Characterization of homologous inhibitors of trypsin and α-amylase from seeds of rye (Secale cereale L.)

Inhibitors of trypsin (EC 3.4.21.4) and α-amylase (1,4-α-d-glucan glucanohydrolase, EC 3.2.1.1) were purified from seeds of rye and their complete and partial amino-acid sequences, respectively, were determined, in part by homology. The trypsin inhibitor was a single polypeptide chain of M_r 13 753. Both proteins exhibited sequence homology with a group of cereal seed proteins that include inhibitors of proteinases and α-amylase. The trypsin inhibitor was most closely related to the barley trypsin inhibitor (76% identify) and the α-amylase inhibitor to CMa of barley (also an inhibitor of α-amylase activity) and to CM1 and CM2 of wheat (no known inhibitory activity). Antisera raised against the two inhibitors did not cross-react, but the α-amulase inhibitor reacted with an antiserum raised against the 0.28 α-amylase inhibitor of wheat. The rye inhibitors had similar secondary structure contents with about 36-39% α-helix and 11-19% β-sheet. These are the first amino-acid sequence and conformation studies reported for enzyme inhibitors from rye.