EFFECTS OF FUMONISIN B-1 AND (HYDROLYZED) FUMONISIN BACKBONE AP(1) ONMEMBRANES - A SPIN-LABEL STUDY

Electron spin resonance (ESR) spectroscopy and spin label techniques h ave been used to study the effects of fumonisin B-1 (FB1) and hydrolyz ed fumonisin backbone (AP(1)) on the structural and dynamic properties of phosphatidylcholine membranes at the molecular level. Multilamella r liposomes consisting of dimyristoylphosphatidylcholine (DMPC) and eg g yolk phosphatidylcholine (EYPC) were used. Six different nitroxide s pin labels were used to determine what effects FB1 may impart on the o rdering and mobility of lipids in membranes. The experimental results disclose the following: (1) In the fluid phase membrane, FB1 significa ntly increases the fluidities of n-doxylstearic acid (SA) spin labels (SL) attached to carbons 5 and 7, which disorders the alkyl chains and perturbs the surface region of the bilayer; by comparison, minimal ef fects were detected near the center of the bilayer. (2) In the gel pha se, FB1 and AP(1) imparts marked rigidifying effects on membrane fluid ity, which enlarges the change in ordering on the phase transition eve n further. (3) FB1 also restricts the mobility of the (rigid) cholesta ne spin label. (4) A reduction in mobility of the tempo-stearate spin label suggests that the tricarballylic acid (TCA) moieties of FB1 migh t mimic the structure of polar headgroups in phospholipids. The presen t results may provide additional mechanisms to elucidate the toxicolog ical activities of the fumonisins. (C) 1996 Academic Press, Inc.