1. Soluble β-fructofuranosidases were purified 16-fold from French-bean-pod extracts and 35-fold from potato-tuber extracts. 2. The two enzymes had similar overall properties but differed from each other quantitatively in lability and reaction kinetics. 3. A non-diffusible inhibitor of β-fructofuranosidase was present in the potato-tuber extracts but was absent from the bean extracts. This non-competitive inhibitor was acid-labile. 4. The possible roles of imidazole, carboxyl and thiol groups in β-fructofuranosidase action are discussed, and the properties of the bean and potato enzymes are compared with published data for yeast, mould and grape-berry enzymes.
