Which Phenoloxidase Catalyzes Insect Cuticle Tanning, Laccase or Tyrosinase?
Tanning or sclerotization is a vital process during insect development in which N-acylcatecholamines are oxidatively conjugated to cross-link proteins and stabilize the exoskeleton. The phenoloxidases laccase (Lac) and tyrosinase (Tyr) have been proposed to catalyze tanning, but evidence reported to date identifying the actual tanning enzyme has been inconclusive. To establish the involvement of either or both of these phenoloxidases in cuticle tanning, we performed RNA interference (RNAi) experiments using the red flour beetle, Tribolium castaneum. RNAi can be used to suppress specific messenger RNAs and generate loss-of-function phenotypes. We have knocked down phenoloxidase mRNAs and examined the phenotypes for effects on adult cuticle tanning. The results reported here demonstrate that laccase and not tyrosinase plays the major role in cuticle tanning.
