Interaction with phospholipids as a possible mode of action of 3-phenylindole on Aspergillus niger

Low concentrations of 3-PI(3-phenylindole) inhibit several uptake and biosynthetic processes in liquid cultures of Aspergillus niger. The incorporation of ³²P_i into phospholipids, [¹⁴C]uridine into nucleic acids, and [¹⁴C]phenylalanine into proteins was inhibited and the uptake of all three precursors was reduced. Studies on an in vitro interaction between 3-phenylindole and phospholipids showed, that at about equimolar concentrations 3-phenylindole prevents phospholipids from swelling in water. At the same ratio a decrease of the absorption intensity of the NH-band of 3-phenylindole was observed in ir spectra. Moreover, the maxima of the uv spectrum of 3-phenylindole shifted after addition of a sonicated phospholipid suspension. It is suggested that binding to phospholipids is the first effect of 3-phenylindole. Apparently this affects, consequently, several membrane-bound reactions, i.e., transport and biosynthetic processes.