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M J Bennett

Publications and source records attributed to M J Bennett.

At least 145 records · Page 8Linked to original sources
PubMed1994

CCK-A-selective tetrapeptides containing lys(N epsilon)-amide residues: favorable in vivo and in vitro effects of N-methylation at the aspartyl residue.

Previous structure-activity studies on a series of CCK-A selective tetrapeptide agonists, typified by A-71623 (Boc-Trp-Lys(CONH-Ph-o-Me)-Asp-(N-Me)Phe-NH2), have shown that replacement of the Lys(N epsilon-carbamoyl) substituent with N epsilon-acyl substituents resulted in partial agonists with moderate to high affinities for the CCK-A receptor and that replacement of the C-terminal dipeptide with either (N-Me)Asp-Phe or (N-Me)Asp-(N-Me)Phe was highly favorable to in vitro and in vivo CCK activity. The present study demonstrates that although analogues in the epsilon-amide series that are N-methylated at the Phe position are weakly active or inactive in an in vivo rat appetite suppression assay, incorporation of (N-Me)Asp or (N-Me)Asp-(N-Me)Phe modifications in this series results in analogues with markedly improved in vivo activity. In in vitro assays, there is minimal effect of N-methylation pattern on binding affinity, whereas there is a trend toward improved functional activity in the phosphatidylinositol hydrolysis assay in analogues containing (N-Me)Asp.

Amino Acid Sequence↗
PubMed1994

Domain swapping: entangling alliances between proteins.

The comparison of monomeric and dimeric diphtheria toxin (DT) reveals a mode for protein association which we call domain swapping. The structure of dimeric DT has been extensively refined against data to 2.0-A resolution and a three-residue loop has been corrected as compared with our published 2.5-A-resolution structure. The monomeric DT structure has also been determined, at 2.3-A resolution. Monomeric DT is a Y-shaped molecule with three domains: catalytic (C), transmembrane (T), and receptor binding (R). Upon freezing in phosphate buffer, DT forms a long-lived, metastable dimer. The protein chain tracing discloses that upon dimerization an unprecedented conformational rearrangement occurs: the entire R domain from each molecule of the dimer is exchanged for the R domain from the other. This involves breaking the noncovalent interactions between the R domain and the C and T domains, rotating the R domain by 180 degrees with atomic movements up to 65 A, and re-forming the same noncovalent interactions between the R domain and the C and T domains of the other chain of the dimer. This conformational transition explains the long life and metastability of the DT dimer. Several other intertwined, dimeric protein structures satisfy our definition of domain swapping and suggest that domain swapping may be the molecular mechanism for evolution of these oligomers and possibly of oligomeric proteins in general.

Bacterial Proteins↗
PubMed1994

Tetrapeptide CCK agonists: structure-activity studies on modifications at the N-terminus.

We had reported earlier on a novel series of potent and selective tetrapeptide cholecystokinin-A (CCK-A) agonists of the general structure Boc-Trp-Lys[epsilon-Y]-Asp-N(R)PheNH2 [Y = amides, ureas; R = H, Me] that were potent anorectic agents in rats. In an effort to optimize the potency, selectivity, stability, and efficacy of our lead candidate A-71623 [R = Me, Y = o-tolylaminocarbonyl; Tac] toward development of a clinical candidate, we have explored a series of analogues in which the N-terminal Boc functionality was systematically replaced with various amides, ureas, carbamates, and sulfonamides of differing size, hydrophobicity, and stereoelectronic properties. In general, these analogues maintained good potency and selectivity for the CCK-A receptor (guinea pig pancreas), as well as potent anorectic activity in rats. Those analogues exhibiting equal or superior activity compared to A-71623 but differing physicochemical properties may represent superior drug candidates.

Amino Acid Sequence↗
PubMed1994

Refined structure of dimeric diphtheria toxin at 2.0 A resolution.

The refined structure of dimeric diphtheria toxin (DT) at 2.0 A resolution, based on 37,727 unique reflections (F > 1 sigma (F)), yields a final R factor of 19.5% with a model obeying standard geometry. The refined model consists of 523 amino acid residues, 1 molecule of the bound dinucleotide inhibitor adenylyl 3'-5' uridine 3' monophosphate (ApUp), and 405 well-ordered water molecules. The 2.0-A refined model reveals that the binding motif for ApUp includes residues in the catalytic and receptor-binding domains and is different from the Rossmann dinucleotide-binding fold. ApUp is bound in part by a long loop (residues 34-52) that crosses the active site. Several residues in the active site were previously identified as NAD-binding residues. Glu 148, previously identified as playing a catalytic role in ADP-ribosylation of elongation factor 2 by DT, is about 5 A from uracil in ApUp. The trigger for insertion of the transmembrane domain of DT into the endosomal membrane at low pH may involve 3 intradomain and 4 interdomain salt bridges that will be weakened at low pH by protonation of their acidic residues. The refined model also reveals that each molecule in dimeric DT has an "open" structure unlike most globular proteins, which we call an open monomer. Two open monomers interact by "domain swapping" to form a compact, globular dimeric DT structure. The possibility that the open monomer resembles a membrane insertion intermediate is discussed.

