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Biomedical subjects

S Kaufman

Publications and source records attributed to S Kaufman.

At least 415 records · Page 23Linked to original sources
PubMed1975

Phenylketonuria due to a deficiency of dihydropteridine reductase.

The onset of neurologic symptoms in a child who had markedly elevated blood phenylalanine levels during the first two weeks of life and who was promptly treated with a low phenylalanine diet, with excellent control of serum phenylalanine levels, suggested that this child had an unusual form of phenylketonuria. In assays of the components of the phenylalanine hydroxylating system (open liver biopsy at 14 months), the activity of phenylalanine hydroxylase was 20 per cent of the average normal adult value. By contrast, no dihydropteridine reductase activity was detected in the patient's liver, brain or cultured skin fibroblasts. Since dihydropteridine reductase is also essential for the biosynthesis of dopamine, norepinephrine, and serotonin, disturbed neurotransmitter function may be responsible for the patient's neurologic deterioration. On the basis of these results, assay of reductase in cultured skin fibroblasts may be advisable in the initial diagnosis of phenylketonuria.

Biopterins↗
PubMed1975

Studies on the phenylalanine hydroxylase system in liver slices.

A method was developed to study the unsupplemented phenylalanine hydroxylase system in rat liver slices. All of the components of the system--tetrahydrobiopterin, dihydropteridine reductase, and the hydroxylase itself--are present under conditions which should be representative of the actual physiological state of the animal. The properties of the system in liver slices have been compared to those of the purified enzyme in vitro. The three pterins, tetrahydrobiopterin, 6,7-dimethyltetrahydropterin, and 6-methyltetrahydropterin, all stimulate the hydroxylation of phenylalanine when added to the liver slice medium in the presence of a chemical reducing agent. The relative velocities found at 1 mM phenylalanine and saturating pterin concentrations are: tetrahydrobiopterin, 1; 6,7-dimethyltetrahydropterin, 2.5; 6-methyltetrahydropterin, 13. This ratio of activities is similar to that found for the purified, native phenylalanine hydroxylase and indicates that the enzyme in vivo is predominantly in the native form. Rats pretreated with 6-methyltetrahydropterin showed enhanced phenylalanine hydroxylase activity in liver slices demonstrating for the first time that an exogenous tetrahydropterin can interact with the phenylalanine hydroxylase system in vivo. This finding opens up the possibility of treating phenylketonurics who still possess some residual phenylalanine hydroxylase activity with a tetrahydropterin like 6-methyltetrahydropterin which can give a large increase in rate over that seen with the natural cofactor, tetrahydrobiopterin.

Animals↗
PubMed1975

Studies on the phenylalanine hydroxylase system in vivo. An in vivo assay based on the liberation of deuterium or tritium into the body water from ring-labeled L-phenylalanine.

The rate of release of deuterons into the body water from 2,3,4,5,6-pentadeutero-L-phenylalanine has been shown to be a valid measure of the activity of the phenylalanine hydroxylase system in vivo. At a dose of 0.5 g/kg, the rate of release of deuterons is linear for 60 to 90 min. Male rats, which had previously been shown to have 22 to 25% more phenylalanine hydroxylase activity in liver extracts than female rats, produced deuterons from deuterated phenylalanine at a rate 20 to 30% greater than female rats. p-Chlorophenylalanine, which irreversibly inhibits phenylalanine hydroxylase in vivo, caused a similar degree of inhibition of the rate of deuteron formation as was found when phenylalanine hydroxylase was measured in extracts from the same group of animals. Methotrexate, which inhibits the phenylalanine hydroxylase system by preventing regeneration of the tetrahydropteridine cofactor, caused parallel inhibition of the in vivo assay as well as when the conversion of phenylalanine to tyrosine was measured in liver slices. Randomly ring-tritiated phenylalanine can be used interchangeably with ring-deuterated phenylalanine if greater sensitivity is needed in the in vivo assay for phenylalanine hydroxylase. However, a dose of 20 to 30 muCi/kg is required. The in vivo deuterium release assay described in this paper should be useful in studying the physiological control of the phenylalanine hydroxylating system. It also may be of value in differentiating between individuals who are heterozygotes for phenylketonuria and those who are homozygotes for hyperphenylalaninemia.

Animals↗
PubMed1975

Tryptophan hydroxylase. Purification and some properties of the enzyme from rabbit hindbrain.

Tryptophan hydroxylase from rabbit hindbrain has been extensively purified. It is estimated that the enzyme is between 85 and 90% pure and has a molecular weight of 230, 000. Sodium dodecyl sulfate gel electrophoresis shows that the enzyme is composed of two subunits very close in molecular weight (57, 500 and 60, 900). The substrate specificity and the reaction stoichiometry catalyzed by the enzyme in the presence of 6, 7-dimethyltetrahydropterin, 6-methyltetrahydropterin, and tetrahydrobiopterin have been determined. The effect of some natural occurring phospholipids on the purified enzyme was investigated.

Animals↗
PubMed1975

Hepatic phenylalanine hydroxylase and PKU.

The conversion of phenylalanine to tyrosine in mammalian tissues is catalyzed by a complex enzyme system composed of several essential enzymes and cofactors. All of these components have been assayed in liver biopsy samples from patients with the classic form of PKU. They are all present except for phenylalanine hydroxylase, thus establishing this enzyme as the missing component. This conclusion has been confirmed in immunotitration experiments with a specific antiserum to phenylalanine hydroxylase. With the use of a highly sensitive assay for the hydroxylase, 0.27% of the normal activity of phenylalanine hydroxylase has been detected in a liver sample from a patient with classic PKU. There is some evidence that this low level of catalytic activity is due to the presence of a nutant form of the enzyme rather than to very low levels of the normal enzyme. These results rule out the possibility that clasic PKU is caused by a deletion mutation. The finding that the properties of the enzyme are different from the normal enzyme also suggests that the low hydroxylase activity in PKU is not caused by a regulatory hene mutation, but rather by a mutation in the gene that codes for the structure of the hydroxylase.

Animals↗
PubMed1975

Haemoglobin G-Szuhu, beta80 Asn-Lys, in the homozygous state in a patient with abetalipoproteinaemia.

An 11-year-old Jewish girl of Turkish extraction with abetalipoproteinaemia was found to be homozygous for haemoglobin Szuhu (beta80 Asn leads to Lys). Except for the abnormal haemoglobin, no other haematological or biochemical abnormalities were found in her consanguineous parents and one sister. In the propositus, erythrocyte morphology showed the acanthocytosis known to be in association with abetalipoproteinaemia. Increased autohaemolysis was also found, which reverted to normal after treatment with vitamin E. This case represents the first reported association of abetalipoproteinaemia with an abnormal haemoglobin, and the first homozygous Hb G-Szuhu.

Abetalipoproteinemia↗
PubMed1975

Phenylalanine hydroxylase activity in liver biopsies from hyperphenylalaninemia heterozygotes: deviation from proportionality with gene dosage.

Liver biopsy samples from the patients with hyperphenylalaninemia have an average of 5 percent of the normal hydroxylase activity. The parents of the patients have between 7.3 percent (excluding the value for one parent) and 10 percent of the normal hepatic hydroxylase activity. An explanation for these findings involves negative interallelic complementation, which involves protein-protein interaction between subunits in a multimeric enzyme. In support of this model is the evidence that rat liver phenylalanine hydroxylase is a multimeric protein composed of two electrophoretically distinguishable subunits.

Alleles↗