Three recombinant serine proteinase inhibitors expressed from the coding region of the thrombin inhibitor dipetalogastin.

Dipetalogastin is a potent thrombin inhibitor from Dipetalogaster maximus. The cDNA of dipetalogastin codes for a large protein which consists of six Kazal-type domains. There are three tandem, homologous regions each including two domains. Three biologically active recombinant proteins rDI, rDII and rDIII each corresponding to one region of the dipetalogastin cDNA were expressed, purified and investigated with regard to their biological activities. rDI and rDII with molecular masses of 12,660 and 12,911 Da, respectively, proved to be potent thrombin inhibitors. The investigation of their influences on amidolytic activities of different serine proteases showed no inhibition of factor Xa (FXa) and alpha-chymotrypsin. At a large molar excess of rDI and rDII over the enzymes only low effects on the activities of trypsin and plasmin were observed. rDIII differs much from the both others. An inhibition of thrombin was found only at a molar excess of rDIII over the enzyme. Furthermore, an inhibition of trypsin and low effects on plasmin were detected at a molar excess of inhibitor over these enzymes. These results indicate that rDIII is active against thrombin, trypsin and plasmin, and finally possesses no specificity for only one serine proteinase.