Amino Acid Sequence↗
PubMed1994

Refined structure of monomeric diphtheria toxin at 2.3 A resolution.

The structure of toxic monomeric diphtheria toxin (DT) was determined at 2.3 A resolution by molecular replacement based on the domain structures in dimeric DT and refined to an R factor of 20.7%. The model consists of 2 monomers in the asymmetric unit (1,046 amino acid residues), including 2 bound adenylyl 3'-5' uridine 3' monophosphate molecules and 396 water molecules. The structures of the 3 domains are virtually identical in monomeric and dimeric DT; however, monomeric DT is compact and globular as compared to the "open" monomer within dimeric DT (Bennett MJ, Choe S, Eisenberg D, 1994b, Protein Sci 3:0000-0000). Detailed differences between monomeric and dimeric DT are described, particularly (1) changes in main-chain conformations of 8 residues acting as a hinge to "open" or "close" the receptor-binding (R) domain, and (2) a possible receptor-docking site, a beta-hairpin loop protruding from the R domain containing residues that bind the cell-surface DT receptor. Based on the monomeric and dimeric DT crystal structures we have determined and the solution studies of others, we present a 5-step structure-based mechanism of intoxication: (1) proteolysis of a disulfide-linked surface loop (residues 186-201) between the catalytic (C) and transmembrane (T) domains; (2) binding of a beta-hairpin loop protruding from the R domain to the DT receptor, leading to receptor-mediated endocytosis; (3) low pH-triggered open monomer formation and exposure of apolar surfaces in the T domain, which insert into the endosomal membrane; (4) translocation of the C domain into the cytosol; and (5) catalysis by the C domain of ADP-ribosylation of elongation factor 2.

Amino Acid Sequence↗
PubMed1994

6-Methyluracil excretion in 2-methylacetoacetyl-CoA thiolase deficiency and in two children with an unexplained recurrent ketoacidaemia.

6-Methyluracil (6MU) has been identified in urine collected during acute illness in two children with beta-ketothiolase deficiency (approximately 1 mmol/L) and in two children with recurrent infection-related ketoacidaemia of unknown aetiology (levels of 6.3 and 7.1 mmol/mmol creatinine). Significant amounts of 6MU were not detected in children with fasting ketosis in whom a metabolic disorder was excluded (normal levels less than 25 mumol/mmol creatinine). We propose that the production of 6MU may be related to the accumulation of acetoacetyl-CoA and thus be a marker for disorders where this occurs.

Acetyl-CoA C-Acetyltransferase↗
PubMed1994

The enzymes of mitochondrial fatty acid oxidation.

Defects of mitochondrial fatty acid oxidation are recent additions to the catalogue of inherited metabolic diseases. This review focuses upon decent developments in our understanding of the basic biochemistry, clinical presentations and molecular genetics of fatty acid oxidation disorders, with an emphasis on the strategies being used to define new disorders.

Fatty Acids↗
PubMed1994

Metabolic disease and sudden, unexpected death in infancy.

The prevalence of metabolic disease in infants dying suddenly and unexpectedly is controversial. Most studies have centered on major pediatric institutes with appropriate facilities to study inherited metabolic disease. No studies have been reported from nonacademic centers. We have prospectively studied urine and blood organic and fatty acids from 58 consecutive infant deaths over a 1-year period in nonteaching hospital medical examiners' offices in the state of Illinois for evidence of metabolic disease. One infant was found to have medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, homozygous for the common A985G mutation. One had probable non-A985G MCAD deficiency based on the identification of cis-4-decenoic acid in blood and one had ethylmalonic-adipic aciduria. Thus, we found evidence that inherited metabolic defects are related to unexpected infant death in this population. These disorders are present in a significant minority of infants who probably would have been given the diagnosis of sudden infant death syndrome if they had not undergone metabolic evaluation. We recommend that all infants who have died suddenly and unexpectedly be regarded as high-risk candidates for metabolic disease and that all such deaths be appropriately investigated as part of the routine autopsy procedure.

