초록
<P/><P>The α-glucosidase encoded by the <I>aglA</I> gene of <I>Aspergillus niger</I> is a secreted enzyme belonging to family 31 of glycoside hydrolases. This enzyme has a retaining mechanism of action and displays transglycosylating activity that makes it amenable to be used for the synthesis of isomaltooligosaccharides (IMOs). We have expressed the <I>aglA</I> gene in <I>Saccharomyces cerevisiae</I> under control of a galactose-inducible promoter. Recombinant yeast cells expressing the <I>aglA</I> gene produced extracellular α-glucosidase activity about half of which appeared cell bound whereas the other half was released into the culture medium. With maltose as the substrate, panose is the main transglycosylation product after 8 h of incubation, whereas isomaltose is predominant after 24 h. Isomaltose also becomes predominant at shorter times if a mixture of maltose and glucose is used instead of maltose. To facilitate IMO production, we have designed a procedure by which yeast cells can be used directly as the catalytic agent. For this purpose, we expressed in <I>S. cerevisiae</I> gene constructs in which the <I>aglA</I> gene is fused to glycosylphosphatidylinositol anchor sequences, from the yeast <I>SED1</I> gene, that determine the covalent binding of the hybrid protein to the cell membrane. The resulting hybrid enzymes were stably attached to the cell surface. The cells from cultures of recombinant yeast strains expressing <I>aglA-SED1</I> constructions can be used to produce IMOs in successive batches.</P>