Mathematical model for aldol addition catalyzed by two d-fructose-6-phosphate aldolases variants overexpressed in E. coli

•Kinetic model for aldol addition catalyzed by two d-fructose-6-phosphate aldolase variants.•The same type of kinetic model could be applied for both enzymes.•Operational stability of enzymes was assessed in the batch and ultrafiltration membrane reactor. Two d-fructose-6-phosphate aldolase variants namely, single variant FSA A129S and double variant FSA A129S/A165G, were used as catalysts in the aldol addition of dihydroxyacetone (DHA) to N-Cbz-3-aminopropanal. Mathematical model for reaction catalyzed by both enzymes, consisting of kinetic and mass balance equations, was developed. Kinetic parameters were estimated from the experimental data gathered by using the initial reaction rate method. The model was validated in the batch and continuously operated ultrafiltration membrane reactor (UFMR). The same type of kinetic model could be applied for both enzymes. The operational stability of the aldolases was assessed by measuring enzyme activity during the experiments. FSA A129S/A165G had better operational stability in the batch reactor (half-life time 26.7h) in comparison to FSA A129S (half-life time 5.78h). Both variants were unstable in the continuously operated UFMR in which half-life times were 1.99 and 3.64h for FSA A129S and FSA A129S/A165G, respectively.