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ARS Home » Midwest Area » Peoria, Illinois » National Center for Agricultural Utilization Research » Crop Bioprotection Research » Research » Publications at this Location » Publication #84858

Title: SOYBEAN LIPOXYGENASE IS ACTIVE ON NONAQUEOUS MEDIA AT LOW MOISTURES: A CONSTRAINT TO XEROPHILIC FUNGAL GROWTH?

Author
item Gardner, Harold
item Grove, Marilyn
item KELLER, NANCY

Submitted to: Aflatoxin Elimination Workshop Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 10/28/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Many studies have implicated secondary products of the lipoxygenase pathway as inhibitors of Aspergillus growth and aflatoxin production. More recently, Burow et al. (Molec. Plant- Microbe Interactions 10: 380-387 [1997]) have shown that the primary product of soybean lipoxygenase-1, 13S-hydroperoxy- 9Z,11E-octadecadienoic acid, suppressed growth of Aspergillus species and inhibited aflatoxin production at the gene level by suppressing the expression of a ketoreductase in the aflatoxin biosynthetic pathway. However, Aspergillus can grow on dry crop seeds equilibrated at relative humidities at about 85% or higher, implying that lipoxygenase activity may not occur in dry media. Since previous work has not convincingly demonstrated that lipoxygenase can catalyze fatty acid oxidation at low humidities, research was designed to answer this question. Soybean extracts (pH 7.5) and linoleate (pH 7.5) were mixed separately with cellulose and then dried overnight by vacuum desiccation. Four relative humidities ranging between 52% and 95% were tested. Controls were treated the same, except the soybean extracts were inactivated by heating prior to mixing with cellulose. Oxidation of linoleate occurred at all relative humidities compared to much lower values of the controls. That the oxidation was principally enzymatic was shown by chiral analysis of the linoleate hydroperoxides formed. The main product was 13S-hydroperoxy-9Z,11E- octadecadienoic acid, followed by significant percentage of 9S- hydroperoxy-10E,12Z-octadecadienoic acid.