Abstract
Summary Barley, Hordeum vulgare(L.) Morex, stem fructan exohydrolase (FEH) has been partially purified andcharacterized. The enzyme was purified 258-fold by salt precipitation, anion exchange chromatography, affinity chromatography, and size exclusion chromatography. FEH has an apparent molecular weight of 62,500, and has an acidic pH activity optimum (5.5-6.0) as expected for a vacuolar enzyme. Barley FEH hydrolyzes only plant fructans (barley, chicory, and dahlia) releasing a free fructose and an undegraded fructan polymer per cleavage. Bacterial levan, sucrose, and other carbohydrates tested were not hydrolyzed. Sulfhydryl reducing agents do not enhance activity, and iodoacetamide (5 μM and 100 μM) does not decrease activity, indicating that sulfhydryl groups are not required for hydrolysis. Barley FEH has an Arrhenius Ea of 8.8 kcal/mol; these data were linear from 5 to 40 °C. This indicates that low temperature induced increases in fructan content are not primarily due to direct temperature effects on fructan exohydrolase activity.
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