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Articles

Legume

-GALACTOSIDASE FORMS DEVOID OF HEMAGGLUTININ ACTIVITY

Department of Biochemistry, University of California, Riverside, California 92521

Twenty different legume species (20 genera) were examined for -galactosidase and hemagglutinin activities. Although all of the species contained enzyme activity, only 13 of 20 contained hemagglutinin activities and none displayed a hemagglutinin activity comparable to the previously described -galactosidase-hemagglutinins.

The -galactosidase activities in the 20 species possessed remarkably similar kinetic behavior and carbohydrate specificities. All were inhibited by galactose, xylose, and inositol (very similar K_i values from plant to plant) and had very similar K_m values for the substrate, p-nitrophenyl -galactoside.

Gel filtration analysis of extracts from nine species suggests that legume -galactosidase activities may frequently reside in two molecular weight forms. However, all these species contained a large molecular weight enzyme activity with a size comparable to the -galactosidase-hemagglutinins.

Immunochemical studies reveal that the -galactosidases in these plants are immunologically related to an -galactosidase-hemagglutinin and, therefore, are related to one another.

These studies suggest that each of the legume species studied (and perhaps all members of this plant family) contain a homologue from a specific class of -galactosidase. Although the previously described -galactosidase-hemagglutinins appear to be members from this enzyme class, these proteins most frequently occur as forms devoid of hemagglutinin activity.