INHIBITION, TRANSGALACTOSYLATION AND MECHANISM OF ACTION OF SWEET ALMOND ALPHA-GALACTOSIDASE

The presence of essential catalytic groups in sweet almond α-galactosidase (α-d-galactoside galactohydrolase, EC 3.2.1.22) has been investigated with the use of metal ions and photo-oxidation. Competitive inhibition was shown to occur with both Hg2+ and Ag+. From the inhibition data it was postulated that carboxyl and histidine groups in the enzyme active site were responsible for binding the metal ions. The latter group was destroyed by photo-oxidation resulting in inactivation of the enzyme. The enzyme was found to catalyse hydrolytic, transgalactosylation and synthetic reactions on the same active site. All the reactions proceeded yielding products with complete retention of configuration. Two possible mechanisms of action have been suggested and discussed. © 1969.