Purification and biochemical characterisation of glucoamylase from a newly isolated Aspergillus niger: Relation to starch processing

Herein, we investigate a glucoamylase from newly isolated Aspergillus niger. The enzyme was purified, using fractionation, followed by anion-exchange chromatography and then characterised. The molecular mass of the enzyme was estimated to be ∼62,000 Da, using SDS–PAGE and 57151 Da, based on mass spectrometry results. The pI of the protein, and optimum pH/temperature of enzyme activity were 4.4, 5 and 70 °C, respectively and the kinetic parameters (Km, Vmax and kcat) were determined to be 0.33 (mg ml−1), 0.095 (U μg−1 min−1) and 158.3 (s−1) for soluble starch, respectively. The glucoamylase nature of the enzyme was also confirmed using TLC and a specific substrate. Metal ions Fe3+, Al3+ and Hg2+ had the highest inhibitory effect, while Ag2+, Ca2+, Zn2+, Mg2+ and Cd2+ and EDTA showed no significant effect on the enzyme activity. In addition, thermal stability of the enzyme increased in the presence of starch and calcium ion. Based on the results, the purified glucoamylase appeared to be a newly isolated enzyme.