Properties of the extracellular alkaline inulinase produced by haloalkaliphilic phototrophic bacteria Ectothiorodospirea mobilis

Abstract

The studies have revealed alkaline exoinulinase produced by haloalkaliphilic phototrophic bacteria Ectothiorhodospirea mobilis Al-2 for the first time. A new method for the isolation of a homogeneous exoinulinase from the culture broth was developed and the properties of this enzyme have been investigated. It was shown that specified exoinulinase in contrast to the studied exoinulinases produced by microorganisms exhibits catalytic activity at the wide range of pH (7.0–10) and a temperature (20–60 °C) with a maximum of the inulolitic activity at pH 9.0 and 50 °C. The studied exoinulinase possessing also invertase activity (I/S1.4) is a monomeric protein with molecular mass 57Kda, as well as Km and Vmax for inulin 3.8 mM/ml and 10 µmol/ml/min⁻¹, respectively. The studies of the influence of different metal ions on enzyme activity have shown that Mn⁺², Cu⁺², Co⁺², Mg⁺², NaCl 5–7% promote relatively higher catalytic activity while Zn⁺², Cu⁺² and Fe⁺² partially suppress the enzyme activity and Hg²⁺completely inactivates the enzyme.

The formation of only fructose and glucose at the enzymatic hydrolysis of inulin confirms that the studied exoinulinase belongs to the exo-type of enzymes. The obtained results supplement our fundamental knowledge in biochemistry-enzymology, as well as the biodiversity of microorganisms expressing exoinulinase. The studied exoinulinase exhibits activity at salinity of the medium and can potentially be used in the biotechnology of inulin bioconversion into bioproducts under alkaline conditions.