Effect of metal ions on levan synthesis efficiency and its parameters by levansucrase from Bacillus subtilis

Levan is a fructan whose backbone is composed of β-(2-6) linkages. It is synthetized by the enzyme levansucrase (EC 2.4.1.10). The effect of Fe³⁺, K⁺, Mg²⁺, Mn²⁺, and Zn²⁺ in the range of 0-1 mM on parameters of levan was tested using design of response surface experiment. The bimodal distribution of levan was observed, however, the concentration of high molecular mass fraction (weight average molar mass, M_w = 1.9 · 10⁷ ± 3.4 · 10⁴ g/mol and intrinsic viscosity, [η] = 0.206 ± 0.016 dL/g,) was not >4% of the total yield of levan. The metal ions in the reaction medium had an effect on parameters of low molecular mass levan and the efficiency of synthesis. Molar mass distribution of abundant, low molecular mass fraction was in the range of 4.33 · 10⁴ g/mol to 9.77 · 10⁴ g/mol; [η] was 0.040-0.075 dL/g while the efficiency of transfructosylation was within the range of 61.4to 69.1%. It was observed that the molar mass of levan depends on Fe³⁺ concentration while intrinsic viscosity is affected by the concentration of Mn²⁺ in the reaction medium. The GPC (with triple detection) data was analyzed using response surface methodology (RSM), k-means and principal component analysis (PCA).