On the biological role of a proteolytic-enzyme inhibitor from the ectoparasitic tick Boophilus microplus

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Abstract
The tick B. microplus contains a protein that inhibits a range of proteolytic enzymes. Variations in the concentration of this protein throughout the life cycle were followed by measuring simultaneously the inhibition of trypsin and chymotrypsin and reaction with an antiserum to the purified inhibitor. The protein is present in large amounts in eggs and in unfed larvae, but its concentration falls very rapidly after the start of the parasitic stage of the life cycle. The inhibitor probably is important in eggs and in the initial establishment of the parasite on its host. The activity of the protein towards several enzymes was measured as an indication of its possible function. Bovine trypsin, chymotrypsin and plasmin and pig pancreatic kallikrein are all inhibited. The protein affects the blood-coagulation system at several points, since it prolongs both activated-partial-thromboplastin time and prothrombin time. It inhibits the complement-dependent lysis of erythrocytes, but is without significant effect on mitogen-induced lymphocyte stimulation. The inhibitor could have several effects on the host that would be beneficial to the parasite.