The complete amino acid sequence of the α-amylase inhibitor I-2 from ragi seeds was determined by analysis of peptides derived from the protein by digestion with trypsin, chymotrypsin thermolysin and S. aureus V8 protease. The protein consists of a single polypeptide chain of 95 amino acids, with a high content of serine and alanine, and no methionine, phenylalanine, histidine or tryptophan. There is no sequence homology with the bifunctional α-amylase/trypsin inhibitor in the same seeds or with any of the α-amylase inhibitors from other plants. The sequence contains two regions of weakly repetitive internal homology. The predicted secondary structure of the inhibitor is notable for the absence of α-helix and its high content (50%) of β-turn.
