EVIDENCE OF CYCLOIRIDALS AS MEMBRANE CONSTITUENTS - EFFECTS ON FLUIDITY PATTERNS COMPARED TO THOSE OF CHOLESTEROL

Two triterpenoids, iripallidal and iriflorental, known irone precursor s, were shown to be solubilized by phosphatidylcholine (PC). Elution o f liposomes (containing PC + iridals) on a Sephadex column showed that iridals and PC were always associated in the same fractions with comp arable PC/iridal molecular ratios. Moreover, the physical parameters o f dimyristoyl-PC membranes, measured by electron spin resonance were s pecifically modified by the presence of cycloiridals, indicating that they are integrated within liposomal membranes. These effects on fluid ity and phase-transition patterns were compared with those of choleste rol. The secondary plant products, iridals, seem to have a structural role within cells comparable to that of sterols. Possible ecophysiolog ical implications of iridals are discussed.