Acyl-CoA Dehydrogenase↗
PubMed1994

Use of high-fat formula for premature infants with bronchopulmonary dysplasia: metabolic, pulmonary, and nutritional studies.

The use of dietary fat in preference to carbohydrate offers the theoretic advantage of diminishing carbon dioxide production and thus the respiratory quotient, which may be beneficial for babies with chronic lung disease. Ten premature infants (birth weight (mean +/- SEM), 1.13 +/- 0.12 kg; postnatal age, 9 +/- 1 weeks) with bronchopulmonary dysplasia were alternately fed a high-fat and a high-carbohydrate formula each for 1 week, in randomized order. Lower rates of carbon dioxide production (6.6 +/- 0.3 versus 7.4 +/- 0.4 ml/kg per minute; p < 0.05), and consequently lower respiratory quotients (0.80 +/- 0.02 versus 0.94 +/- 0.01 ml/kg per minute; p < 0.005), were observed during the administration of the high-fat formula. There were no significant differences in results of pulmonary function tests with the use of either formula. Both formulas were equally well tolerated and able to promote adequate growth and normal biochemical profiles. However, weight gain was significantly greater with the administration of the high-carbohydrate formula, possibly because of an increase in the accretion of body fat. We conclude that the short-term use of high-fat formula for infants with bronchopulmonary dysplasia decreases carbon dioxide production while maintaining adequate growth and nutritional status.

Bottle Feeding↗
PubMed1994

A new syndrome with ethylmalonic aciduria and normal fatty acid oxidation in fibroblasts.

We describe four Italian male infants with a novel clinical phenotype characterized by orthostatic acrocyanosis, relapsing petechiae, chronic diarrhea, progressive pyramidal signs, mental retardation, and brain magnetic resonance imaging abnormalities. The first symptoms appeared after the termination of breast-feeding and introduction of formula feeding. Marked persistent 2-ethylmalonic aciduria was associated with abnormal excretion of C4-C5(n-butyryl-, isobutyryl-, isovaleryl-, and 2-methylbutyryl-)acylglycines and acylcarnitines and with intermittent lactic acidosis. Short- and branched-chain plasma acylcarnitine levels were also elevated. 2-Ethylmalonic aciduria is generally regarded as being indicative of a defect in fatty acid oxidation. Extensive studies of cultured fibroblasts failed to reveal such a defect. The observation of intermittent urinary excretion of 2-ethylhydracrylic acid pointed to involvement of the isoleucine R pathway in ethylmalonate biosynthesis. This hypothesis was tentatively corroborated by the biochemical responses to an oral isoleucine challenge in two patients. However, fibroblast studies showed normal oxidation rates of (14C)isoleucine (ul), indicating that this is not a defect of isoleucine oxidation expressed in skin fibroblasts. In one of two patients tested, cytochrome c oxidase activity was partially reduced (45%) in cultured fibroblasts. This unique clinical and biochemical phenotype identifies a new metabolic encephalopathy of yet undetermined cause.

Acyl-CoA Dehydrogenase↗
PubMed1994

Juvenile neuronal ceroid-lipofuscinosis: developmental progress after supplementation with polyunsaturated fatty acids.

Six patients with juvenile neuronal ceroid-lipofuscinosis (NCL) who were demonstrated to have abnormally low levels of membrane phospholipids were treated by dietary supplementation with polyunsaturated fatty acids (PUFAs) for periods ranging from 4 years 10 months to 7 years 3 months. Annual evaluations of intelligence and fine motor ability were undertaken while on supplementation. Mental development remained stable in most subjects throughout this period; fine motor function and vision were stable in the two youngest subjects only. These data suggest that PUFA supplementation may arrest the natural course of juvenile NCL if treatment is started early. A larger, multicenter, controlled trial is warranted.

Adolescent↗
PubMed1994

Population screening for medium-chain acyl-CoA dehydrogenase deficiency: analysis of medium-chain fatty acids and acylglycines in blood spots.

We have developed methods for the measurement of the medium-chain fatty acids octanoate, decanoate and cis-4-decenoate and the acylglycines n-hexanoylglycine (HG) and 3-phenylpropionylglycine (PPG) in blood spots using gas chromatography and mass spectrometry. Normal ranges were obtained for octanoate and decanoate. HG, PPG and cis-4-decenoic acid were not detected in control blood spots. In blood spots from nine patients (including two newborn) with medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, all metabolites were present in elevated concentrations although PPG was close to the detection limits and there was overlap for octanoate and decanoate. The lack of detection of cis-4-decenoic acid and HG in controls suggests that these are the metabolites of choice for blood spot identification of infants with MCAD deficiency.

