It is shown that D-enzyme (Nature, 1953, 172, 158) is different from phosphorylase, R-enzyme, and the amylases. It has not yet been possible to separate D-enzyme from Q-enzyme but it is demonstrated that the branching and the disproportionating activity are due to independent enzymes. Evidence is presented which shows that D-enzyme is a transglycosylase, transferring two or more glucose units from a maltodextrin substrate to a suitable acceptor and that, in the transfer, only α-1 : 4-glucosidic links are synthesised. The natural substrates for D-enzyme appear to be the maltodextrins, from maltotriose upwards; neither glucose nor, in all probability, maltose functions as donor substrate. The enzyme is not so selective with respect to the " accepting " molecule. The anomalous position of maltose in this system is discussed.
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