DEVELOPMENT OF PROTEOLYTIC ACTIVITIES DURING BARLEY MALTING AND THEIRLOCALIZATION IN THE GREEN MALT KERNEL

The water-insoluble storage proteins of barley seeds reside in the sta rchy endosperm tissue. This tissue, when expressed from germinating ba rley, has a pH of 4.8. The hydrolysis of storage proteins during germi nation (malting) occurs mainly in the endosperm, so proteinases that a re located in endosperm and are active at pH 4.8 are probably importan t to the storage protein hydrolytic process. This study reports our co ntinued investigations of the endoproteinases of germinating barley (H ordeum vulgare L., cv. Morex) with a two-dimensional gel separation me thod that uses isoelectric focusing (IEF) and non-denaturing polyacryl amide gel electrophoresis (PAGE) in gels containing incorporated subst rate protein. We identified the endoproteinases that were active at pH 4.8 and determined when they appeared during germination and where th ey were located in 4-day germinated barley (green malt). A total of ni ne cysteine, four aspartic, and two serine class proteolytic activitie s that were active at pH 4.8 were extracted from the endosperm tissue of green malt. It seems probable that some or all of these endosperm e ndoproteinases, especially proteinases C7, C8, C11, D3, E3 and E4, are the ones most intimately involved in hydrolyzing the storage proteins during malting. (C) 1995 Academic Press Limited