Cercospora beticola toxins. IX. Relationship between structure of beticolins, inhibition of plasma membrane H+‐ATPase and partition in lipid membranes

Beticolins are yellow toxins produced by the fungus Cercospora beticola. The effect of one of them, beticolin‐1. has been investigated on corn root plasma membrane H+‐ATPase (EC 3.6.1.35) at different purification levels (plasma membrane fraction, partially, or highly purified enzyme). The results obtained demonstrated that (1) the purified proton pump was inhibited directly by low amounts of the toxin (I50= 1.62 ± 0.18 μM), (2) the biological effects of beticolin‐1 were similar to those of CBT (Cercospora beticola toxin). Furthermore, it was established that the efficiency of the different beticolins was clearly related to their ability to interact with the lipid bilayers, determined by fluorometric studies: the toxins that exhibited the lower I50 (50% inhibitory concentrations) values were the molecules that had the lowest partition coefficient to liposomes.