No description available.

No description available.

The endogenous opioid system may be involved in the pathogenesis of arrhythmias and produce deleterious haemodynamic effects in patients with myocardial ischaemia and/or cardiac failure. Plasma concentrations of β-endorphin, a potent opioid peptide, were elevated in 31/42 patients with acute myocardial infarction, 3/18 with unstable angina, 3/34 with chronic heart failure, 8/28 with acute heart failure and 10/14 with cardiogenic shock. (Met)enkephalin levels were generally normal. There was no independent statistical relationship between β-endorphin concentrations after myocardial infarction and the incidence of cardiac arrhythmias. In isolated myocardium, the opioid antagonists naloxone and nalmafene, and morphine, an agonist, all produced Class III antiarrhythmic effects. Naloxone enhanced the reduction in maximum upstroke velocity produced by hyperkalaemia and post-repolarization refractoriness developed. During myocardial ischaemia the Class III effects of naloxone were gradually lost but both racemic naloxone (active at opioid receptors) and d-naloxone (inactive) reduced the rate of rise of extracellular potassium concentration and preserved resting membrane potential. The fall in maximum upstroke velocity during ischaemia was enhanced by both compounds suggesting an additional Class I effect. In human studies, despite employing high doses of naloxone, it was only possible to show a minor prolongation of repolarization. In patients with coronary heart disease, naloxone administered by both intracoronary and intravenous routes had no effect on coronary blood flow. In patients with heart failure naloxone had no significant effects on a range of haemodynamic parameters, exercise performance or levels of dyspnoea and fatigue.

No description available.

No description available.

No description available.

Host Defense Peptides (HDPs) are small, cationic and amphipathic molecules with inherent antimicrobial and immunomodular function. However their effects on blood-derived T cells is unknown and is the focus of this investigation. In this thesis, porcine peripheral blood mononuclear cells (PBMCs) were stimulated with bovine myeloid antimicrobial peptide (BMAP)-27, BMAP-28, Indolicidin (Indol), or HH2 in the presence and absence of Concanavalin A (ConA). It was observed that BMAP-27, BMAP-28, and Indol inhibited ConA-stimulated porcine PBMC proliferation. To ensure that the observed effect on cell proliferation was not simply due to a physical interaction between the peptide and ConA, addition of peptide and ConA was staggered. Porcine CD4+/CD8+ T cells were isolated from blood using magnetic activating cell sorting (MACS) and it was determined that BMAP-27 and BMAP-28 inhibited ConA-stimulated T cell proliferation. They did not promote T cell necrosis, but approximately 40 % of the activated T cells undergoes apoptosis in the presence of BMAP-27 and BMAP-28. The remaining 60 % of the T cells consumed very little ATP and showed an increase in expression of cytotoxic T lymphocyte antigen-4 (CTLA-4), indicating the induction of T cell anergy. The addition of exogenous IL-2 decreased the surface expression of CTLA-4 in ConA- activated CD4+ T cells and induced renewed CD4+/CD8+ T cell proliferation, an indicator that these cells underwent activation-induced anergy. Thus, we submit that BMAP-27 and BMAP-28 may play a role in returning the activated T cell population to a homeostatic state through induction of peripheral tolerance mechanisms.

The secondary structure of the 33 kDa manganese-stabilizing protein from Anacystis nidulans R2 was predicted using information from a family of homologous sequences and applying the algorithms of Williams et al. and Zvelebil et al. From the sequence conservation and the predicted secondary structure, nine functionally important domains were identified. Additional algorithms predicted potential antigenic determinants and a region that may serve to bind this polypeptide to the Photosystem II core complex. One of the functionally significant regions exhibits partial sequence similarity to the Mn-binding site of the bacterial superoxide dismutase and was targeted for site-directed mutagenesis. Two aspartic acid residues in this region, which may form carboxyl bridges to stabilize Mn ions, were subjected to saturation mutagenesis. A hybrid vector which affords temperature regulated expression of a cloned gene, was constructed to introduce the various forms of the mutated gene into the cyanobacterium, A. nidulans R2. Pools of Eschericia coli and A. nidulans cells harboring mutant polypeptides have been obtained. Some mutant cyanobacteria display altered pigmentation and differences in generation time dependent upon growth temperature suggesting a functionally significant residue has indeed been altered. Future studies will be concerned with the characterization of specific mutants in order to determine the relationship between the structure and function of this polypeptide. / Department of Biology

