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PLANT PHYSIOLOGY , Vol 110, Issue 2 639-644, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Purification and Characterization of an Oat Fructan Exohydrolase That Preferentially Hydrolyzes [beta]-2,6-Fructans
C. A. Henson and D. P. Livingston III
United States Department of Agriculture, Agricultural Research Service (C.A.H., D.P.L)
Oat (Avena sativa cv Fulghum) fructan hydrolase was purified by ammonium
sulfate precipitation and anion-exchange, hydrophobic interaction, and
size-exclusion chromatography. The enzyme was purified to homogeneity as
determined by the presence of a single band (43 kD) on a silver-stained
sodium dodecyl sulfate-polyacrylamide gel. A mixture of [beta]-2,6-linked
fructan (neokestin) isolated from oat was used as the substrate to purify
fructan hydrolase. Neokestin and small degree of polymerization fructan
isomers were used to characterize the substrate specificity of the purified
enzyme. The purified fructan hydrolase catalyzed hydrolysis of the terminal
[beta]-2,6 linkage of 6G,6-kestotetraose 3.5 times more rapidly than it
hydrolyzed the terminal [beta]-2,6 linkage of 6G-kestotriose and
approximately 10 times faster than it hydrolyzed the terminal [beta]-2,1
linkage of chicory inulin. Sucrose and 1-kestose were not substrates. The
Km for neokestin ([beta]-2,6-linked fructans with a degree of
polymerization of 7-14) hydrolysis was 2.8% (w/v), and the Vmax was 0.041
[mu]mol min-1 mL-1. The Km for hydrolysis of 6G,6-kestotetraose was 5.6%
(w/v), and the Vmax was 0.138 [mu]mol min-1 mL-1. Catalysis was exolytic
and by multiple chain attack. Hydrolysis of neokestin was maximal at pH 4.5
to 5.0.
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