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Biomedical subjects

S Kaufman

Publications and source records attributed to S Kaufman.

At least 253 records · Page 14Linked to original sources
PubMed1987

Two enzymatic methods for determination of the phosphate content of phosphoproteins.

Two new enzymatic methods are described for the determination of the amount of inorganic phosphate covalently bound to macromolecules. In the first method, the inorganic matter obtained after ashing is incubated with [1-14C] pyruvate in the presence of pyruvate oxidase and the enzymatically formed 14CO2 is collected. The other method uses glycogenolytic enzymes to generate NADH which is then measured fluorometrically. The use of these two phosphate-dependent enzymes allows the measurement of phosphate at up to 1000 times greater sensitivity than is obtainable with the phosphomolybdic acid method, thus permitting phosphate analyses to be performed on microgram quantities of proteins.

Molybdenum↗
PubMed1987

Folinic acid therapy in treatment of dihydropteridine reductase deficiency.

We gave folinic acid to three siblings, and to a fourth child, who have or had dihydropteridine reductase (DHPR) deficiency. The youngest began folinic acid therapy in addition to neurotransmitter precursors and a phenylalanine-restricted diet at age 2 months, and at 2 years of age has near normal development without evidence of neurologic impairment. His older brother began similar treatment at 5 1/2 months of age, when early neurologic findings were evident. At age 6 years his mental retardation and neurologic impairment are less severe than reported in most patients with DHPR deficiency. Little improvement occurred in their sister, who first received treatment at 2 years of age, when she already had severe neurologic impairment. An unrelated boy with profound neurologic impairment showed subtle signs of improvement after he began treatment with folinic acid alone at age 9 years. These results provide evidence that folinic acid is important in the treatment of DHPR deficiency and, if begun early in infancy, may prevent irreversible neurologic damage. The mechanism of folinic acid action in DHPR deficiency may be to increase indirectly the synthesis of 5-methyltetrahydrofolate.

5-Hydroxytryptophan↗
PubMed1987

Structure and expression of human dihydropteridine reductase.

Dihydropteridine reductase (DHPR; EC 1.6.99.7) catalyzes the NADH-mediated reduction of quinonoid dihydrobiopterin and is an essential component of the pterin-dependent aromatic amino acid hydroxylating systems. A cDNA for human DHPR was isolated from a human liver cDNA library in the vector lambda gt11 using a monospecific antibody against sheep DHPR. The nucleic acid sequence and amino acid sequence of human DHPR were determined from a full-length clone. A 112 amino acid sequence of sheep DHPR was obtained by sequencing purified sheep DHPR. This sequence is highly homologous to the predicted amino acid sequence of the human protein. Gene transfer of the recombinant human DHPR into COS cells leads to expression of DHPR enzymatic activity. These results indicate that the cDNA clone identified by antibody screening is an authentic and full-length cDNA for human DHPR.

Amino Acid Sequence↗
PubMed1987

Acute tumour lysis syndrome with extreme metabolic abnormalities.

Tumour lysis syndrome, manifested by various metabolic derangements, is a known complication after treatment of some lymphoid malignancies. A patient is reported with acute lymphocytic leukaemia who developed a tumour lysis syndrome following intensive chemotherapy. All the known complications of the syndrome were present in the most severe form--hyperuricaemia of 1.44 mmol/l, hyperphosphataemia of 7.7 mmol/l with acute oliguric renal failure and extreme hyperkalaemia of 9.8 mmol/l with electrocardiographic changes. This life-threatening condition did not respond to conservative measures and the patient recovered only after haemodialysis.

Adult↗
PubMed1987

Cerebrospinal fluid monoamines in Down's syndrome adults at different ages.

