Browsing by Subject "peptide"

The aim of the literature review was to research barley proteins, metal-catalyzed oxidation and subjects related to it, like antioxidants and oxidation reactions in beer. In addition ACE inhibition was looked into. The object of the experimental part was to find out if the proteins of a barley-based industrial side product can be modified by metal-catalyzed oxidation or enzymatic hydrolysis, and how these treatments affect the different proteins in the sample material. In addition, the possible ACE inhibition activity of the reaction products was determined. The sample material was a protein-rich side-product of barley starch production. Two protein fractions were extracted from the material; an alcohol soluble fraction and a reduced fraction. The modification of the proteins in the sample fractions by oxidation and hydrolysis was determined with gel electrophoresis and size exclusion chromatography. The ACE inhibitory activity of the small peptides from these reactions was determined with UV-VIS spectroscopy. Three protein groups were identified from the sample material; polymeric B hordein, monomeric B hordein and C hordein. Contrary to expectations metal-catalyzed oxidation did not break down any of the proteins in the sample; instead it aggregated the proteins into bigger units. The enzyme treatment hydrolyzed the proteins effectively. Small peptides from the enzyme hydrolysis had an ACE inhibition IC50 of 246 µg/ml, which is similar to gluten hydrolysates IC50 of 29 µg/ml. IC50 is the inhibitor concentration where 50% of enzyme activity is inhibited. Instead of breaking down the subject proteins metal-catalyzed oxidation aggregated them, and thus it could not be used to make ACE inhibitory peptides. Enzyme hydrolysis was found to be a valid method of inhibitor peptide production. The peptides produced had an ACE inhibition capacity similar to previously known ACE inhibitory food hydrolysates.

The human tissue kallikreins (KLKs) form a family of 15 closely related serine proteases (KLK1-15). KLK3 is better known as prostate specific antigen (PSA) and it is highly prostate-specific. Kallikreins are attracting increased attention due to their role as biomarkers for screening, diagnosis, and monitoring of various cancers. Although PSA is a very useful marker for prostate cancer in the blood, the expression level of PSA is higher in normal prostatic epithelium than in tumour tissue, and it is further reduced in poorly differentiated tumours. It has been postulated that PSA activators (stimulating compounds) could be beneficial for patients with prostate cancer. The development of peptides as clinically useful drugs is greatly limited by their poor in vivo stability and low bioavailability. As the problems in using peptides as drugs are mainly arising from the peptide backbone, the focus for synthesizing peptide mimicking compounds is on the peptide backbone and how to replace it. The aim of this work was to replace the central disulfide bridge in the most potent PSA activating peptide C-4 by a hydrocarbon linker that had been previously synthesized in the research group. Two strategies for synthesis of the pseudopeptides were applied: a) synthesis of all peptide bonds on solid support by tailoring the reactions for this particular peptide, and b) synthesis of a monocyclic pseudopeptide in solution that could be incorporated directly into the standard protocol of solid phase peptide synthesis. The first strategy (a) proved to be tedious and would have required a lot of optimization to be successful. The cleavage conditions of the orthogonal protecting groups were not directly compatible with synthesis on solid support. The second strategy (b) also proved to be tedious, epimerization at the histidine residue was very prone in the solution phase even with standard peptide coupling reagents. However, the possibility to monitor all steps of the synthesis and to purify intermediate products made this synthetic route more attractive for this type of pseudopetide. The work in this master thesis resulted in a useful strategy to synthesise the desired pseudopeptides.