The effect of prostacyclin (PGI2) on trypsin and proteinase K activity

The effect of prostacyclin on the activity of serin proteinases was investigated. Trypsin and proteinase K were used as representatives of this class of proteinases and their activities determined employing the corresponding substrates: N alpha -benzoyl-arginine-p-nitroanilide for trypsin and hemoglobin for proteinase K. The proteolytic activity of trypsin and proteinase K was shown to be markedly decreased in the presence of prostacyclin. Enzyme kinetics was analyzed by microcomputer software package EZ-FIT, and the following kinetic parameters were obtained for trypsin and proteinase K: Km = 1.404 +/- 0.128 and 1.39 +/- 0.12 mmol/L, V-max = 58.24 +/- 1.87 and 58.13 +/- 1.87 mmol/L, Ki(1) = 0.368 +/- 0.023 and 0.59 +/- 0.038 nmol/L, respectively. On the basis of Akaike's information criterion test for fitness evaluation prostacyclin exhibited noncompetitive model of inhibition for trypsin and uncompetitive model of inhibition for proteinase K.