Affinity chromatography of yeast alpha-glucosidase using ligand-mediated chromatography on immobilized phenylboronic acids.

The synthesis of 3-nitro-4-(6-aminohexylamido)phenylboronic acid is described. The properties of two novel forms of immobilized phenylboronate agarose adsorbents [m-aminophenylboronic acid-Matrex Gel and 3-nitro-4-(6-aminohexylamido)phenylboronic acid-Sepharose CL-6B] were investigated. Both gels bind and selectively retard the glycoprotein alpha-glucosidase from yeast. The retardation is affected by following parameters: (i) pH, (ii) presence of sugar, (iii) concentration of sugar and (iv) buffer species (especially triethanolamine). Five sugars were studied, namely sorbitol, fructose, ribose, glucose and maltose. The concentration of sugar required to produce significant retardation increased in the above order, whereas the ability of sugar to form a complex with boron decreases in the same order. These effects were observed with crude as well as pure enzyme. Since alpha-glucosidase is a glycoprotein, it is proposed that this protein is mainly bound to these immobilized phenylboronates via sugar (glyco) residues. Displacement of the enzyme from the column is effected by the sugar in the buffer (or in a preincubation mixture). However, the marked pH-dependence (this retardation effect could only be observed at pH 7.4) suggests that these results are not due solely to hydrophobic or ionic mechanisms and are more complex than simple sugar-phenylboronic acid interactions.