Effect of chemical modification using glyoxylic acid on the stability of α-amylase from <i>Aspergillus fumigatus</i>

Abstract In this present work, α-amylase isolated from Aspergillus fumigatus was successfully modified using glyoxylic acid. The enzyme was isolated through centrifugation and purified using (NH 4 ) 2 SO 4 salt deposition and dialysis. The purified α-amylase exhibited a purity level 17.79 times higher than that of the crude extract. The study also found that the optimum pH for α-amylase was 5.0, while for the α-amylase/glyoxylic acid an optimum pH of 5.5 was observed. Both the native and modified α-amylase showed an optimum temperature of 55 °C. The native α-amylase has the K M values of 11.55 mg mL −1 substrate and V max of 10.76 mol mL −1 min −1 . In contrast, the α-amylase/glyoxylic acid complex has the K M values ranging from 14.67 to 16.73 mg mL −1 substrate and V max ranging from 7.07 to 9.32 mol mL −1 min −1 . The residual activity of the native enzyme after incubation for 100 min at 60 °C was 9.34 %, while the modified enzyme exhibited residual activities ranging from 28 to 59 %. The Δ G i for the native α-amylase was 104.333 kJ mol −1 , while for the modified enzyme, the values in the range of 105.825–106.314 kJ mol −1 were found. Another important finding is significantly higher stability of the modified enzyme compared to the native enzyme, α-amylase, as evidenced by an increase in half-life ( t ½ ) ranging from 1.71 to 2.05 times.