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Biomedical subjects

J Burton

Publications and source records attributed to J Burton.

At least 19 recordsLinked to original sources
PubMed1992

Mapping the binding site of tissue kallikrein: preparation and testing of all possible substrate analog inhibitors homologous with the sequence of kininogen between Ser386 and Gln392.

Programs aimed at converting peptide inhibitors of proteolytic enzymes into more traditional drug structures require an understanding of the role played by the individual amino acid residues in the inhibitor. To this end, all possible substrate analogues occurring within the sequence Ser386-Pro-Phe-Arg-Ser-Val-Gln392 from bovine kininogen were synthesized and tested as inhibitors of tissue kallikrein (EC 3.4.21.35, beta-PPK). Of the 21 sequences which can be formed from the heptapeptide, 11 have inhibitory constants which could be measured in the chromogenic assay employed in these studies. No dipeptide and only one tripeptide, Ac-Phe-Arg-Ser-NH2 (Ki = 718 microM), measurably inhibits the enzyme. All longer peptides inhibit beta-PPK. The heptapeptide Ac-Ser-Pro-Phe-Arg-Ser-Val-Gln-NH2 is the most effective inhibitor in this series (Ki = 101 microM). Each amino acid residue in the sequence appears to alter binding in a relatively independent manner. The N-terminal seryl residue (P4) and the prolyl residue (P3) slightly improve the Ki of the various inhibitors. The phenylalanyl residue at P2 appears to have a more pronounced effect on Ki. The arginyl residue at P1 and the seryl residue at P1' appear to be the most important residues in the inhibitory sequence. They contribute approximately one-third and one-fourth of the binding energy to the interaction between the substrate analogues and beta-PPK, respectively. The valyl residue at P2', and the C-terminal glutaminyl residue improve Ki of each of the peptides tested. Almost 80% of the binding energy of the substrate analogue inhibitors comes from the core sequence Phe-Arg-Ser which occurs between P2 and P1'. Molecular models developed from the Chen-Bode coordinates of the aprotinin-beta-PPK complex have been used to interpret the results of these studies.

Amino Acid Sequence↗
PubMed1992

Studies on the design of orally active peptide analogues.

Converting peptide inhibitors of tissue kallikrein into drugs requires, among other things, that the compounds be made orally active. Measurement of the rate at which peptides diffuse across model epithelial membranes that mimic the human gut has allowed a quantitative relationship relating lipophilicity and % absorption to be developed. The absorption of simple peptides from the human gut may be predicted with this equation.

Administration, Oral↗
PubMed1992

A systematic approach for determining minimum inhibitory sequence and contribution of individual residues in binding of kininogen fragments to tissue kallikrein.

A systematic approach to evaluate the contribution of individual residues occurring within the sequence Ser386-Pro-Phe-Arg-Ser-Val-Gln392 from bovine kininogen towards binding to tissue kallikrein is developed. Of the 21 sequences which can be formed, no dipeptide and only one tripeptide measurably inhibits the enzyme. Almost 80% of the binding energy of the substrate analogue inhibitors comes from the core sequence Phe-Arg-Ser which occurs between P2 and P1'. Molecular models developed from the Chen-Bode coordinates of the aprotinin--beta-PPK complex have been used to interpret the results of these studies.

Amino Acid Sequence↗
PubMed1992

Activity distribution of seven digestive enzymes along small intestine in calves during development and weaning.

Ten groups of calves were used to study the changes in activity levels and distribution of seven hydrolases in the intestinal mucosa during development and weaning. The calves in the first group were sacrificed at birth while those in the remaining nine groups were either milk-fed until slaughter on days 2, 7, 28, 56, 70, and 119; or weaned between days 28 and 56 and then slaughtered on days 56, 70, and 119, respectively. The small intestine was immediately cut off and divided into five segments, ie, duodenum, proximal jejunum, median jejunum, distal jejunum, and ileum. In the milk-fed animals, the activity levels of aminopeptidases A and N, alkaline phosphatase, lactase, and isomaltase were maximum at 2 days of age, and then declined sharply between days 2 and 7 but did not change significantly thereafter. By contrast, the maltase activity increased between days 7 and 119, while no sucrase activity was detected. Weaning resulted in a decrease in the activity of lactase and an increase in that of aminopeptidase N, maltase, and isomaltase. The distribution of all these enzymes along the small intestine was slightly influenced by age but not at all by weaning.

