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Biomedical subjects

A Wallace

Publications and source records attributed to A Wallace.

At least 91 records · Page 5Linked to original sources
PubMed1990

Use of fragments of hirudin to investigate thrombin-hirudin interaction.

Site-directed mutagenesis was used to create hirudin in which Asn52 was replaced by methionine. Cyanogen bromide cleavage at this unique methionine resulted in two fragments. These fragments have been used to study the kinetic mechanism of the inhibition of thrombin by hirudin and to identify areas of the two molecules which interact with each other. The binding of the C-terminal fragment (residues 53-65) to thrombin resulted in a decrease in the Michaelis constant for the substrate D-phenylalanylpipecolylarginyl-p-nitroanilide (DPhe-Pip-Arg-NH-Ph). The N-terminal fragment (residues 1-52) was a competitive inhibitor of thrombin. There was a small amount of cooperativity in the binding of the two fragments. Whereas hirudin and its C-terminal fragment protected alpha-thrombin against cleavage by trypsin, the N-terminal fragment did not. Hirudin and the N-terminal fragment completely prevented the cleavage of alpha-thrombin by pancreatic elastase while the C-terminal fragment afforded a lesser degree of protection. The results of these experiments with trypsin and elastase are discussed in terms of interaction areas on thrombin and hirudin.

Antithrombin III↗
PubMed1990

Cloning and expression of a Porphyromonas (Bacteroides) gingivalis protease gene in Escherichia coli.

A genomic library of Bacteroides gingivalis W83 chromosomal DNA was constructed in the Escherichia coli lambda (lambda) vector EMBL 4. Three recombinant lambda phages expressing a cloned protease were identified in the library. All three lambda phages contained cloned overlapping DNA fragments from the same region of the chromosome and encoded the same cloned protease. The cloned protease was expressed poorly using its own promoter in E. coli.

Bacteroides↗
PubMed1990

Biological characterization of Trypanosoma cruzi zymodemes: in vitro differentiation of epimastigotes and infectivity of culture metacyclic trypomastigotes to mice.

Thirty-one Trypanosoma cruzi isolates from Chile, Peru, and Bolivia were studied in their capacity to differentiate in vitro from epimastigotes to metacyclic trypomastigotes on TAU-3AAG medium. Zymodeme 1 parasites displayed the best level of differentiation, which ranges from 60 to 90% depending on the isolate. Zymodeme 2 parasites exhibited highly heterogenous differentiation rates. This differentiation method permits the obtention of large amounts of metacyclic trypomastigotes from zymodeme 1 parasites. Metacyclic trypomastigotes obtained in vitro were infective to nude Balb/c hybrid mice. Zymodeme 1 parasites produced high parasitemias in this murine model; in contrast, zymodeme 2 parasites displayed lower parasitemias. Of a total of 27 T. cruzi isolates, 20 proved to be infective to mice, 12 gave enough parasites for further studies, and 8 of these were used for biological characterization. Results are compared with the infective clone Dm28 and Tulahuén strains maintained since 1954 in mice.

Animals↗
PubMed1990

Trypanosoma cruzi: a possible control of transfusion-induced Chagas' disease by phenolic antioxidants.

The following phenolic antioxidant food additives were evaluated against Trypanosoma cruzi epimastigotes: BHT, BHA, gallic acid and its methyl, propyl, octyl, and lauryl esters, 2,4-di-tert-butyl-6-(4-methoxybenzyl)-phenol, 4,4'-isopropilidenediphenol, and protocatechuic acid and its ethyl ester. The inhibition of the respiration; the changes in motility, shape, and lysis of the parasites; and the human blood hemolysis caused by these chemicals were studied. Human blood samples experimentally contaminated with 2000 or 150,000 trypomastigotes per milliliter were freed of parasites after treatment for 24 hr at 4 degrees C with 5 or 10 mM BHT (2,6-di-tert-butyl-4-hydroxytoluene), respectively. Consequently, BHT and other phenolic compounds deserve further study to determine their role in preventing the transmission of Chagas' disease by blood transfusion.

