Genomic and cDNA sequence of prophenoloxidases from Drosophila melanogaster.

Abstract

Phenoloxidase (PO) is an important enzyme associated with the biochemistry of three physiologically important processes in insects. The first process, viz., cuticular sclerotization, ensures the protection of the soft bodied insects from their predators and preys as well as from desiccation by hardening the cuticle (Andersen et al.,1996; Sugumaran 1991; 1998). During sclerotization, PO generated quinones serve both as sclerotizing agents and as substrates for quinone isomerases that produce quinone methides (Sugumaran, 1998; Saul & Sugumaran 1988, 1989 a,b,1990, Ricketts & Sugumaran 1994). The reactions of quinones and quinone methides with cuticular structural components viz., chitin and proteins, lead to the hardening of cuticle (Andersen et al., 1996; Sugumaran 1991, 1998). In the second process, organisms establishing successful entry into the insect hemocel face among other host defense reactions, the dreaded action of PO, which causes deposition of melanin pigment around the intruder (Ashida & Brey 1995; Gillespie et al., 1997>; Nappi & Sugumaran 1993; Soderhall, et al., 1990; Sugumaran, 1996; Sugumaran & Kanost, 1993). While the intruder may still live in side the melanotic encapsule, its ability to multiply and damage the host is dramatically hindered by the melanotic capsule. Finally during wounding, loss of insect hemolymph is arrested by the rapid deposition melanin at the wounding site (Lai-Fook, 1966; Sugumaran, 1996). Apart from sealing the wound, PO action may also provide cytotoxic quinones that could harm the opportunistically invading microorganism (Nappi & Sugumaran 1993; >Sugumaran 1996).