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  • Titill er á ensku The effects of selected proteinase inhibitors on the activity of subilases from psychrotrophic, mesophilic and thermophilic microorganisms
  • Bakkalár
  • Útdráttur er á ensku

    The interactions between proteases and protease inhibitors is an important part of maintaining balance in organisms, without inhibitors proteases would degrade various components and parts of the organism and cause damage and even death. These protease-protease inhibitor interactions are also good models for studying protein-protein interactions and therefore give clues to the characteristics of the chosen protein. In this study which is a part of a larger research project on temperature adaptation of subtilisin-like serine proteinases, or subtilases, three such homologous enzymes from the proteinase K family were studied with regard to inhibition effects by various inhibitors on their activities. The subtilases where a cold adapted protease from a psychrophilic bacterium of a Vibrio species (VPR), proteinase K from the mesophilic fungus Engyodontium album (PRK) and aqualysin I from the thermophilic bacterium Thermus aquaticus (AQUI). A comparative research was carried out on these proteases with respect to inhibition by nine different inhibitors. Based on the observed inhibitory pattern on the enzymes three of these inhibitors were selected for further measurements. These inhibitors were turkey ovomucoid trypsin inhibitor (TOM) and the two synthetic inhibitors, chymostatin (CHYS) and phenylmethylsulfonyl fluoride (PMSF). In order to determine difference in inhibition patterns, the kinetic rate constants were found from activity measurements of the enzymes in the absence and presence of the inhibitors. The hypothesis was that the cold adapted protease would be inhibited at the fastest rate as they have greater molecular flexibility and presumeably more accessibility of the active site residues. In fact the opposite was indeed observed as the observed inhibition rates were fastest in the case of the thermophilic AQUI. From the measurements done with PMSF against the subtilases it was determined that a possible governing factor causing the slower rate of inhibition of PRK and VPRΔC is the larger entropic contribution to the activation barrier for inhibition, most likely as the result of larger structural flexibility of these two subtilases in the uninhibited form compared to the thermophilic AQUI.

  • 14.6.2013

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