The control of prophenoloxidase activation in larval haemolymph of Calliphora

Abstract

Spontaneous activation of prophenoloxidase on exposure to air occurs most rapidly in haemolymph from early (day 4) and late (day 11) third instar larvae of Calliphora. On and after day 6 of development, haemolymph contains an inhibitor of proenzyme activation which can be removed by ultrafiltration. An activator of prophenoloxidase is present in the cuticle of the body wall throughout third instar. The lowest level of this activator is found at day 4; later it is detectable in cuticle from tracheae and salivary ducts. Secretory cells of the salivary gland liberate in vitro a potent inhibitor of prophenoloxidase activation. Whole salivary glands including attached ducts may enhance or retard phenoloxidase activity in diluted haemolymph, depending on the age of the larvae which provide glands and plasma. The inhibitor concentration in the haemolymph rises contemporaneously with increased inhibitory potential in the salivary gland. Inhibitor from salivary glands shares certain physical properties with that from haemolymph. Salivary ducts and whole salivary glands of species of Drosophila affect melanization of Calliphora haemolymph in a pattern which suggests that the activator and inhibitor components in these genera have similar tissue distributions, and lack species-specificity.