Partial inactivation of microbial proteinases with soybean Kunitz and Bowman-Birk inhibitors

It was previously demonstrated that some plant inhibitors are able to inactivate the bacterial proteinase subtilisin; since information concerning the effect of plant inhibitors on other microbial proteinases remains limited, we decided to determine the activity of the soybean Kunitz and Bowman‐Birk inhibitors (KI and BBI, respectively) on 14 proteinases of fungal and bacterial origin. The results show that microbial proteinases are frequently inhibited by KI and BBI and that proteinases with the same EC number (eg subtilisin Carlsberg and subtilisin BPN') may equally give different responses to the inhibitors. In particular, all serine proteinases examined were affected by both KI and BBI while metalloproteinases were not. Inhibition was also achieved on a range of microbial proteinases for which the mechanistic class is yet to be established; the data suggest that they belong to the serine type. In one instance, activation instead of inhibition was noted.