Acyl-CoA Dehydrogenase↗
PubMed1994

Are competing psychotherapists manageable?

Behavioral health care faces major overhauling. The twin objectives of improved access and greater efficiency require reorganization of the delivery system from a disjointed array of competitors to an integrated continuum of collaborators. Ironically, the motif for achieving such a change is that of competition. This article questions reform through market forces alone and suggests a guided five-step process: guaranteeing the right to necessary care, regionalizing resources under capped budgets, replacing fee-for-service reimbursement with prospective payment, aligning continuing education requirements with performance-defined gaps in knowledge, and funding professional retraining. Shared accountability is proposed as an alternative to the problematic ethic of competition.

Clinical Competence↗
PubMed1994

Tiglylglycine excreted in urine in disorders of isoleucine metabolism and the respiratory chain measured by stable isotope dilution GC-MS.

Tiglyglycine (TG), an intermediate product of the catabolism of isoleucine, is increased in the urine of patients with beta-ketothiolase deficiency or with disorders of propionate metabolism. It is also implicated as a useful diagnostic marker in disorders of the respiratory chain. We present a method for the synthesis of TG and tiglyl[13C, 15N]glycine and the development of a stable isotope dilution mass spectrometric assay for TG. We compare data from controls with that from subjects with beta-ketothiolase deficiency and propionyl-CoA carboxylase deficiency, and with six patients with enzyme-confirmed disorders of the respiratory chain. TG was increased in the urine from all of the patient groups. The increased TG excretion did not persist in one patient with a respiratory chain defect, which suggests that, in some patients, multiple sample analysis may be necessary to identify a respiratory chain defect. This is the first urinary compound to be implicated as a potential marker of disorders of the respiratory chain.

Acetyl-CoA C-Acyltransferase↗
PubMed1994

Detection of metabolic disorders among selectively screened people with idiopathic mental retardation.

Fifth-eight people receiving residential or other services for idiopathic mental retardation were evaluated for evidence of metabolic disease. Five (8%) demonstrated persistent urinary organic acid abnormalities on at least three occasions, which pointed towards specific genetic metabolic defects. Instigation of specific treatment programs may have improved the quality of life for one of these participants. Appropriate genetic counseling was provided but could have been instigated much earlier had these investigations been performed as part of a routine workup for idiopathic mental retardation. This pilot study suggests a need for evaluation of other similar populations with idiopathic mental retardation.

Adolescent↗
PubMed1993

A quality assurance program for the measurement of capillary blood cholesterol levels in private pediatric practices. The Children's Health Project.

OBJECTIVE: To develop an easy to use quality assurance program for the measurement of capillary blood cholesterol levels in private pediatric practices. The program needed to comply with the guidelines laid down by the National Cholesterol Education Program. DESIGN: Intervention study. SETTING: Nine private pediatric practices in and around northern Philadelphia, Pa. PARTICIPANTS: The analysts included clinic staff members with laboratory expertise ranging from none to some previous experience. None of the participants had previous experience with a quality assurance program. INTERVENTIONS: Progress was reported monthly to the Lipid Research Laboratory, Philadelphia, and action was taken to correct inaccuracies in bias or variance. MAIN OUTCOME MEASURE: Compliance with the analytical guidelines laid down by the National Cholesterol Education Program in that the coefficient of variation was no greater than 5% and the bias was no greater than +/- 5% in the first year of the study. RESULTS: Within the first year of the study, there were 152 monthly quality assurance returns for each of two lyophilized control materials. On four occasions the coefficient of variation was greater than 5% while the overall bias was within the desired +/- 5% on 143 (94%) of 152 occasions. After the first 3 months of the study, as user confidence increased, intervention by the Lipid Research Laboratory became minimal. The internal quality assurance was further evaluated by a successful performance in a quarterly external quality assurance program. CONCLUSIONS: It is possible to devise an easy to use quality assurance program for extra laboratory measurement of cholesterol levels in children, and, with minimal assistance, maintain acceptable standards of cholesterol analysis. The quality assurance improved following the first 3 months of training and education. Subsequent continuous quality improvement was maintained with minimal involvement of the specialist center. Should the controversial issue of private office measurement of blood cholesterol levels become universally acceptable, the implication from our study is that standards acceptable to the National Cholesterol Education Program and the Clinical Laboratory Improvement Amendments of 1988 are possible using a suitable quality assurance program.

Bias↗