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Cereal Chem. 70:589-595   |  VIEW ARTICLE

Purification and Characterization of Lipoxygenase Isoenzymes in Germinating Barley.

G. Yang, P. B. Schwarz, and B. A. Vick. Copyright 1993 by the American Association of Cereal Chemists, Inc. 

Two lip oxygenase (LOX) isoenzymes were extracted from barley (Hordeum vulgare 'Robust') and purified by hydroxylapatite chromatography, yielding LOX-1 with a pI of 5.2 and LOX-2 with a pI of 6.7. LOX-1 and LOX-2 appear to be monomeric proteins of 90 and 95 kDa, respectively. LOX-1 converted linoleic and linolenic acids into mainly 9-hydroperoxides, whereas LOX-2 produced mainly 13-hydroperoxides. Linoleic acid was found to be the best substrate for both isoenzymes. Km values for this substrate were determined to be 1.3 X 10[-5] M for LOX-1 and 1.9 X 10[-5] M for LOX-2. LOX-2 can oxidize esterified derivatives of linoleic acid (methyl linoleate and trilinolein) more readily than LOX-1 can. LOX-2 also had more heat resistance and better stability than LOX-1 did. LOX-2 developed only after germination, and the activity of both LOX-1 and LOX-2 increased to a large extent during germination. LOX-1 was localized exclusively in the germ in sound barley. Upon germination, LOX-1 and LOX-2 developed in newly synthesized rootlet and acrospire tissue. The rootlets contained exclusively LOX-2, while the acrospire contained both isoenzymes.

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