Artificial flavolipid. Its synthesis, incorporation into liposomal membrane, electron transport, and successful control of transport rate

Abstract

The artificial flavolipid which has a flavin unit in the vicinity of the phosphatidylcholine moiety has been synthesized and found to be an effective electron transport catalyst across the bilayer membrane; it has also been successfully incorporated into lecithin liposome to give a stable product. The latter was shown to have, from dynamic light scattering and electron microscopic measurements, a single-walled, normal liposome structure of ca. 360 Å diameter and was as stable as the parent egg lecithin liposome. Clear biphasic kinetics were observed on reduction of the flavolipid in the bilayer membrane. The faster process was ascribed to reduction of the flavolipid in the outer half layer of the bilayer and the slower to the reduction of the flavolipid in the inner. The electron transport rate across the bilayer membrane from the external Na₂S₂O₄ to the internal K₃Fe(CN)₆ was much facilitated by the presence of the flavolipid in the membrane: detailed kinetic studies demonstrated that electrons were transported via a transient transmembrane channel consisting of two flavolipid molecules. The transport rate across the membrane was controlled by a thermally induced phase transition of the bilayer structure.