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Polymorphism of Aspartic Proteinases in Resting and Germinating Barley Seeds

¹Dept. of Agronomy, University of Wisconsin, Madison, WI, 53706. Present address: Merck & Co., Rahway, NJ 07036. ²U.S. Department of Agriculture, Agricultural Research Service, Cereal Crops Research Unit, Madison, WI 53705-2334. Department of Agronomy, University of Wisconsin, Madison, WI 53706. Names are necessary to report factually on vailable data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. Corresponding author. Phone: 608/262-4478. Fax: 608/264-5528. E-mail: BLJONES@facstaff.wisc.edu

Both resting and germinated barley seeds (Hordeum vulgare L. ‘Morex’) contain aspartic endopeptidase activities, and the activities increase during germination. We have extracted and partially purified aspartic endopeptidases from both resting seeds and green malt (four-day germinated barley). Six aspartic proteinase activities were found in resting barley seeds while only four activities were detected in green malt. All of the aspartic proteinases had similar pH activity optima (pH 3.5–4.5) and pI values (≈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 aspartic proteinases that bound to a pepstatin A affinity column at pH 4.5 cross-reacted with antiserum raised against aspartic proteinases purified from barley seed. However, those that did not bind the affinity column also did not cross-react with the antiserum, indicating that there are two distinct groups of aspartic proteases in germinating barley.