Kinetik und Mechanismus der enzymatischen Dextransynthese und Wirkung der Akzeptoren auf diese Reaktion

Abstract

According to the proposed mechanism, the enzymic formation of dextran from sucrose consists of two reaction steps: the propagation reaction forming polymer molecules by an insertion type growth, and the acceptor reaction leading to the termination of the polymer chains. This mechanism is of a more general applicability; it explains hydrolysis, transfer and poly reactions. A complete kinetic analysis is given for the dextran formation and values for the reaction constants Vm, Km and Ka (the Michaelis constant of the acceptor reaction) have been evaluated. Very good agreement between the rate data calculated from the mechanism and the experimental data has been obtained. From experiments with a series of radioactively labelled acceptors it was established that the acceptor reaction, in fact, proceeds as proposed by the mechanism. Further, it was found that strong acceptors, leading to the formation of low molecular weight dextrans, do not inhibit the reaction rate, and that weak acceptors, which inhibit the reaction rate, have only a small effect on the molecular weights. This correlation has also been demonstrated in terms of the proposed reaction mechanism.