Author
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Jones, Berne |
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Marinac, Laurie |
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Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/28/1999 Publication Date: N/A Citation: N/A Interpretive Summary: Malt is used to make beer. To make good beer, the malt needs to contain a specific, intermediate concentration of amino acids and small peptides. These compounds are formed in the malt by enzymes (proteinases) that break down specific barley proteins. In order to get the right amounts of amino acids and peptides, the proteinases must function correctly. In todays most commonly grown malting barley varieties the proteinases break down the proteins too quickly, so that the resulting malts contain too much amino acid material. We need to figure out how we can make the proteinases function more slowly, to release lower amounts of amino acids. We showed earlier that there are small proteins (inhibitors) in barley and malt that can stop some of the proteinases from working. Increasing the amount of these inhibitors in barley should lead to varieties that will produce better malts. This paper reports how we purified, identified and characterized one of the barley inhibitors. Now that we know what the inhibitor is and how it works, this knowledge can be used to increase the amount of this inhibitor in future barleys. This should lead to improved barley lines that will form malt that is more perfectly suited for brewing. Technical Abstract: We have previously shown that ungerminated barley contains inhibitors that suppress the activities of green malt cysteine proteinases. This paper reports the purification and partial characterization of a second barley cysteine endoproteinase inhibitor, a protein called lipid transfer protein 2 (LTP2). The chromatographically purified inhibitor had a molecular mass of 7,164. The amino acid composition and sequence data from the purified inhibitor indicated that it was a protein whose gene, but not the protein itself, was isolated earlier from barley aleurone tissue. The purified protein inhibited the activities of electrophoretically separated green malt cysteine proteinases, but not of the serine- or metalloproteinases. The purified LTP2 inhibited the same proteases as the LTP1 that we characterized previously, but was present in the mature seed in much smaller amounts. Neither LTP1 nor LTP2 has been proven to transport lipids in vivo, and it seems possible that both serve to keep cysteine endoproteinases that are synthesized during barley seed development inactive until the plant needs them. The small amount of LTP2 in the seed made it impossible to determine whether it, like LTP1, is involved in beer foam formation. Because of its proteinase inhibiting ability and its resistance to heat inactivation, some of the LTP2 may persist in beer. |
