Characteristics of invertase from the alimentary canal of the pea aphid, Acyrthosiphon pisum (Harr.) (Homoptera, Aphididae)

Abstract

The optimum hydrogen-ion concentration for the action of invertase from the alimentary canal of the pea aphid, Acyrthosiphon pisum, was determined as pH 6·2 at 37°C. The enzyme activity constantly increased during the first 5 hr of incubation, the activity and incubation time curve showing a straight-line relationship. The optimum temperature for the action of the enzyme was 35°C. A sucrose concentration of 45 mg/ml of the reaction mixture was most favourable for the enzyme activity at pH 6·2 and 37°C. Like the most common animal invertase, the enzyme hydrolysed sucrose, trehalose, melizitose, turanose, and maltose but did not hydrolyse melibiose or raffinose; it is therefore an α-glucosidase. The enzyme did not usually catalyse transglucosidation, although in one test traces of oligosaccharides were detected. A very weak invertase activity was also occasionally detected in pea aphid honeydew.