Animals↗
PubMed1992

Plasma and tissue levels of digestive regulatory peptides during postnatal development and weaning in the calf.

Changes in the concentrations of cholecystokinin, gastric inhibitory peptide, gastrin, motilin, pancreatic polypeptide, secretin, somatostatin, and vasoactive intestinal peptide in calf plasma and antral, duodenal and/or pancreatic tissues were assessed by radioimmunoassay during postnatal development and after weaning in 50 male Holstein-Friesian calves (randomly distributed into 10 groups of 5 animals each). The calves in the first group were killed at birth while those in 6 other groups were colostrum-fed for 2 days and then milk-fed until 7, 28, 56, 70 or 119 days of age. Those in the remaining 3 groups were given the same diets until day 28, were then weaned between day 29-56, and slaughtered on days 56, 70 or 119. In milk-fed animals, changes in plasma and tissue concentrations of almost all digestive regulatory peptides were observed during the 1st month of postnatal life, especially at day 2. Weaning was accompanied by variations in the plasma concentrations of somatostatin, secretin, gastrin, pancreatic polypeptide and gastric inhibitory peptide but not by any apparent change in peptide tissue concentrations (except VIP in the duodenum). Thus, the variations in tissue concentrations are primarily age-related, while plasma concentrations were modified by age and weaning.

Aging↗
PubMed1992

Gastric and pancreatic enzyme activities and their relationship with some gut regulatory peptides during postnatal development and weaning in calves.

Changes in the activities of three gastric and nine pancreatic enzymes plus colipase were determined during postnatal development and weaning in calves. In calves exclusively milk-fed for 2, 7, 28, 56, 70 and 119 d, the enzyme activities per kilogram of empty live weight increased with age for chymotrypsin, elastase, carboxypeptidases A and B, ribonuclease and alpha-amylase, decreased for chymosin, lysozyme and colipase but showed no change in the case of pepsin, trypsin, lipase and phospholipase A2 compared with animals at birth. The greatest increase was that in alpha-amylase activity (about 50-fold between d 2 and 119). In calves weaned between d 28 and 56, all the activities were higher than in milk-fed animals, except that of chymosin (which was slightly lower) and that of colipase (which did not change). At 119 d of age, chymotrypsin, carboxypeptidase A, alpha-amylase and lipase were 1.6- to fourfold higher in ruminants than in preruminants. Thus, most enzyme activities were modified first by colostrum and milk intake, and again upon weaning by development of the forestomachs and ingestion of solid food. These ontogenic patterns might be under the control of many gut regulatory peptides, the plasma concentrations of which changed simultaneously. Some gastric and pancreatic enzymes were correlated to plasma concentrations of these gut regulatory peptides.

Abomasum↗
PubMed1992

Comparison of plasma prekallikrein levels in human skin blister and chamber fluids from volunteer subjects and psoriatic patients.

Suction blisters were successfully raised on lesional, perilesional and non-lesional skin of psoriatic patients. Similar blisters were created on the skin of volunteer subjects. A specific method has been established for the measurement of plasma prekallikrein, and validated for blister fluid, skin chamber fluid, plasma and synovial fluid. Combined levels of plasma prekallikrein and its active form were compared in blister fluids obtained from psoriatic patients and the volunteers. Significantly higher values for plasma prekallikrein were found in the non-lesional blister fluids of psoriatic patients when compared to the volunteer subjects.

Blister↗
PubMed1991

Three psychological treatments for bulimia nervosa. A comparative trial.

