Protease inhibitor activity is associated to a basic chitinase from potatobut not to an acidic one

Several pathogenesis-related proteins, which are produced in plants submitt ed to stress, have been identified as chitinases. We have previously descri bed that a potato basic chitinase strongly inhibited the activity of an asp artic protease isolated from the same source. In this work, we have tested the activity of two potato chitinases as protease inhibitors. A basic chiti nase (ChiB) inhibited trypsin, chymotrypsin, subtilisin, proteinase K and a serine protease of Fusarium sp. An acidic one (ChiA) did not show inhibito ry activity. The kinetics of trypsin inhibition by ChiB revealed different patterns of inhibition with azocasein and BAPNA. Metal ions affected differ entially both activities, suggesting that ChiB is a bifunctional protein. T hese results and those reported by other authors suggest a new physiologica l role for pathogenesis-related proteins. However, results presented in thi s paper suggest that the protease inhibitor activity is not a general chara cteristic of potato chitinases.