Mechanism of carbohydrase action. XII. l-Sorbose as an acceptor substrate in transfer reactions catalyzed by potato D-enzyme

D-Enzyme, a transglycosylase from potato, has been found to transfer maltodextrin residues from starch to l-sorbose or methyl α-l-sorboside, as well as to d-glucose. Oligosaccharides terminated in l-sorbose or methyl α-l-sorboside are thereby formed. These have been isolated and found to contain α-maltosyl, α-maltotriosyl groups, etc., linked to C-3 of the sorbose or sorboside. The inability of D-enzyme to distinguish between l-sorbose and d-glucose as substrates results from the structural similarity between the two sugars, in particular the equivalence of the C-3 hydroxyl of sorbose, the site of reaction, with the C-4 hydroxyl of glucose. α-Amylase, β-amylase, and starch phosphorylase are likewise unable to differentiate between the two monosaccharides since they attack the sorbose- and sorboside-terminated oligosaccharides in the same way as the corresponding glucose-terminated polymers (maltodextrins).