ISOLATION AND CHARACTERIZATION OF AMERICANIN, A SPECIFIC INHIBITOR OFTHROMBIN, FROM THE SALIVARY-GLANDS OF THE LONE STAR TICK AMBLYOMMA-AMERICANUM (L)

A thrombin (EC 3.4.21.5) inhibitor (americanin) was isolated from the salivary glands of the lone star tick Amblyomma americanum (L.) using reversed-phase chromatography and anion-exchange chromatography. Ameri canin did not inhibit any other protease tested, including factor Xa, plasmin, trypsin, chymotrypsin, elastase, papain, pepsin, and carboxyp eptidase. The inhibition of thrombin by americanin decreased dramatica lly with dilution of the reaction mixture including thrombin, its subs trate, and americanin. When thrombin assays were performed in the pres ence of americanin, the reaction curve showed a time-dependent inhibit ion. Significant inhibition was observed when americanin concentration was approximately equal to that of thrombin, with a K-i of 0.073 nM. The results suggest that americanin is a specific, reversible, competi tive, slow, tight-binding inhibitor of thrombin. (C) 1997 Academic Pre ss.