Dopachrome conversion activity in Aedes aegypti: significance during melanotic encapsulation of parasites and cuticular tanning.

Phenol oxidase (PO) and dopachrome conversion enzyme (DCE) were partially purified from Aedes aegypti larvae by ammonium sulfate fractionation. PO from A. aegypti functions in the hydroxylation of monophenols (e.g., tyrosine and tyramine) to their related o-diphenols, and the oxidation of o-diphenols (e.g., L-dopa, dopamine, N-acetyldopamine) to their respective o-quinones. Partially purified DCE showed high specificity toward dopachrome generated from dopa with the L-configuration. The combined effects of PO and DCE significantly accelerated melanization pathways when L-dopa was used as substrate. Significant DCE activity also was detected in hemolymph samples from adult, female A. aegypti, and undoubtedly plays a role in melanotic encapsulation reactions.