Three different proteinase inhibitors purified from crayfish blood,
a 23 kDa inhibitor of subtilisin, a 155 kDa trypsin-inhibitor
(pacifastin) and an α2-macroglobulin were tested for
their inhibitory activities against extracellular proteinases from the
specialized
crayfish parasite Aphanomyces astaci, the saprotrophic A.
laevis and the plant parasitic A. chochlioides and A.
euteiches. All three crayfish
inhibitors were effective against extracellular proteinases from the
different Aphanomyces species when defined peptides were used
as
substrates for the proteinases. Proteolytic activities from
A. astaci against a complex substrate, casein were reduced by
any of the
three crayfish proteinase inhibitors tested. It is, therefore, possible
that these proteinase inhibitors may reduce the proteolytic
breakdown exerted by A. astaci proteinases during an infection.