Formulation and Kinetics of the Glucansucrase Reactions

When an acceptor A is present, acceptor reactions can occur, diverting G away from incorporation into glucan. When the concentration of A is high with respect to that of S, reaction iii is inhibited and reactions v, vi, and xiii are favored to give acceptor products in reactions x, xv, and xvi. Some of these reactions (jcv, jcvi, and xvii) give free enzyme E that has to be glucosylated by reaction i before ANY products can be formed. In one instance (reaction iv), the acceptor forms a complex with free enzyme and this intermediate must be glucosylated by reaction ix before any products can be formed by reaction jcv. 

This reaction scheme does not take into account the negative allosteric effect of sucrose concentrations above 200 mM or the positive allosteric effect of low concentrations of glucan. 

Even though the reaction scheme is complex, attempts have been made to model the reaction and develop kinetic equations. Mooser et al.lu developed kinetic equations for a limited case based on the primer mechanism. Reh et a/.145 developed kinetic equations for the synthesis of dextran and for the maltose acceptor reaction based on the two-site insertion mechanism. Likewise, Boker et al,146 developed a kinetic equation for the formation of the fructose acceptor product, leucrose, based on the two-site insertion mechanism that included an acceptor site. An equation was derived for the overall reaction rate that was a function of the consumption of sucrose by dextran formation and acceptor-product formation. 

Shimamura, H. Tsumori, and H. Mukasa, Biochim. Biophys. Acta, 702 (1982) 72-80. 

Yakushiji, and M. Inoue, FEMS Microbiol. Lett., 16 (1983) 127-130. 

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