Three new members of the a-amylase/trypsin-inhibitor family of cereal endosperm have been isolated from rye. N-terminal amino acid sequence comparison revealed that two of the purified proteins were the rye homologues of the barley monomeric inhibitor (BMAI-1) previously described, while the other rye protein corresponded to one of the subunits of the barley and wheat heterotetrameric inhibitors. However, the inhibitory specificities (active against human salivary a-amylase), aggregative behaviours (mainly as dimeric forms) and IgE-binding capacities (not recognized by sera from allergic patients) of the rye inhibitors were clearly different from those of their wheat and barley counterparts. These results indicate that homologous inhibitors may have distinctive properties in different cereal species.Plant proteins that inhibit a-amylases and proteinases from pests and pathogens are receiving considerable attention because of their potential role and use in plant protection [ 1, 21. A further reason to study some of these proteins (i.e. those from cereal endosperm) comes from the recent finding that they are major allergens in the allergic diseases provoked by inhalation or ingestion of cereal flours [3, 41.An inhibitor family of animal a-amylases and of trypsin, which is particularly abundant in wheat and barley endosperm, is among those that have been more actively studied (see [5, 61 for reviews). About 20 different members of this protein family, all of them with molecular masses in the 12-16-kDa range, have been characterized in these cereal species. The inhibitors of animal a-amylases can be either monomeric, homodimeric or heterotetrameric (three different subunits with one of them present in two copies), while those active against trypsin so far described are monomeric proteins. Joint consideration of the amino acid sequence similarities, the inhibitory activities and the chromosomal location of their coding genes, allows us to classify the inhibitor subunits into different subfamilies. In Triticum and Hordeum all subunits belonging to the same subfamily have similar inhibitory specificities and aggregative properties [6]. It should be mentioned that some subfamilies include components isolated from both wheat and barley, whereas others are represented by inhibitors detected in only one of these cereals [6].Knowledge of this protein family in other plant species, even within the Triticeae tribe, is still very scarce. Thus in rye, and concerning components active towards animal aamylases, although there are a few reports on their detection [7, 81, only the N-terminal amino acid sequences of two inhibitors have been reported. One of them shows a high degree of sequence similarity with a subunit of wheat and barley tetrameric inhibitors [9], but its aggregative behaviour and inhibitory activity has not been established. The second one is closely related with the subfamily of wheat homodimeric inhibitors and shows very similar properties to its Triticum counterparts [lo].We report here the characterization o...