Abstract
An enzyme from mature grape berries that hydrolyzes sucrose was purified 55-fold on a protein basis and 135-fold on a polysaccharide basis. The substrate specificity was consistent with that of a β-fructofuranosidase (β-D-fructofuranoside fructohydrolase, EC 3.2.1.26). At pH 4 for sucrose Km = 4 mM, relative maximum velocity = 100; for raffmose Km = 22 mM, relative maximum velocity = 47; and for methyl β-D-fructofuranoside Km = 167 mM, relative maximum velocity = 77. Maximum velocity for sucrose approaches a maximum at pH 2. Km changes continuously from 19 mM at pH 2 to 0.8 mM at pH 5.85. Purified grape β-fructofuranosidase is stable at 30° from pH 2 to pH 7. At 3° under toluene and at pH 4 it is stable for several weeks. At 85° inactivation is rapid and irreversible. Heavy-metal ions (especially Hg2+, Pb2+, UO22+, and Ag+) and aniline are inhibitors. Sumner's9 3,5-dinitrosalicylic acid reagent in conjunction with semiautomatic syringes was found to be a convenient assay procedure for large numbers of incubations.
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