Animals↗
PubMed1990

Racial differences in baseline cyclic adenosine monophosphate concentrations per million T-lymphocytes and protein concentrations.

beta-Adrenergic blockers are less efficacious as monotherapy for the treatment of hypertension in blacks as compared with whites. Because beta-adrenergic stimulation and blockade differ between racial groups, biochemical differences in the beta-adrenergic pathway may exist. It is the intent of this report to show underlying similarities and differences, at least in part, in the beta-adrenergic pathway (e.g., baseline cAMP and protein concentrations) using the T-lymphocyte as the model system. A total of 20 (n = 10 black, n = 10 white) normotensive male volunteers were recruited, begun on a low-sodium diet to normalize serum catecholamines, and blood was collected for lymphocyte beta-receptor isotherm binding experiments and cAMP determination. There were no differences in Bmax, sites per cell, or kd. Basal cAMP concentrations were significantly higher in the black group (16.0 +/- 9.8 pmol/10(6) cells) compared with the white group (7.0 +/- 1.8 pmol/10(6) cells) (p less than 0.05). Protein levels from the lymphocyte suspension were also higher in the black group (1,081.0 +/- 367.7 micrograms/ml) compared with the white group (766.8 +/- 220.4 micrograms/ml) (p less than 0.05). Normalization of cAMP for protein yielded 83.2 +/- 55.4 fmol/micrograms protein in the black group and 56.6 +/- 29.8 fmol/micrograms protein in the white group (p = 0.11). Altered protein levels may be a confounding variable in studies of this type. Further work is necessary to identify the nature and significance of this protein elevation, its relationship to the adenylate cyclase system in lymphocytes, and the source of the cAMP elevation noted herein.

Adrenergic beta-Antagonists↗
PubMed1989

Contribution of the N-terminal region of hirudin to its interaction with thrombin.

Hirudin is a 65-residue polypeptide that specifically inhibits thrombin by forming a tight, noncovalent complex with the enzyme. The role of the two amino-terminal valine residues and the N-terminal alpha-amino group of hirudin in the formation of the complex has been investigated by site-directed mutagenesis and chemical modification. Replacement of the two N-terminal valyl residues of recombinant hirudin by polar amino acids resulted in an increase in the inhibition constant (KI). In contrast, replacement of these residues by hydrophobic amino acids had little effect on the value for KI. These results demonstrated that the hydrophobic nature of the N-terminal residues of hirudin was important for its interaction with thrombin. Addition of a single amino acid to the N-terminus of hirudin resulted in a marked increase in the value of KI. A similar effect was observed when the positive charge of the alpha-amino group was removed by acetylation. In contrast, amidination of this group, which preserves the positive charge, resulted in a less pronounced increase in the value of KI. Thus, it appears that a positive charge immediately adjacent to the N-terminal hydrophobic residue is required for optimal binding to thrombin.

Amino Acid Sequence↗
PubMed1989

Effect of heparin on the glia-derived-nexin-thrombin interaction.

In order to determine the specificity of the interaction between thrombin and glia-derived nexin (GdN), the inactivation of proteolytically modified human thrombin species by GdN has been studied. The second-order rate constants for the inactivation of alpha-, beta T-, gamma T- and epsilon-thrombin by GdN were 1.41, 0.63, 0.33 and 1.91 microM-1.s-1 respectively. The kinetic properties of gdN were also investigated in the presence of different types of heparin, fractionated according to antithrombin III-binding affinity. Association rate constants of both gdN and antithrombin III with alpha-thrombin were obtained using unfractionated, low- and high-affinity heparin types. The different heparin types gave optimal rates of inhibition at similar heparin concentrations for both inhibitors. At optimal heparin concentrations, the rate of inactivation of alpha-thrombin by GdN was 0.5-1.2 nM-1.s-1, which suggests that, under these conditions, the interaction is diffusion-controlled.

