CERCOSPORA-BETICOLA TOXINS .7. FLUOROMETRIC STUDY OF THEIR INTERACTIONS WITH BIOLOGICAL-MEMBRANES

The interactions of two beticolins, Cercospora beticola toxins, and of their magnesium complexes with liposomes or plasma membrane were stud ied. The fluorometric pH titration curves of beticolins in liposomes a nd in plasma membranes reveal the presence of the dissociated form of beticolins. The concentration of the magnesium complex in these membra nes increases at high pH. The partition coefficient of beticolin-1 on liposomes is 3-fold higher than that of beticolin-2 and the fluorescen ce of both compounds on liposomes is similar. The addition of magnesiu m to liposomes causes a 40-fold and 20-fold increase in the partition coefficient of beticolin-1 and -2, respectively, as a result of the in teractions between membrane, magnesium and beticolins. Beticolins reac t to a Delta pH across the liposome membrane but the formation of the magnesium complex completely abolishes this effect.