Catalytic and thermodynamic properties of an acidic α-amylase produced by the fungus Paecilomyces variotii ATHUM 8891

Abstract

An extracellular acid stable α-amylase from Paecilomyces variotii ATHUM 8891 (PV8891 α-amylase) was purified to homogeneity applying ammonium sulfate fractionation, ion exchange and gel filtration chromatography and exhibited a reduced molecular weight of 75 kDa. The purified enzyme was optimally active at pH 5.0 and 60 °C and stable in acidic pH (3.0-6.0). K _m, v _max and k _cat for starch hydrolysis were found 1.1 g L^-1, 58.5 μmole min^-1 (mg protein)^-1, and 73.1 s^-1, respectively. Amylase activity was marginally enhanced by Ca²⁺ and Fe²⁺ ions while Cu²⁺ ions strongly inhibited it. Thermodynamic parameters determined for starch hydrolysis (Ε _α, ΔH*, ΔG*, ΔS*, ${\Delta G}_{E-S}^{\ast }$ and ${\Delta G}_{E-T}^{\ast }$ ) suggests an effective capacity of PV8891 α-amylase towards starch hydrolysis. Thermal stability of PV8891 α-amylase was assessed at different temperatures (30-80 ^οC). Thermodynamic parameters ( $E_{\left(a\right)d}$ , ΔH*, ΔG*, ΔS*) as well as the integral activity of a continuous system for starch hydrolysis by the PV8891 α-amylase revealed satisfactory thermostability up to 60 °C. The acidic nature and its satisfactory performance at temperatures lower than the industrially used amylases may represent potential applications of PV8891 α-amylase in starch processing industry.

Keywords: Acidic α-amylase; Kinetic parameters; Paecilomyces variotii; Thermodynamic parameters.