Markers of monoamine metabolism in lumbar cerebrospinal fluid (CSF) and plasma were determined in nine young, healthy adults with trisomy 21 Down's syndrome (DS), 21-34-years-old, and in three DS subjects over 45 years, two of whom were demented, as well as in two groups of age-matched controls. Test scores of general intelligence, visuospatial ability, visual discrimination and verbal intelligence were reduced significantly in the old as compared to the young DS subjects. Dementia in DS was evident from a history of mental deterioration, disorientation and hallucinations. In the young DS adults, as compared to the controls, CSF 5-HIAA and norepinephrine were significantly elevated but plasma levels were unchanged. HVA, MHPG and biopterin did not differ between the DS groups and age-matched controls, or with relation to age in the DS or control subjects. These results suggest an increased turnover of monoamines in young adults with DS but that alterations in monoamine metabolism are unrelated to the cognitive decline with age in DS.

Adult↗
PubMed1987

Influence of right atrial stretch on plasma renin activity in the conscious rat.

Rats were prepared with inflatable balloons at the superior vena cava - right atrium junction. After recovery 1 week later, when blood was taken from conscious, normovolaemic animals plasma renin activity was found not to be influenced by right atrial stretch. Plasma renin activity was then measured in rats in which an extracellular fluid deficit had been produced by peritoneal dialysis against a hyperoncotic, isotonic solution. Although basal plasma renin activity was elevated (6.8 +/- 0.9 from 1.5 +/- 0.2 ng X mL X h, n = 19), no depression was observed in the experimental group after 15 or 90 min of balloon inflation. In rats pretreated with isoprenaline (10 micrograms/kg body wt.) plasma renin activity was also increased over basal levels, but again balloon inflation caused no reduction in plasma renin activity. It would appear that right atrial stretch has little, if any, influence on renin release in the conscious rat.

Animals↗
PubMed1987

Atrial stretch-induced diuresis in Brattleboro rats.

Inflation of a balloon at the superior vena caval/right atrial junction of the conscious Brattleboro rat initiated a rapid and significant diuresis, natriuresis, and kaliuresis (urine volume increased from 20.8 +/- 0.8 to 28.5 +/- 1.3 ml/h, P less than 0.005; urine sodium increased from 2,417 +/- 115 to 3,510 +/- 230 mu eq/h, P less than 0.005; urine potassium increased from 351 +/- 52 to 478 +/- 58 mu eq/h, P less than 0.05; n = 6). Bilateral renal denervation did not significantly alter this response. Since the Brattleboro rat is totally deficient in antidiuretic hormone (ADH) and since inflation of the balloon causes no change in blood pressure, the reflex increase in urinary salt and water output must be mediated, at least in part by a blood-borne factor other than ADH.

Angioplasty, Balloon↗
PubMed1987

Cardiac control of salt appetite.

Inflation of a balloon for 2 h at the superior vena caval-right atrial junction of the rat reduced the salt intake of animals that had been sodium and water depleted by peritoneal dialysis with hyperoncotic colloid. After the balloons were deflated, the experimental group drank more than the control group so that the total sodium intake of the two groups was the same. Thus stimulated increased venous return to the heart attenuates salt appetite. Since this phenomenon might be secondary to a reflex reduction in plasma renin activity, the experiment was repeated using a model of salt appetite in which the renin-angiotensin system is known to be suppressed, namely the deoxycorticosterone acetate-treated rat. Salt intake was again significantly reduced by inflation of the right atrial balloon. It is concluded that pathways exist, independent of the renin-angiotensin system, whereby information obtained from the cardiac volume receptors regarding the state of filling of the vasculature may be used to regulate salt intake.

Animals↗
PubMed1987

Enzymology of the phenylalanine-hydroxylating system.

The phenylalanine-hydroxylating system consists of 3 essential components, phenylalanine hydroxylase (PAH), dihydropteridine reductase (DHPR) and the coenzyme, tetrahydrobiopterin (BH4). DHPR and BH4 are also essential components of the trosine- and tryptophan-hydroxylating systems. During the hydroxylation reaction, BH4 is converted to the quinonoid dihydrobiopterin. The reduction of this latter compound back to BH4 is catalyzed by the reductase in the presence of NADH. In addition to the classic form of phenylketonuria, which is caused by a lack of PAH, a form is caused by a lack of DHPR and another by a deficiency of BH4 caused by the lack of an enzyme involved in its de novo biosynthesis. Besides hyperphenylalaninemia, these variant forms are characterized by neurological deterioration.