The thesis discusses the design of potential inhibitors of Angiotensin Converting Enzyme (ACE). The synthesis of pep tide inhibitors containing arginine and histidine-type residues is described. Successful incorporation of these residues during peptide synthesis requires the use of protecting groups on the side-chains* and new developments in this area are described. Ch. 1 reviews the currently available protecting groups for histidine. A methodology for regiospecific introduction of protecting groups of type ROCH₂-, via their corresponding chloromethyl ethers, is described. A convenient synthesis of these reagents (specifically t-Butoxymethylchloride, Dum-Cl and 2,4,6-TrimethyIbenzyloxymethyl- chloride, Tom-Cl) is given. Ch. 2 demonstrates that a knowledge of the location of histidine protecting groups has become mandatory, both in peptide synthesis and elsewhere. Two methods) a), nuclear Overhauser enhancement measurements and b), a procedure involving methylation, deprotection and amino-acid analysis are presented, which have allowed the differentiation of ? and ? derivatised histidines. Ch. 3 reviews the currently available protecting groups for arginine. Using 2-phenylethyIguanidine as a model for arginine, a number of haloacylguanidines and 5,5-disubstituted pyrimidinones wBe synthesised, and this chapter describes their structures, and the potential use of the corresponding reagents in protecting arginine during peptide synthesis. Ch. 4 describes the synthesis of his tidyIphenylalanylarginine and several variants on this structure. Biological data showing the level of inhibition both of A.C-E- and of Renal ^ndopeptidase by these compounds is presented. The syntheses also provide a further demonstration of the efficacy of the recently introduced benzyloxymethyI, (Bom)protecting group.

The role of the amino-acid histidine in biologically important molecules and the problems encountered in its incorporation whether in protected or unprotected form into peptides, and recent work¹ establishing the importance of the location of the im-protecting group -N(π) being desirable are reviewed in the introduction. In Chapter 1 the electrolytic deprotection of π-phenacyl-thyroliberin is described: it was found to produce a complex mixture. This and otherdifficulties encountered by co-workers led to the conclusion that π-phenacyl was unsuitable for general use as a histidine protecting group. In Chapter 2, the investigation of the 1,1,l-trichlorobut-2-enyl group for histidine protection is described. A model compound- NI(1,1,l-trichlorobut-2-enyl)imidazole-was prepared and subjected to screening tests. A number of undesirable side-reactions including cis-trans isomerisation of the double bond were observed indicating that this is not a practical blocking group. A novel strategy of histidine protection involving reducing the basicity of the imidazole ring by temporary substitution with electronwithdrawing groups is outlined in Chapter 3. A new synthesis of N(α) -protected diiodohistidine derivatives and tests demonstrating their stability to routine conditions encountered in peptide synthesis and deprotection by hydrogenolysis are described. A synthesis of thyroliberin indicated the potential of this strategy. In Chapter 4 preparations of the corresponding 2,5-dibromoderivatives are described, and a solid phase synthesis of glycyl- L-histidyl-L-phenylalanine and a classical synthesis of thyroliberin are outlined. It was found however that although diiodination inhibited racemisation and dibromination was even more effective that direct blockade of the N(π) was indispensable for its complete prohibition. A new optimised preparation for N(α) -t-butoxycarbonyl,N(π) - benzyloxymethyl-L-histidine² is described in Chapter 5, this being the first simple three-step synthesis of a N(π)-protected histidine derivative. In Chapter 6 the use of N(α)-t-butoxycarbonyl ,N(π)-benzyloxymethyl- L-histidine as a protected intermediate in a number of demanding exercises, including the solid phase synthesis of angiotensin II and a solution synthesis of a histidyl-tryptophan dipeptide are demonstrated. No problems due to the histidine derivatives were encountered. Methods of evaluating the degree of racemisation occurring in activated histidine derivatives are discussed in Chapter 7.