Theoretical and experimental study on the competition of NANA-aldolase and cytidine-5'-monophosphosialate-synthase for their common substrate N-acetylneuraminic acid.

The competition of NANA-Aldolase and Cytidine-5'-monophosphosialate-Synthase for their common substrate NANA has been studied, with, (i) the two enzymes in solution, (ii) NANA-Aldolase in solution and Cytidine-5'-monophosphosialate-Synthase immobilized in an artificial membrane (diffusion coefficient: 1.2 X 10(-3) cm2 h-1). The relation of the reaction rates for both enzyme was found 1:1 in case (i) and 2:1 in case (ii), in favor of NANA-Aldolase. These results are in agreement with the results obtained by computer simulation, where the Michaelian assumption and the diffusion effects had been considered. It was also calculated that the regulation of this branch point for the metabolic pathway of NANA is dependent on the input of NANA produced by the previous steps of the pathway and not on the concentration of CTP (second substrate of Cytidine-5'-monophosphosialate-Synthase) or the parameters controlling the diffusion of NANA. Computer simulations were performed by numerical analysis.