The specificity and magnitude of the effects of cognitive behavior therapy in the treatment of bulimia nervosa were evaluated. Seventy-five patients who met strict diagnostic criteria were treated with either cognitive behavior therapy, a simplified behavioral version of this treatment, or interpersonal psychotherapy. Assessment was by interview and self-report questionnaire, and many aspects of functioning were evaluated. All three treatments resulted in an improvement in the measures of the psychopathology. Cognitive behavior therapy was more effective than interpersonal psychotherapy in modifying the disturbed attitudes to shape and weight, extreme attempts to diet, and self-induced vomiting. Cognitive behavior therapy was more effective than behavior therapy in modifying the disturbed attitudes to shape and weight and extreme dieting, but it was equivalent in other respects. The findings suggest that cognitive behavior therapy, when applied to patients with bulimia nervosa, operates through mechanisms specific to this treatment and is more effective than both interpersonal psychotherapy and a simplified behavioral version of cognitive behavior therapy.

Adolescent↗
PubMed1991

Conformation and inhibitory properties of peptides based on the tissue kallikrein-aprotinin complex.

A series of peptides encompassing the primary binding segment (residues 12-19) of aprotinin has been synthesized and tested for their ability to inhibit porcine pancreatic kallikrein. A minimum sequence of five amino acids spanning residues 12-16 of aprotinin is necessary for inhibition of porcine pancreatic kallikrein. An octapeptide homologous with the binding segment of aprotinin has a Ki-value of 1.2 x 10(-4) M. The solution structure of the octapeptide was studied by one- and two-dimensional NMR methods for comparison with the known structure of the segment of aprotinin that contacts tissue kallikrein. NMR experiments suggest that the peptide is either a random coil or that it samples several conformations on the NMR time scale. Analysis of the molecular dynamics trajectory of the octapeptide also suggests that the peptide is highly flexible. Thus, inhibition by the octapeptide occurs because of its homology with residues 12-19 of aprotinin. Moreover, the absence of a stable solution conformation similar to that of the binding segment of aprotinin is consistent with the 150,000-fold increase in Ki of the octapeptide compared to intact aprotinin.

Amino Acid Sequence↗
PubMed1991

Synthetic peptide substrates for the immunoglobulin A1 protease from Neisseria gonorrhoeae (type 2).

Neisseria gonorrhoeae secretes protease which inactive human immunoglobulin A1 (IgA1) by cleavage of specific peptide bonds in the hinge region. The type 2 IgA1 protease (EC 3.4.24.13) is secreted as a 169-kDa precursor which undergoes autoproteolysis at three sites (A, B, and C) to release the 106-kDa active form of the enzyme (J. Pohlner, R. Halter, K. Beyreuther, and T. F. Meyer. Nature [London] 325:458-462, 1987). Synthetic decapeptides consisting of five residues on each side of the three autoproteolytic cleavage sites and their potential pentapeptide catabolites were prepared by solid-phase synthesis. Cleavage of the decapeptides by the type 2 IgA1 protease from N. gonorrhoeae was monitored by high-performance liquid chromatography. Peptides homologous with the amino acid sequences around the B and C sites are cleaved by the IgA1 protease. Amino acid analysis and Edman degradation show that the cleavage products have both the composition and amino acid sequence which would be expected from cleavage at the predicted sites. Km values of 1.35 mM and 3.43 mM and kcat values of 280 pmol/h/U and 439 pmol/h/U for the site B and site C peptides, respectively, were determined. The catalytic efficiency (kcat/Km) for the synthetic substrates is about 10% of that reported for intact IgA1. Cleavage of the peptides is inhibited by IgA1 protease inhibitors such as the tetrapeptide substrate analog inhibitor HRP-48, human colostrum, and a peptide-boronate transition state inhibitor. An extract from an N. gonorrhoeae construct lacking active IgA1 protease failed to cleave the synthetic substrate, while an extract from the control construct which secretes active enzyme completely hydrolyzed the synthetic peptide. Neither the site A peptide nor synthetic decapeptides encompassing cleavage sites in the hinge region of IgA1 are hydrolyzed by IgA1 protease. These are the first synthetic substrates to be reported for any IgA1 protease.

