Résumé
alpha-Galactosidase was isolated from germinating guar. The extract also contained small amounts of alpha-mannosidase and beta-mannosidase activities. The fractionation of the enzyme extract with ammonium sulphate (75% saturation) resulted in the appearance of all the three enzymes in a floating lipid complex. The inclusion of detergents such as Triton X-100 and sodium deoxycholate in the extraction medium failed to prevent the appearance of these enzymes in the floating lipid complex. However, by using acetone powder of the seedlings, alpha-galactosidase could be sedimented with ammonium sulphate. The presence of detergents in the extraction medium affected the molecular properties of the enzyme. Using a set of carefully selected conditions alpha-galactosidase was purified to apparent homogeneity. Analytical ultracentrifugation and gel filtration studies of the purified enzyme showed association-dissociation phenomenon as a function of pH and temperature. The effect of pH on the association-dissociation indicates the predominance of electrostatic interactions in the association of subunits.