CERCOSPORA-BETICOLA TOXINS .9. 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 beticol a. The effect of one of them, beticolin-1, has been investigated on co rn root plasma membrane H+-ATPase (EC 3.6.1.35) at different purificat ion levels (plasma membrane fraction, partially, or highly purified en zyme). The results obtained demonstrated that (1) the purified proton pump was inhibited directly by low amounts of the toxin (I-50=1.62+/-0 .18 mu M), (2) the biological effects of beticolin-1 were similar to t hose of CBT (Cercospora beticola toxin). Furthermore, it was establish ed that the efficiency of the different beticolins was clearly related to their ability to interact with the lipid bilayers, determined by f luorometric studies: the toxins that exhibited the lower I-50 (50% inh ibitory concentrations) values were the molecules that had the lowest partition coefficient to liposomes.