Substrate specificity and catalytic properties of glucoamylase from Leohumicola incrustata

Abstract

Glucoamylase from fungi has proved to be a very useful enzyme for industrial processes by improving yields of food and starch products. This study determined specific and catalytic properties of purified glucoamylase obtained from a fungus, Leohumicola incrustata (MF374380). The enzyme was produced using submerged fermentation method and crude enzyme obtained was centrifuged and purified. Avicel, beechwood (BW) xylan, carboxymethylcellulose (CMC), colloidal chitin, and soluble starch as well as glycogen, amylose, amylopectin, maize starch (raw), and blocked p-nitrophenyl-α-D-maltoheptaoside (BpNPG7) were used for substrate specificity assay. Michaelis-Menten plot was also used to determine catalytic properties of the enzyme. Findings revealed that the purified glucoamylase (37.6 U/mg protein) was specific for only starch while the enzyme could not hydrolyze Avicel, BW xylan, CMC, colloidal chitin and BPNPG7. Michaelis-Menten plots results showed a K_m value of 0.70 mg/mL on glycogen, followed by amylopectin, amylose, and raw maize starch, with K_m values of 0.76, 1.05, and 1.77 mg/mL, respectively. The K_cat values for raw maize starch, amylopectin, glycogen, and amylose were 73, 66, 57, and 32 s^-1, respectively. Therefore, the study revealed that enzyme from L. incrustata exhibited strong substrate affinity and catalytic properties. The study underpins the need to include this organism when prospecting for future industrial glucoamylase production.