The partial purification and some properties of two sucrases of Phaseolus vulgaris

Abstract

Two sucrases present in P. vulgaris were easily differentiated, one, apparently specific for sucrose, with optimum pH 7.7 (named alkaline sucrase) and the other (shown to be a [beta]B-fructofuranosidase) with optimum pH 5.0. Alkaline sucrase was present in the ungerminated seed. [beta]B -Fructofuranosidase was absent from the ungerminated seed but appeared in the embryo on germination, reaching a maximum (under etiolated conditions) after 9-10 days. Much of the activity appeared in the roots. The alkaline sucrase could be purified only 2-fold, whereas the [beta]B-fructofuranosidase was purified 110-fold. The Km for the [beta]B-fructofuranosidase was 2.4 m[image] on sucrose and 14 m[image] on raffinose. Alkaline sucrase had Km 8.9 m[image] on sucrose. Both enzymes were inhibited by Ag+ ions (0.1 m[image]), though iodoacetamide (10 m[image]) had little effect. Alkaline sucrase was strongly inhibited by tris. Transferase activity was observed with the B-fructofuranosidase but not with alkaline sucrase. The function of the sucrases in vivo and their relation to the metabolism of raffinose-type oligosaccharides during germination is discussed.