changes in total or LDL cholesterol in the combined groups after six weeks' treatment. After 12 weeks' treatment total cholesterol concentrations were reduced by 7 +/- 10% mainly owing to a reduction in the LDL fraction of 9 +/- 15%. Concentrations of HDL2 remained low, 8% less than control values. Serum triglyceride concentrations were increased by both drugs at six weeks but had returned to base values in the pindolol group by the twelfth week. Pindolol, but not propranolol, enhanced the rate of clearance of intravenous Intralipid.
Adult↗
Biopterin synthesis defect. Treatment with L-dopa and 5-hydroxytryptophan compared with therapy with a tetrahydropterin.
We have identified a generalized deficiency of monoamine neurotransmitters in a patient with a defect in biopterin synthesis. Neurotransmitter precursors (L-3,4-dihydroxyphenylalanine [L-dopa]; 5-hydroxytryptophan [5-HTP] and a tetrahydropterin [6-methyltetrahydropterin (6MPH4)] were investigated for their ability to normalize monoamine neurotransmitter metabolism. Before treatment, the concentrations of dopamine (DA), norepinephrine, epinephrine, and six monoamine metabolites were very low or undetectable in plasma, cerebrospinal fluid, or urine. L-Dopa and 5-HTP replacement was begun at age 7 mo. This therapy generally corrected the deficiency of monoamines and their metabolites, and improved neurological development until the age of 25 mo. Despite these benefits, the intermittent administration of L-dopa could not produce a stable improvement of acute neurological function or DA metabolism. In the 3 h after L-dopa administration, plasma DA and the motor activity and alertness of the patient rose and fell in parallel. Doses of L-dopa that were clinically optimal produced normal plasma levels of norepinephrine and epinephrine, but excessive concentrations of DA and its metabolites. Furthermore, the clinical and biochemical effects of L-dopa were inhibited by phenylalanine and 5-HTP, respectively, demonstrating that these amino acids have antagonistic pharmacological effects. Physiological correction of the monoamine deficit and the hyperphenylalaninemia of this disorder was attempted at age 35 mo using high doses (8-38 mg/kg per d) of 6MPH4. 6MPH4, a synthetic analogue of tetrahydrobiopterin, controlled the hyperphenylalaninemia. Significant concentrations of 6MPH4 were obtained in the cerebrospinal fluid; no neurological improvement or stimulation of monoamine synthesis in the central nervous system was detected. These findings indicate the complexity in replacement therapy with L-dopa and 5-HTP, but suggest that this treatment may be partially effective in biopterin-deficient patients who are unresponsive to high doses of tetrahydropterins.
5-Hydroxytryptophan↗
Biopterin synthesis defects: problems in diagnosis.
Hyperphenylalaninemia due to a biopterin synthesis defect was detected in an infant with decreased biopterin and increased neopterin levels in plasma and urine. Tetrahydrobiopterin (BH4) administration normalized plasma phenylalanine levels. CSF biopterin and neurotransmitter metabolite levels were normal and with the infant's normal growth and development suggest that the defect in biopterin synthesis did not affect CNS biopterin metabolism. Comparison of plasma and urine pterin levels from this patient with levels reported in patients who have neurologic complications fails to reveal differences that would distinguish patients at risk for neurologic problems. CSF pterin and neurotransmitter levels may correlate with neurologic function in these patients. CSF pterin and neurotransmitter determinations should be performed prior to initiation of neurotransmitter precursor and BH4 replacement therapies in patients who were determined to have biopterin synthesis defect(s).
Biopterins↗
The role of the heart in body fluid and electrolyte homeostasis.
Inflation of a balloon at the right superior vena caval/right atrial junction of the rat causes no change in arterial or venous blood pressure but does attenuate spontaneous night-time drinking and the acute responses to 24 h water deprivation and s.c. isoprenaline. Water intake after i.p. hyperoncotic colloid is virtually abolished whereas there is no effect on drinking to i.v. hypertonic saline or intracerebroventricular angiotensin II. Inflating the balloon also results in diuresis and natriuresis even in the conscious, renally denervated, Brattleboro' rat. Under these conditions the change in urine output cannot be explained by a fall in nervous input to the kidney, nor can it be caused by decreased ADH release since the Brattleboro' rat is totally deficient in ADH. Since there is no change in blood pressure, the diuresis and natriuresis must be mediated by some, as yet uncharacterized, hormonal factor. It is concluded that stimulation of the right atrial receptors resulting from increased venous return to the heart does play a role in controlling fluid intake and output and that this may be mediated at least in part, by a factor released from the heart itself.
Animals↗
Acquired arteriovenous fistula in a child with hemophilia.
A case of a 2 9/12-year-old hemophiliac boy who acquired an arteriovenous fistula in the right cubital fossa is described. This case shows the possibility that such fistulas can be iatrogenically induced in hemophiliac children subjected to repeated venipunctures.
Arteriovenous Fistula↗
Friendship, coping systems and community adjustment of mildly retarded adults.
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Adaptation, Psychological↗
Tetrahydro-sepiapterin is an intermediate in tetrahydrobiopterin biosynthesis.
7,8-Dihydrobiopterin is not an intermediate in the de novo biosynthesis of tetrahydrobiopterin, the cofactor required for aromatic amino acid hydroxylations. However, N-acetyl-serotonin inhibition of sepiapterin reductase, an enzyme whose previously only known function was the reduction of sepiapterin to 7,8-dihydrobiopterin, completely inhibited biosynthesis of tetrahydrobiopterin by bovine adrenal medulla extracts. We have now shown that sepiapterin reductase catalyzes the reduction of tetrahydro-sepiapterin to tetrahydrobiopterin and that this reaction is N-acetyl-serotonin-sensitive. A new pathway for tetrahydrobiopterin biosynthesis is proposed which takes these observations into account and which involves tetrahydro intermediates.
Adrenal Medulla↗