Enhancement by gonyautoxin V of the iron(III) reducing or binding activity produced by the dinoflagellate, Alexandrium excavatum

Reduction or binding of Fe(III) by agent(s) produced by a highly toxigenic strain of Alexandrium excavatum was detected at approximately the same levels in culture filtrates of this dinoflagellate grown either axenically or non-axenically. Nanomolar concentrations of pure Paralytic Shellfish Poisons (PSP) produced by this phytoplankton, the carbamate toxins saxitoxin, 2/3 gonyautoxin or the N-sulfamoyl carbamate toxins C1/C2, added to a Schwyn and Neilands (1987) assay mixture did not stimulate Fe(III) reduction or binding. In contrast, additions of the N-sulfamoyl carbamate toxin, gonyautoxin V (GTXV also known as B1) alone resulted in a several-fold increase in this activity. The level of activity per cell was considerably higher for those cultures grown in media deficient in iron than in those whose growth was restricted by decreases of either N or P.