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Dietary flavonoids as inhibitors of metallopeptidases of the M49 family

Metallopeptidases of the M49 family are proteolytic enzymes that contain highly conserved HEXXXH motif and whose catalytic activity depends on the zinc cation [1]. Dipeptidyl peptidase III (DPP III) is the best characterized member of this family with distribution detected in almost all forms of life. The physiological role of DPP III has not been precisely determined, however it is assumed that it is involved in intracellular protein catabolism, mammalian pain modulatory system, and in the defense against oxidative stress. Flavonoids belong to the group of polyphenolic compounds that are ubiquitous in plants. They are important component of human diet and seem to have various pharmacological actions [2]. In this study, we selected 15 dietary flavonoids belonging to four different structural subclasses to investigate their potential inhibitory activity (at the physiological concentration i.e., 100 μM) against human DPP III. Inhibition of DPP III activity was determined using the spectrophotometric method [3] with minor modifications. For that purpose, purified recombinant human DPP III was briefly preincubated with a flavonoid in buffered solution and the enzymatic reaction was started with a Arg-Arg β- naphthylamide as a substrate. After the incubation time the reaction was stopped and the absorbance at 530 nm was measured. The percentage of enzyme inhibition (% inh.) was calculated by comparing the enzymatic activity without (normal activity) and with a flavonoid (inhibited activity). The results, obtained by in vitro assay showed that all analyzed dietary flavonoids have inhibitory effect against human DPP III hydrolytic activity at given concentration. The strongest inhibition (% inh. > 90) has been obtained with galangin, genistein, fisetin, kaempferol, and luteolin. A slightly lower inhibition (% inh. 50-90) has been observed for 3, 6- dihydroxyflavone, 3, 7- dihydroxyflavone, 6- hydroxyflavone, apigenin, morin and quercetin, while 3-hydroxyflavone, chrysin, flavone and flavanone have shown an inhibition of less than 50%. These data indicate that the presence and exact distribution of different structural groups on dietary flavonoids are important for their inhibitory properties. [1] N. D. Rawlings, F. R. Morton, C. Y. Kok, J. Kong, and A. J. Barrett Nucleic Acids Res 36 (2008) D320– D325. [2] S. Kumar, A. K. Pandey, Sci. World J. (2013) 162750. [3] M. Abramić, M. Zubanović, Lj. Vitale, Biol. Chem. Hoppe-Seyler 369 (1988) 29–38.

dietary flavonoid ; metallopeptidase ; inhibitor ; dipeptidyl peptidase III

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