PubMed Health⌕ Search

Biomedical subjects

L J Elsas

Publications and source records attributed to L J Elsas.

At least 109 records · Page 6Linked to original sources
PubMed1984

Direct physical evidence for stabilization of branched-chain alpha-ketoacid dehydrogenase by thiamin pyrophosphate.

Branched-chain alpha-ketoacid dehydrogenase is a multienzyme complex composed of four subunits. The 46,500-dalton protein is a subunit of the decarboxylase component, which is selectively digested by chymotrypsin. Two peptides of apparent mol. wts. of 36,000 and 15,000 result with loss of enzyme activity. When the complex is saturated with thiamin pyrophosphate and ketoacid substrate, digestion by chymotrypsin does not occur. These data provide direct physical evidence for the stabilization of the complex by the presence of the vitamin B1-derived cofactor.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1982

Clofibric acid and phenylpyruvic acid as biochemical probes for studying soluble bovine liver branched chain ketoacid dehydrogenase.

Purified bovine liver branched chain ketoacid dehydrogenase is inhibited by its reaction products, NADH and the branched chain acyl-CoA thiol esters. This provides an immediate, short term regulation mechanism for this enzyme which commits leucine, isoleucine, and valine to the catabolic pathway. We find that clofibric acid (p-chlorophenoxymethylpropionic acid) and phenylpyruvate also specifically inhibit this multienzyme complex. Fifty percent inhibition occurs at 0.24 mM and 0.40 mM concentrations, respectively. Both compounds bind either free enzyme (E) or the enzyme-substrate (ES) complex to give an abortive enzyme-substrate-inhibitor (ESI) complex. Phenylpyruvate preferentially binds E (Ki = 48 microM) over ES (alpha Ki = 97 microM), while clofibric acid has a reverse preference, binding ES (alpha Ki = 48 microM) with more avidity than E (Ki = 142 microM). Amino acids like L-leucine, beta-leucine, and 2-aminonorbornyl-2-carboxylic acid do not inhibit this enzyme at concentrations as high as 10 mM. These biochemical probes will be useful for studying the catalytic site of this enzyme complex and the consequences of accumulated branched chain ketoacids and their amino acid precursors on muscle and liver metabolism when the dehydrogenase function is impaired.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1982

Zinc status and growth of children undergoing treatment for phenylketonuria.

Children with phenylketonuria (PKU) are treated with semi-synthetic diets restricted in phenylalanine. Low-phenylalanine or phenylalanine-free formulae provide the majority of protein and energy in the diet while phenylalanine requirements are met by low-protein natural foods. Because of the restriction of natural protein sources in this diet, the study assessed the zinc nutrition of 22 treated children with PKU (aged from 1 month to 8 1/2 years) and correlated linear growth with zinc status. The mean (+/- SE) plasma zinc concentration of the PKU population was 66.6 +/- 3.3 micrograms/dl. The mean (+/- SE) hair zinc concentration was 70.2 +/- 11.5 micrograms/g. The mean plasma and hair zinc concentrations of the PKU population were significantly different (p less than 0.05) when compared with mean (+/- SE) normal values of 84.2 +/- 2.9 micrograms/dl and 130.7 +/- 8.3 micrograms/g, respectively. The mean (+/- SD) dietary zinc intake of 10 PKU patients was 8.56 +/- 2.68 mg/day. No significant differences (p less than 0.123) were found when the mean zinc intake was compared with National Academy of Sciences Recommended Dietary Allowance for age of 10 mg/day. No significant correlations were found when plasma and hair zinc concentrations were plotted with height percentiles. Further studies are required to assess the effects of zinc supplementation and the bioavailability of zinc from low-phenylalanine diets.

Child↗
PubMed1982

Coordinated system for comprehensive newborn metabolic screening.

