A corn trypsin inhibitor with antifungal act inhibits Aspergillus flavus alpha-amylase

In this study, we found that the inhibition of fungal growth in potato dext rose broth (PDB) medium by the 14-kDa corn trypsin inhibitor (TI) protein, previously found to be associated with host resistance to aflatoxin product ion and active against various fungi, was relieved when exogenous alpha-amy lase was added along with TI. No inhibitory effect of TI on fungal growth w as observed when Aspergillus flavus was grown on a medium containing either 5% glucose or 1% gelatin as a carbon source. Further investigation found t hat TI not only inhibited fungal production of extracellular alpha-amylase when A. flavus was grown in PDB medium containing TI at 100 mu g ml(-1) but also reduced the enzymatic activity of A. flavus alpha-amylase by 27%. At a higher concentration, however, TI stimulated the production of alpha-amyl ase. The effect of TI an the production of amyloglucosidase, another enzyme involved in starch metabolism by the fungus, was quite different. It stimu lated the production of this enzyme during the first 10 h at all concentrat ions studied. These studies suggest that the resistance of certain corn gen otypes to A. flavus infection may be partially due to the ability of TI to reduce the production of extracellular fungal alpha-amylase and its activit y, thereby limiting the availability of simple sugars for fungal growth. Ho wever, further investigation of the relationship between TI levels and fung al alpha-amylase expression in vivo is needed.