Ultrastructural localization and antibacterial activity of phenoloxidase in amphioxus Branchiostoma belcheri tsingtauense

Phenoloxidase (PO) has been shown to be present in both invertebrates and v ertebrates, yet little is known about the PO in Branchiostoma belcheri tsin gtauense. The present study demonstrated that the PO activity existed histo chemically the epithelial cells of the gill bar and intestine of adult anim al, producing brown to black melanin deposits. Ultrastructural examination revealed that PO reaction products were localized in the cytoplasmic granul es of the epidermal cells, the epithelial cells of gill bar and intestine a nd most of them were electron-dense and homogenous. Frequently, the PO reac tion products were also observed in the secondary lysosomes. The mucus from the body surface had little antibacterial activity against E scherichia coli, but it enhanced the antibacterial activity of L-dopa and t he enhancement was suppressed by PTU, a PO specific inhibitor. This indicat es that the active material inhibiting the E. coli growth in the mucus is P O.