In September 1978 phenylketonuria (PKU) screening in the state of Georgia was expanded to include testing for five additional metabolic disorders. Our goal was to begin therapy within the first three weeks of an infant's life. During the first 22 months, 167,458 specimens were received; 151,250 from infants less than or equal to 1 week of age. During this period 157,893 live births were reported. More than 90% of 2,299 infants with abnormal screening results were retested. The number of cases and incidence of each disease detected were hyperphenylalaninemia, five (1/31,579); maple syrup urine disease, 0 (0/151,250); homocystinuria, one (1/151,250); galactosemia, two (1/63,352); transient tyrosinemia (greater than or equal to 12 mg/dl), 50 (1/3,158); primary congenital hypothyroidism, 17 (1/7,453); and thyroid binding globulin deficiency, ten (1/12,670). For eight children with either hyperphenylalaninemia, homocystinuria, or galactosemia, the average time for retrieval between the initial abnormal screening result ad the first follow-up test was 6.2 days (range three to ten days). Therapy was started by 9.9 days of age (range seven to 17). For the 17 children with congenital hypothyroidism, the retrieval time was 11.6 days (range three to 27) and treatment began by 21.3 days of age (range ten to 69 days).

Academic Medical Centers↗
PubMed1981

Emery-dreifuss humeroperoneal muscular dystrophy: an x-linked myopathy with unusual contractures and bradycardia.

Clinical, electromyographic, and muscle biopsy findings in the two largest known families with Emery-Dreifuss humeroperoneal muscular dystrophy indicate that this is an X-linked recessive muscle disease with stereotyped clinical manifestations but with variable pathological and electromyographic characteristics. Elbow contractures, involvement of humeral muscles, hyporeflexia, and abnormal electrocardiograms are present in our patients. The disorder is associated with a potentially lethal cardiac arrhythmia that should be managed by pacemaker insertion. The skeletal muscle disease is slowly progressive and is usually not life threatening. Muscle biopsy commonly shows type I fiber atrophy. Electromyography usually indicates myopathy, though the classic findings of myopathy may not be present in every muscle.

Adolescent↗
PubMed1980

Acceptance of amniocentesis by low-income patients in an urban hospital.

A study was made of increased accessibility of genetic services to low-income obstetric patients in Atlanta, Georgia. The proportion of black patients averaged 83%. Of 522 patients counseled from August, 1976, through 1978, 157 were offered amniocentesis, and 95 (61%) elected the procedure. For most of the patients (120, or 76%) who were eligible for amniocentesis, age (greater than or equal to 35 years at delivery) was an indication; and of these, only six (5%) had any prior knowledge of genetic risk. During the same time interval, 188 patients over 35 years of age who initiated prenatal care too late for prenatal diagnosis were counseled in the hospital after delivery; 101 (54%) indicated that they would have accepted amniocentesis. The conclusion was that (1) genetic services are acceptable to this socioeconomic group, and (2) accessibility and publicity are needed to promote utilization in this population.

Amniocentesis↗
PubMed1980

Application of benefit-to-cost analysis to an X-linked recessive cardiac and humeroperoneal neuromuscular disease.

Benefit-to-cost analysis (using standard economic methods) and the predictive tools of genetics are important in the assessment of genetic services for high burden, single gene disorders. We have studied 6 generations of a 167-member, stable, North Georgia kindred at risk for X-linked recessive humeroperoneal neuromuscular disease with cardiac conduction defects. This disorder began in affected males in the teen years, with total disability expected by the 3rd decade and death by age 50. Using known fecundity rates and Mendelian probabilities, 26.6 heterozygous females and 9.4 hemizygous affected males were expected in the currently developing generation. We compared the compensatory costs for families with affected males against costs of genetic intervention for this disorder. All costs and benefits were discounted to present values at 6% and 10% and a benefit-to-cost ratio was derived. At a 6% discount rate the benefit-to-cost ratio was 21 to 1 while at a 10% discount rate the benefit-to-cost ratio was 14 to 1. We conclude that although this is an unusual X-linked muscular dystrophy, it constitutes a prototypic public and private expense which is largely preventable. The method of cost accounting within pedigrees has wide applicability. The results reemphasize the economic benefit of comprehensive public health programs in genetics, particularly in areas with stable, high risk-populations.

Cost-Benefit Analysis↗
PubMed1980

Ouabain-resistant hyperpolarization induced by insulin in aggregates of embryonic heart cells.

