Polymorphism of aspartic proteinases in resting and germinating barley seeds

Both resting and germinated barley seeds (Hordeum vulgare L. 'Morex') conta in aspartic endopeptidase activities, and the activities increase during ge rmination. We have extracted and partially purified aspartic endopeptidases from both resting seeds and green malt (four-day germinated barley). Six a spartic proteinase activities were found in resting barley seeds while only four activities were detected in green malt. All of the aspartic proteinas es had similar pH activity optima (pH 3.5-4.5) and pI values (approximate t o 4.5). The purified green malt aspartic proteinases selectively digested a group of barley seed proteins, postulated to serve as defensive proteins, that are coded by the amylase-trypsin inhibitor super gene family. The aspa rtic proteinases that bound to a pepstatin A affinity column at pH 4.5 cros sreacted with antiserum raised against aspartic proteinases purified from b arley seed. However, those that did not bind the affinity column also did n ot cross-react with the antiserum, indicating that there are two distinct g roups of aspartic proteases in germinating barley.