Bifunctional α-amylase/trypsin inhibitor activity previously ascribed to the 22 KDa TL protein, resided in a contaminant protein of 14 KDa

The previously reported inhibitory activity of a 22 KDa protease and α-amylase inhibitor extracted from maize seeds, was re-investigated in order to confirm or rectify its ability to inactivate protease and α-amylase activities. The same inhibition was detected when the 22 KDa protein was purified following the original methodology (Richardson et al. 1987). However, when a new ion-exchange chromatography step was introduced after the RP-HPLC, the apparently homogeneous 22 KDa protein was further resolved into five different fractions. Four of them corresponded to different isoforms of the 22 KDa protein, all of which lacked inhibitory activity. The other small band corresponded to a contaminant protein, which was identified as the 14 KDa α-amylase/trypsin inhibitor. This protein was responsible for the reported double inhibition (protease and α-amylase inhibition), previously assigned to the 22 KDa protein. With this result, it was then possible to settle the question concerning the ability of this 22 KDa protein to inhibit those enzymatic activities. Interestingly, the four isoforms of the 22 KDa protein fractions showed anti-fungal activity when tested in vitro. In summary, we suggest that both the PR-proteins, as well as the inhibitor's family classification, should now be corrected. Thus, the 22 KDa protein should no longer be considered as a member of either the protease or of the amylase inhibitor families. Similarly, the inhibitory activity assigned to the PR-proteins should no longer be considered.