Spheroidal aggregates formed from trypsin-dissociated 14-day embryonic chicken hearts after 48 hr of rotation on a gyratory shaker. Intracellularly recorded resting membrane potentials of aggregates bathed in 1.3 mM K+ balanced salt solution had a mean (+/- SD) of 64 +/- 4 mV. After a stable potential was achieved, addition of 1-100 nM sodium bovine insulin caused a slow hyperpolarization of up to 19 mV after 4-5 min, followed, in some cases, by a further, more rapid, shift to a potential near EK. Equivalent hyperpolarizations were observed when insulin was added in the presence of 10 mM ouabain, indicating that enhanced Na+,K+ pump activity was not responsible for the change in membrane potential. The concentration of insulin that produced half-maximal hyperpolarization (2 nM) corresponded to the association constant of a high-affinity insulin receptor, suggesting that binding to this class of receptors led to the change in membrane potential. Steady-state current-voltage curves from current clamp experiments suggested that insulin produced an increase in slope conductance at potentials near rest by inducing an outward current with an apparent potential negative to -90 mV.

Animals↗
PubMed1980

Evidence supporting a two-receptor model for insulin binding by cultured embryonic heart cells.

Curvilinear Scatchard plots for insulin binding by cultured embryonic heart cells at 15 C were interpreted assuming a two-receptor model (Santora II, A. C., F.B. Wheeler, R.L. DeHaan, and L.J. Elsas II, Endocrinology 104:1059, 1979). The present studies test this hypothesis further. Both 125I-labeled hormone binding and 2-methylamino-[1-14C]isobutyric acid ([14C]meAIB) transport were assayed at 24 C in identical buffers. Equilibrium chicken insulin-binding experiments yielded curvilinear Scatchard functions, consistent with binding to both high affinity, low capacity and low affinity, high capacity receptor sites at 24 C. Insulin-stimulated transport of the model amino acid [14C]meAIB (a specific alanine-preferring system substrate) paralleled the expected occupancy of the low affinity receptors. In competitive binding assays, the abilities of multiplication-stimulating activity (MSA), proinsulin, and insulin to compete for primarily high affinity insulin binding were compared with their abilities to stimulate transport. The relative potencies for binding competition with 34 pM chicken [125I]insulin were insulin greater than proinsulin greater than or equal to MSA (1:0,05:0.03). In contrast, the relative potencies for stimulating [14C]meAIB transport were MSA greater than insulin greater than proinsulin (3:1:0.28). Maximal stimulation of transport by insulin was not additive to that by MSA or proinsulin. The relative potency profile for binding competition with [125I]MSA was the same as that for stimulation of transport: MSA greater than insulin greater than proinsulin (2-3:1:0.2-0.3). Proinsulin, added in excess of insulin at a constant molar ratio, reduced low affinity insulin binding to a greater extent than it reduced high affinity insulin binding. Moreover, the extent of binding to each receptor was predicted from, and thus directly supported, our biological potency data, in which proinsulin was nearly one third as potent as insulin at the low affinity receptor yet possessed only 5% of insulin's potency at the high affinity receptor. The different relative affinity profiles suggest that these two receptors had binding site specificities for different portions of the insulin molecule. Each experiment with proinsulin and insulin in a constant molar ratio was carried out in parallel with an experiment in which insulin was the only unlabeled hormone. Analysis of the results from weighted nonlinear least squares regression fits of data to Michaelis-Menten equations showed that a two-receptor model was necessary to fit the data obtained with insulin as the only unlabeled hormone. Low affinity site binding parameters were also needed when data within each parallel experiment were pooled. The following kinetic experiments indicated the absence of enhanced dissociation of bound [125I]insulin by unlabeled insulin...

Aminoisobutyric Acids↗
PubMed1979

Purification and characterization of branched chain alpha-ketoacid dehydrogenase from bovine liver mitochondria.

Branched chain alpha-ketoacid dehydrogenase (EC 1.2.4.3(4)) was solubilized and purified from bovine liver mitochondria for the first time. Decarboxylation of alpha-ketoisovalerate, alpha-keto-beta-methylvalerate, and alpha-ketoisocaproate was catalyzed by this multienzyme complex and this activity was co-purified for each substrate. Three enzymatic functions were contained in the complex including decarboxylation of the above ketoacids, transacylation of their simple acid derivatives, and reduction of NAD+ as an overall reaction. Product stoichiometry of these three reactions was 1 CO2:1 acyl-CoA:1 NADH. Activity depended upon the addition of thiamin pyrophosphate, CoASH, and NAD+ which were dissociable cofactors. Physically, two active forms of the enzyme complex were found: a 275,000-dalton unit and a 2 x 10(6)-dalton component. Both showed a characteristic flavin spectra and catalyzed all functions of the complex, implying that 10 small units aggregated into the larger unit. The soluble complex as visualized by electron microscopy had a diameter ranging from 12 to 24 nm corresponding to a molecular weight of 2 x 10(6). The size of the native membrane-bound component remains to be determined.

