Transglycosidase operating by a ping-pong reaction mechanism. Involved in the synthesis of raffinose, a major soluble carbohydrate in seeds, roots and tubers. Specific for galactinol and p-nitrophenyl-alpha-D-galactoside as galactosyl donors. Able to utilize sucrose, lactose, 4-beta-galactobiose, N-acetyl-D-lactosamine, trehalose and lacto-N-biose as acceptors. May also act as a glycoside hydrolase. alpha-D-galactosyl-(1->3)-1D-myo-inositol + sucrose = myo-inositol + raffinose Inhibited by Ag(2)+, Hg(2+), Zn(2+), p-chloromercuribenzoate (pCMB) and 1-deoxygalactonojirimycin. Optimum pH is 7.0. Optimum temperature is 45 degrees Celsius. Belongs to the glycosyl hydrolases 36 family.