Cyclic dipeptides are widely used as models for larger peptides because of their simplicity and limited conformational freedom. Some cyclic dipeptides have been shown to be antiviral, antibiotic and anti-tumour. The aim of this study was to determine the biological activity of four cyclic dipeptides synthesized in this laboratory: cyclo(L-phenylalanyl-L-prolyl), cyclo(L-tyrosyl-L-prolyl), cyclo(L-tryptophanyl-L-prolyl) and cyclo(L-tryptophanyl-L-tryptophanyl). The enhancement or inhibition of calcium channels in ventricular myocytes from rats and delayed-rectifier potassium channels in ventricular myocytes from guinea-pigs were determined by use of the whole-cell patch-clamp technique. The induction of differentiation in HT-29 cells was assessed by assaying for an increase in the expression of alkaline phosphatase. Antibiotic properties against Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, Bacillus subtilus and Streptococcus sp. were determined by use of the Kirby-Bauer disc-diffusion assay. Results from these assays indicate that the cyclic dipeptides have biological activity in both prokaryotes and eukaryotes. Three of the dipeptides block cation channels in ventricular myocytes and all increase the expression of alkaline phosphatase. All the dipeptides have concentration-dependent antibacterial properties. These results suggest that with increased solubility the cyclic dipeptides might have potential as muscle relaxants, anti-tumour compounds and antibiotics.

Surimi seafood is a cooked gel product that utilizes fish protein from surimi to produce seafood analog products. Starch is the second most important ingredient used in the manufacture of surimi seafood due to its water holding ability and capacity to partially replace fish proteins while maintaining desired gel characteristics at a reduced cost. Typically, starch is added to surimi seafood formulations at 4-12%. Functional properties of surimi seafood to control wetness, stickiness, and/or thermal stability upon different storage and serving temperatures have been extensively studied using modified starches. There is a great need to review the role of starches in various applications of surimi seafood.

Studies have suggested a possible form of therapy based on the use of maturation-inducing compounds to induce differentiation of neoplastic cells and stimulate faster recovery of the normal cell population. The study of the effects of nine cyclic dipeptides on biochemical markers of differentiation implicated their potential to induce differentiation. Studies were undertaken to determine the specificity of these agents for HT-29 cell cultures as well as the identification of the signal transduction pathways affected by these agents inducing the differential gene expression observed in the cells. The cyclic dipeptides studied showed a high degree of specificity, having no significant effect on Caco-2 cells (P > 0.05), representing the normal gastrointestinal mucosa. All inducers administered were shown to affect the total energy state of HT-29 cells, an effect which increased the probability of HT-29 cell differentiation. Results indicated that those agents which induced differential gene expression acted at different steps in the isolated signal transduction pathway. Cyclo(Trp-Trp) and cyclo(Phe-Pro) induced a high degree of acetylation of histones (P < 0.05), while the remaining cyclic dipeptides induced a high degree of phosphorylation of histones (P < 0.05) (cyclo(Trp-Trp) induced a moderate degree of histone phosphorylation). The results from histone phosphorylation and acetylation and cyclic AMP responsive element binding protein phosphorylation studies suggest that the cyclic dipeptides activate a chromatin switch, which leads to the increase in accessibility of lineage-specific genes for transcription.

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