Amyloid beta-Protein Precursor↗
PubMed1989

An active role for patients in stress management.

Stress can be extremely debilitating, but the constraints of general practice can make it difficult for GPs to treat it effectively. This article describes a nurse-run stress management regime.

Counseling↗
PubMed1988

Interaction of carotid chemoreceptor and baroreceptor reflexes in anesthetized dogs.

Interaction between baroreceptors and chemoreceptors during simultaneous activation of the reflexes was studied in eight pentobarbital sodium-anesthetized vagotomized dogs. The carotid sinus reflexogenic area was isolated and perfused at controlled carotid sinus pressure (CSP), PO2, and PCO2. Random combinations of CSP, PO2, and PCO2 were delivered to the carotid sinus. Results were analyzed by multiple linear regression. For the arterial pressure response, increasing CO2 resulted in an upward shift of the baroreceptor reflex response curve and an increased slope of the linear portion of the curve. The heart rate-CSP curve was also shifted upward by CO2, with the effect being greatest at high levels of CSP. The respiratory frequency-CO2 relationship had an increased slope and was shifted upward when CSP was decreased. The responses of tidal volume and ventilation (VE) depended on all three inputs. At any level of PO2, decreasing CSP resulted in a parallel shift of the VE-CO2 relationship. The results indicate that there is a significant interaction between chemoreceptor and baroreceptor reflex sensitivities.

Algorithms↗
PubMed1983

Occurrence of idiopathic, familial hyperchylomicronaemia in a cat.

Primary hyperlipoproteinaemia (hyperchylomicronaemia with slight very low density lipoprotein elevation) is described in two related male cats. Fasting hyperlipaemia, lipaemia retinalis and subcutaneous xanthomas were detected on clinical examination. In one cat lipoprotein lipase activity measured after heparin activation was significantly reduced compared to the response in a normal cat. The lipid and protein concentration in each of the lipoprotein classes and the lipoprotein distribution of the two hyperlipaemic cats, two normolipaemic relations and 16 normolipaemic adult cats were determined. Plasma cholesterol and triglyceride levels were elevated in the hyperlipaemic cats with the major proportion of triglyceride and cholesterol being present in chylomicrons whereas in normolipaemic cats the majority of triglyceride was contained in very low density lipoprotein. High density lipoprotein was the predominant lipid carrier in both the normolipaemic and the hyperlipaemic cats but the protein content in chylomicrons was elevated in the two affected cats. The lipoprotein distribution in normal cats in this study agrees with previously reported values. The hyperlipaemic cats showed many of the features of familial lipoprotein lipase deficiency (type I hyperlipoproteinaemia, exogenous chylomicronaemia) which is an inherited disease in man.

Animals↗
PubMed1981

Myocardial infarction in dogs, demonstrated by non-enhanced computed tomography.

The capability of non-enhanced and enhanced CT scanning of the heart without ECG gating to detect myocardial infarction in living dogs was explored. CT findings were correlated with those at post mortem. In large transmural infarctions, areas of lower attenuation were detected without contrast medium enhancement and appeared as defects when intravenous contrast medium was administered. The infarct size as estimated on each CT scan correlated closely with post mortem values.

Animals↗
PubMed1979

A field study of the stress response syndrome. Young women after hysterectomy.

The symptom pattern previously delineated as the stress response syndrome in a mental health setting was hypothesized to be useful in conceptualizing reactions to a traumatic event in a nonpsychiatric patient population. The experience of loss resulting from nonelective hysterectomy for benign disease in women of childbearing age was selected as a relevant field study model. Twenty-eight women were studied one year after hysterectomy, using extensive psychological interviewing by women clinicians and experiential rating scales. Twelve subjects had a mild stress response syndrome, and five subjects had a serious level of intrusive and avoidant symptoms. Increasing severity of response was associated with persisting child-wish, deterioration in sexual functioning, and change in self-concept. Women who did well postoperatively generally had no future wish for children and were actively committed to achievement outside of the home.

Adaptation, Psychological↗