Abstract
Potato D-enzyme is a transglycosylase that disproportionates maltotriose and higher maltodextrins by the transfer of maltodextrinyl radicals between maltodextrins. with the rupture and re-formation of α-(1 → 4)-
d-glucosidic bonds. Only maltodextrins or similarly structured polymers are group-donating substrates.
d-Glucose and a variety of other sugars can act as acceptors. Earlier workers had noted that D-enzyme appears to operate on maltodextrins under constraint. Maltose is not a donor substrate. Only one bond in maltotriose, that at the reducing end, is acted on. In the higher dextrins, there are two “forbidden” linkages. The nonreducing-end bond, and that penultimate to the reducing end, cannot be split.
The present paper tests and fully supports the hypothesis of forbidden linkages and their locations in the donating molecule. The tests have involved quantitative examination of the way in which (
a) maltodextrins and
d-glucose-
14
C interact in the presence of D-enzyme, and (
b) maltotriose-
14
C is disproportionated into
d-glucose and other maltodextrins. It is noted that maltosyl groups are transferred more rapidly than any larger group, and that the rate of transfer of the maltosyl group to
d-glucose is equal in malto-triose, -pentaose, and -hexaose. (A maltosyl group cannot be transferred from the tetraose.)
