Properties of Amyloglucosidase in the Digestive Tract of Periplaneta americana L. (Blattodea: Blattidae)

Aim: Partial purification and characterization of amyloglucosidase from an insect were carried out to determine the physicochemical properties of the enzyme.

Study Design: It was designed to dissect digestive tracts from the American cockroach, Periplaneta americana, and to investigate the properties of the gut amyloglucosidase with a view to predicting possible industrial and pest control applications.

Place and Duration of Study: The study was carried out in the Insect Physiology Laboratory of the Department of Crop Production and Protection and Department of Biochemistry, Obafemi Awolowo University, Ile-Ife, Nigeria between June and October, 2013.

Methodology: Newly emerged cockroaches were dissected in ice-cold phosphate buffer and digestive tracts were collected to prepare the crude enzyme extract. Standard bioassays were constituted to purify and characterize amyloglucosidase.

Results: The purification had a 71.6% yield and a specific activity of 2.53 U/mg protein. On soluble starch, the enzyme exhibited optimum activity at pH 4.0 with a Michaelis constant (Km) of 1.67 mg/ml and a maximum velocity (Vmax) of 10mg/ml/min. Amyloglucosidase activity was enhanced by Mn2+ but it was slightly inhibited by Sn2+, Mg2+ and Ni2+, while Zn2+ caused a 50% inhibition. Optimum temperature for the partially purified enzyme was 40°C and it lost about 90% of its original activity when incubated beyond 20 min at 60°C.

Conclusion: Obtained results suggested that starch degradation using amyloglucosidase from P. americana could be done around pH 4 and at temperature around 40°C. This work appears to give the first report on physicochemical properties of amyloglucosidase in insects. Further studies would be needed to determine the possibility of using molecular techniques in inducing amyloglucosidase-Zn2+ complex in P. americana and to find a probable source of thermophilic amyloglucosidase which would be of importance in an industrial context.