Effect of glycation on stability and kinetic parameters of thermostable glucoamylase from Aspergillus niger

The effect of glycation on properties of thermostable glucoamylase was studied by incubating purified glucoamylase with maltodextrin at 60°C. Glycation occurred during the incubation and was assessed by 5-(hydroxymethyl)-2-furfuraldehyde (HMF) released from acid hydrolysis of the glycated protein. Stability and kinetic parameters of the glycated glucoamylase and the intact enzyme were compared. The glycated enzyme was more resistant to the heat but glycation did not strongly affect pH stability and pI value significantly. In the presence of maltose as substrate, the K_m value of the glucoamylase glycated by maltodextrin was lower than that of the intact enzyme. This indicated a greater affinity of the glycated enzyme for maltose. In the presence of maltodextrin as substrate, glycation led to increases in the rate of hydrolytic reaction. Moreover, glycation resulted in a higher efficiency of glucoamylase to convert the substrate into glucose. This might be due to a greater conformational flexibility of the glycated glucoamylase.