The interaction of alpha-thrombin with the hirudin (HV1) fragment N alpha-acetyl desulfo hirudin45-65 (P51) was investigated. Kinetic analysis revealed that P51 inhibits the proteolysis of a tripeptidyl substrate with Ki = 0.72 +/- 0.13 and 0.11 +/- 0.03 microM for bovine and human alpha-thrombins, respectively. The inhibition was partially competitive, affecting substrate binding to the enzyme...

The rate of formation of ribonuclease-S from ribonuclease A by the action of subtilisin was measured at pH 5.5 in the presence and absence of the strongly bound ribonuclease inhibitor, 2’-cytidylate. Presence of the inhibitor in the active center significantly reduced the rate of formation of ribonuclease-S. Since bond 20-21 (and, to a lesser extent, 21-22), the cleavage of which is responsible...