Evidence for phenoloxidase activity inHolothuria tubulosa (Echinodermata) brown bodies and cells

encapsulating structures occurred inHolothuria tubulosa. Histologically, they were formed by nodules entrapping foreign material. By an internodular mass, two or more nodules were assembled in an encapsulating body that was brown-pigmented. This pigment could be melanin, since an enzyme (i.e., phenoloxidase) responsible for its synthesis was proven. The enzyme exerted oxidase activity against dopa, dopamine and norepinephrine but not against tyrosine. The components of the sea-cucumber phenoloxidase-activating system were present in the circulating cells, which could therefore be responsible for melanin deposition during processes of foreign-body encapsulation.