WOUND ACTIVATION OF PROTOXINS IN MARINE SPONGE APLYSINA-AEROPHOBA

The marine sponge Aplysina aerophoba accumulates brominated isoxazolin e alkaloids, which include aerophobin-2, aplysinamisin-1, and isofistu larin-3 as major constituents. Following disruption of compartmentaliz ation, the isoxazoline alkaloids are enzymatically converted to aeropl ysinin-1, which in rum gives rise to a dienone. The described bioconve rsions were demonstrated for the first time in vitro using an enzyme p reparation from A. aerophoba. Cell-free extracts of other Aplysina spe cies were capable of performing the same bioconversions, whereas enzym e extracts of sponges from other orders, which lack isoxazoline alkalo ids, were inactive with regard to the reactions analyzed. These findin gs suggest that the enzyme activities studied are linked to the accumu lation of suitable substrates and hence represent a specific biochemic al property of sponges from the genus Aplysina. Time-course experiment s with A. aerophoba, performed in situ, demonstrated that wound-induce d bioconversions of isoxazoline alkaloids proceeded rapidly. Within 40 sec after mechanical damage of a tube of A. aerophoba, both aerophobi n-2 and aplysinamisin-1 were completely converted to the dienone. The wound activation of protoxins results in a pronounced increase of the fish deterrent activity of A. aerophoba as shown in bioassays employin g the common Caribbean wrasse Thalassoma bifasciatum.