Studies of the haemolymph and cuticular phenoloxidase in Spodoptera littoralis larvae

Abstract

Active phenoloxidase was isolated from the larval haemolymph and cuticle. The activity of the haemolymph enzyme was very low, reaching only about 10 per cent of that of the cuticle. Proteolytic enzymes, acetone, and alcohols inhibited cuticle and haemolymph phenoloxidase to various extents. Potassium cyanide and sodium thiosulphate suppressed strongly the cuticle phenoloxidase; sodium azide and sodium chloride affected the enzyme activity to a much lesser degree. Chelating agents, such as sodium diethyldithiocarbamate, 2,3-dimercapto-propanol, d-penicillamine, and 8-hydroxyquinoline, inhibited strongly the phenoloxidase activity. Sodium diethyldithiocarbamate was the most effective compound, suppressing the enzyme activity at a concentration of 10 −6−10 −8 M. Its activity seems to result from tying up the active center(s) of the enzyme, and then blocking the substrate reaction.