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United States Department of Agriculture

Agricultural Research Service

Title: Purification and Partial Characterization of Low Molecular Weight Barley and Malt Proteins That Inhibit Malt Endoproteinases

Authors
item Jones, Berne
item Marinac, Laurie

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 21, 1997
Publication Date: N/A

Technical Abstract: During malting and mashing, the barley storage proteins must be hydrolyzed into amino acids and low molecular weight (LMW) peptides. Nearly 50 endoproteinases occur in 4-day germinated barley and many of these are probably involved in hydrolyzing the storage proteins. The cysteine class endoproteinases are particularly important. We found that compounds in barley inhibited the activities of some of the endoproteinases. Since they could strongly affect malting quality, we have studied their biochemical characteristics. We have purified two LMW proteins that can inhibit the activity of a crude green malt enzyme extract. We have purified and partially characterized two barley seed proteinase inhibitors. One of them, Inhibitor 1 (I1), was identical with the product of a previously studied barley aleurone gene called Lipid Transfer Protein 2 (LTP2). The other inhibitor (I2) is a protein that was originally named Probable Amylase Proteinase Inhibitor (PAPI), but is now called LTP1. Both inhibitors specifically restrict the activities of green malt cysteine class endoproteinases. Because of the critical role the cysteine endoproteinases perform during malting, the inhibitors may have important roles in regulating protein degradation. It is not known whether the inhibitors are commingled with the cysteine proteinases in the germinating seed. If so, they could control their activities. Even if the inhibitors are spatially separated from the endoproteinases during malting, both the enzymes and inhibitors would dissolve into the wort during mashing, so they probably help regulate the protein solubilization that occurs during mashing.

Last Modified: 9/29/2014
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