Amino Acid Sequence↗
PubMed1990

Transactivation of the transforming growth factor beta 1 (TGF-beta 1) gene by human T lymphotropic virus type 1 tax: a potential mechanism for the increased production of TGF-beta 1 in adult T cell leukemia.

We examined the effect of the human T lymphotropic virus type 1 (HTLV-I) Tax gene product on the human transforming growth factor beta 1 (TGF-beta 1) promoter. Transfection of deleted constructs of the TGF-beta 1 promoter revealed regions homologous with AP-1 binding sites that were required for Tax-induced transactivation of the TGF-beta 1 promoter. In addition, we examined the expression and secretion of TGF-beta in fresh leukemic cells isolated from patients with adult T cell leukemia (ATL) and in HTLV-1-infected T cell lines. We report that fresh leukemic cells from ATL patients constitutively produce high levels of TGF-beta 1 mRNA and secrete TGF-beta 1 but not TGF-beta 2 into the culture medium. In addition, long-term ATL cell lines expressed significant amounts of TGF-beta 1 mRNA as well as detectable levels of TGF-beta 1 protein. These results suggest a role for Tax in the upregulation of TGF-beta 1 in HTLV-I-infected cells.

Cell Line↗
PubMed1990

Association of intercellular adhesion molecule 1 with the multichain high-affinity interleukin 2 receptor.

Previously, using flow cytometric resonance energy transfer and lateral diffusion measurements, we demonstrated that a 95-kDa protein identified by two monoclonal antibodies (OKT27 and OKT27b) interacts physically with the 55-kDa alpha protein of the high-affinity interleukin 2 (IL-2) receptor. In the present study, this 95-kDa protein (p95) was purified and amino acid sequence data were obtained that showed strong homology to the human intercellular adhesion molecule 1 (ICAM-1). The identity of the p95 protein with ICAM-1 was confirmed by sequential immunoprecipitations using OKT27 and an antibody, WEHI-CAM-1, that is directed toward ICAM-1. We confirmed the physical proximity of p95/ICAM-1 to the IL-2 receptor alpha subunit by demonstrating that radiolabeled IL-2 could be cross-linked to this protein expressed on activated T cells. In functional studies, the antibodies OKT27 and OKT27b inhibited T-cell proliferative responses to OKT3, to soluble antigen, and to heterologous cells (mixed lymphocyte reaction). However, these antibodies did not inhibit IL-2-induced proliferation of an IL-2-dependent T-cell line. Taken together with our previous observations, the present studies suggest that ICAM-1 is in proximity and interacts physically with the high-affinity IL-2 receptor. The association of ICAM-1 with the IL-2 receptor may facilitate the paracrine IL-2-mediated stimulation of T cells expressing IL-2 receptors by augmenting homotypic T-T-cell interaction, by receptor-directed focusing of IL-2 release by helper T cells, and by focusing IL-2 receptors of the physically linked cells to the site of lymphocyte function-associated antigen 1-ICAM-1-IL-2 receptor interaction.

Amino Acid Sequence↗
PubMed1990

Clinical efficacy of emergency bypass surgery for failed coronary angioplasty.

The clinical and angiographic variables of 26 coronary artery disease patients at the University of Alberta Hospitals requiring emergency coronary artery bypass grafting (CABG) for failed percutaneous transluminal coronary angioplasty (PTCA) were reviewed. Emergency CABG was judged necessary in 2% of 1300 consecutive patients undergoing PTCA. The most frequent indication for an emergency operation was dissection and acute closure of eccentric bend point target lesions associated with clinically severe, unremitting chest pain and ST-T abnormalities suggestive of impending myocardial infarction. The mortality rate for the combined procedures of failed PTCA and CABG was low (3.8%). The incidence of periprocedural infarction was high (61%); it was, however, associated with a benign clinical course and electrocardiographic evidence of significant reversibility of acute phase damage. Thus, overall, emergency CABG appears to be a clinically efficacious treatment for patients with threatened or impending infarction as a consequence of failed PTCA.

Aged↗