Specificity of sweet-almond α-galactosidase

Abstract

The specificity of purified sweet-almond [alpha]-galactosidase has been investigated with 17 substrates. Some of them exhibited inhibition at high substrate concentrations but others did not. Both substrate types were bound and hydrolyzed at the same site on the enzyme, The enzyme is specific for [alpha]-D-galactosides and [beta]-L-arabinosides. It did not hy-drolyze [beta]-D-galactosides or [alpha]-D-glucosides. Among galactosides the order of decreasing rates of enzymic hydrolysis was aryl [alpha]-galactos ides; sugars; alkyl [alpha]-galactosides. All substituents in the aryl moiety of aryl [alpha]-galactosides enhanced Vmax,. the electron-releasing ([long dash]) groups being more effective than the electron-withdrawing (+ ) groups. The substituent groups did not alter Km appreciably. Implications of these results are discussed from a mechanistic viewpoint.