Amino Acid Metabolism, Inborn Errors↗
PubMed1986

Purification and state of activation of rat kidney phenylalanine hydroxylase.

Phenylalanine hydroxylase, the enzyme that catalyzes the irreversible hydroxylation of phenylalanine to tyrosine, was purified from rat kidney with the use of phenyl-Sepharose, DEAE-Sephacel, and gel permeation high pressure liquid chromatography. Our most highly purified fractions had a specific activity in the presence of 6-methyltetrahydropterin, of 1.5 mumol of tyrosine formed/min/mg of protein, which is higher than has been reported hitherto. For the rat kidney enzyme, the ratio of specific activity in the presence of 6-methyltetrahydropterin to the specific activity in the presence of tetrahydrobiopterin (BH4) is 5. By contrast, this ratio for the unactivated rat liver hydroxylase is 80. These results indicate that the kidney enzyme is in a highly activated state. The rat kidney hydroxylase could not be further activated by any of the methods that stimulate the BH4-dependent activity of the rat liver enzyme. In addition, the kidney enzyme binds to phenyl-Sepharose without prior activation with phenylalanine. The phenylalanine saturation pattern with BH4 as a cofactor is hyperbolic with substrate inhibition at greater than 0.5 mM phenylalanine, a pattern that is characteristic of the activated liver hydroxylase. The molecular weight of the rat kidney enzyme as determined by gel permeation chromatography is 110,000, suggesting that the enzyme might be an activated dimer. We conclude, therefore, that phenylalanine hydroxylases from rat kidney and liver are in different states of activation and may be regulated in different ways.

Animals↗
PubMed1986

Evidence for transcription and potential translation of the human 1.9 kb HindIII repetitive element.

Recombinant cDNA clones corresponding to the human 1.9kb HindIII repetitive element have been isolated from a cDNA library of liver cytoplasmic polyadenylated RNA. These cDNAs share 95% homology with the reported genomic DNA sequence and a similar amount of homology at the amino acid level with putative coding sequences (see preceding article by Mottez et al). They were isolated as two of four false positives from a human cDNA library in lambda gt11 and were selected with an antibody to an unrelated enzyme. These results provide direct evidence that this repetitive element is transcribed to form poly(A)+ RNA which could be translatable. Also, these observations may add to our understanding of the sources of false positives which are frequently observed in screens of cDNA libraries with antibodies as probes.

Amino Acid Sequence↗
PubMed1986

Proteolytic modification of the amino-terminal and carboxyl-terminal regions of rat hepatic phenylalanine hydroxylase.

Activation of rat liver phenylalanine hydroxylase by limited proteolysis catalyzed by chymotrypsin was investigated with the use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high pressure gel filtration. Both activation and proteolysis were decreased by the addition of the natural cofactor, (6R)-tetrahydrobiopterin. From chymotryptic digests of the hydroxylase carried out in the presence and absence of (6R)-tetrahydrobiopterin, several different enzyme species were isolated by high pressure gel filtration. One species (subunit Mr = 47,000) with unchanged hydroxylase activity was isolated from the chymotryptic digest in the presence of (6R)-tetrahydrobiopterin; it was derived from the native enzyme (Mr = 52,000) by cleavage of the COOH-terminal Mr = 5,000 portion of the native enzyme. In the absence of (6R)-tetrahydrobiopterin, another species (subunit Mr = 36,000) was isolated. In addition to modification at the COOH-terminal end of the molecule, this species also had lost a Mr = 11,000 fragment from the NH2-terminal end of the hydroxylase. The Mr = 11,000 fragment was shown to include the phosphorylation site of the enzyme. This Mr = 36,000 species was 30-fold more active than the native phenylalanine hydroxylase when assayed in the presence of tetrahydrobiopterin. These results suggest that the regulatory domain that inhibits hydroxylase activity in the basal state may be located at the NH2 terminus of the phenylalanine hydroxylase subunit.

Animals↗