The next step of our study was to give a more detailed characterization of the interaction of thrombin with previous (due to their action) polyphenolic compounds. The BIAcore interaction analysis system may be used to examine the influence of the compounds on each other, i.e., on proteins, in terms of specificity

of a binding reaction, kinetics and affinity. BIAcore analysis system uses surface plasmon resonance (SPR) to monitor the interaction between Milciclib supplier molecules during the experiment time (Torreri et al., 2005). In our analysis, among the tested compounds the highest affinity to thrombin was presented by Epigenetics inhibitor cyanidin and quercetin (Table 2). These results are in agreement with BIAcore parameters obtained by Mozzicafreddo selleck inhibitor et al. (2006). They observed that quercetin has the lowest K D value, whereas K D for (−)-epicatechin was the highest. Similar parameters of silybin and (+)-catechin to association thrombin, despite their clearly distinct effect on the enzyme, are probably caused by the fact that, in BIAcore analysis, compounds bind to whole protein. When a ligand binds to the part of the protein which has no

effect on its function in BIAcore, we observe the same response as in the case of binding to the enzyme active center. This suggests that (+)-catechin probably bind also to other places of the enzyme. Cyanidin and quercetin, in BIAcore analyses, show the strongest affinity to thrombin, which is probably even stronger than the fibrinogen and PAR receptors affinity. Therefore, it explains the inhibition of thrombin proteolytic activity caused by these compounds. Only the partial inhibition of thrombin proteolytic activity by silybin can be explained by the fact that silybin affinity

to thrombin is higher than of cyanin, catechin or epicatechin, but lower in comparison to cyanidin and quercetin. for Analysis of graphs plotted by the Lineweaver–Burk linearization method (Lineweaver and Burk, 1934) (Fig. 5) demonstrated a competitive nature of human thrombin inhibition by using polyphenol aglycones. This means that these compounds mimic the structure of the substrate and reversibly interact with the free form of the enzyme in competition with the substrate for the enzyme active site. When the inhibitor occupies the active center of the enzyme, it prevents binding of the substrate and abolishes product generation. This inhibition may be reduced by adding more substrate to the reaction mixture (Bjelakovic et al., 2002). Our results obtained from Lineweaver–Burk curves confirm these assumptions (Table 3). Cyanidin, quercetin, silybin, (+)-catechin and (−)-epicatechin caused an increase of Michaelis constant value, while no effect on the maximum speed of reaction and on the enzyme catalytic constant was observed. Only in the case of cyanine we observed a mixed type of inhibition.