Use of immobilised glucoamylase G2 for separation of enantiomers

The aim of this study was to compare the isolated glucoamylase G2 domain as chiral selector with previously presented data obtained using immobilised native glucoamylase as chiral stationary phase. The glucoamylase G2 was isolated from a commercial preparation of Aspergillus niger glucoamylase and immobilised onto silica particles. Enantioselectivity was tested for several amino alcohols including the beta -receptor blocking agents metoprolol and alprenolol. Separation factors greater than 2 were observed. Mobile phase pH was varied to optimise the enantioselective recognition and several different uncharged additives were included to examine their effect on retention. For some of the tested solutes increased retention times were observed when increasing the content of uncharged modifier. Increased mobile phase concentration of several of the tested organic modifiers resulted in increased separation factors. The effect of column temperature was studied. Retention and enantioselectivity increased at higher temperatures. Addition to the mobile phase of acarbose, an inhibitor that binds to the catalytic site of G2 with picomolar affinity, resulted in total loss of enantioselectivity. Comparison of the present results with those obtained previously with the glucoamylase G1 form also containing a starch binding domain, shows that the catalytic domain is essential for chiral recognition of amino alcohols.