Amino Acids, Branched-Chain↗
PubMed1979

Linkage analysis using heterozygote detection in phenylketonuria.

This linkage investigation was undertaken utilizing an improved method for phenylketonuria (PKU) heterozygote detection. This method is based on studies of semi-fasting, noon-time, blood specimens obtained from 85 obligate heterozgotes and 45 controls who were neither pregnant nor on birth control medication. The best separation between heterozygotes and normals was achieved with a discriminant function involving the logarithms of the serum concentrations of phenylalanine, tyrosine and tryptophan. The theoretical overlap area between the distributions of heterozygotes and controls, based on the above function, was between the distributions of heterozygotes and controls, based on the above function, was 3.75%. In 19 obligate heterozygotes and 13 controls who were either pregnant or on birth control medication, the best separation was achieved with a discriminant function involving the logarithms of the serum concentrations of phenylalanine and tyrosine. The theoretical overlap area was 8.23%. These equations identified heterozygotes with sufficient accuracy to permit efficient genetic linkage analysis. We were unable to demonstrate genetic linkage between the PKU locus and 15 common blood, serum, and urinary markers. All but loose linkage (theta greater than 0.3) was excluded for Rh, ABO, Gc, Kidd, and AP. Moderate linkage exclusion (theta less than 0.2) was shown for PGM, Duffy, Hp, MNS, HL--A, and Kell. Close linkage (theta less than 0.1) was excluded for Amy2, 6PGD, P, and ADA. We were unable to find linkage heterogeneity between the Amish and non-Amish populations.

Chromosome Mapping↗
PubMed1979

Relationship of insulin binding to amino acid transport by cultured 14-day embryonic chick heart cells.

The characteristics of insulin receptors were studied in cultured embryonic chick heart cells which demonstrated insulin-responsive amino acid transport. Binding of [125I]iodoinsulin was time dependent, reversible, saturable, species specific, and proportional to cell number. Optimum binding occurred at pH 7.8 in the presence of 0.1% bovine serum albumin. Curvilinear Scatchard plots were found for chicken and bovine insulin binding at 15 and 30 C. Equilibrium association constants (Kas) and maximum capacities were calculated based on a two-receptor model. When studied at 15 C, chicken insulin was bound with Kas of 5.0 and 0.026 nM-1 for the high and low affinity receptors, respectively. Bovine insulin bound with Kas of 2.1 and 0.03 nM-1. The binding capacities of 600 and 9000 molecules/cell for the high and low affinity receptors, respectively, were the same for both species of ligand. At 30 C, the Ka of the high affinity chicken insulin receptor interaction decreased to 1.6 nM-1, whereas the low affinity Ka was not changed. In competitive binding assays, chicken insulin was 4 and 250 times more potent than bovine and guinea pig insulin, respectively. Human GH and mouse epidermal growth factor did not compete with chicken insulin. Although mouse epidermal growth factor did not compete with insulin, it did stimulate 2-aminoisobutyric acid accumulation. The maximal stimulation by this hormone was less than and additive to that produced by the maximal stimulation of insulin. These data indicate that insulin and epidermal growth factor acted through different receptors to stimulate amino acid transport. When insulin-stimulated functional response was compared to calculated receptor occupancy in this two-receptor model, stimulation of amino acid transport paralleled occupancy of the low affinity receptor such that at half-maximal transport stimulation, approximately 50% of these receptors were occupied. Half-maximal stimulation of 2-aminoisobutyric acid transport occurred at 18- and 20-nM concentrations of bovine and chicken insulins, respectively. Guinea pig insulin failed to stimulate 2-aminoisobutyric acid uptake even at 350 nM. Both the affinity of binding in the low affinity class and the insulin concentration for half-maximal stimulation of 2-aminoisobutyric acid transport were independent of temperature in the temperature ranges studied. We conclude that 14-day embryonic chick heart cells possess at least two classes of receptors which bind insulin. Occupancy of the lower affinity class of insulin receptors correlates quantitatively with insulin stimulation of 2-aminoisobutyric acid transport.

Aminoisobutyric Acids↗