Impact of the surface charge of magnetoproteoliposomes on the enzymatic oxidation of cytochrome c

Abstract

Upon immersing nanometer-sized Fe₃O₄ colloids in aqueous dispersions of phospholipid vesicles, a lipid bilayer is generated on the particle surface. The resulting “magnetoliposomes” can act as excellent hosts for membrane-bound enzymes, such as cytochrome c oxidase [De Cuyper and Joniau, Biotechnol. Appl. Biochem. 16, 201–210 (1992)].

In an attempt to tailor the catalytic properties of the immobilized enzyme, in the present study, we have explored the pivotal role played by the surface charge density of the magnetoliposome coat. In this respect, we have screened a series of bilayered phospholipid coatings consisting of anionic dimyristolyphosphatidylglycerol (DMPG), zwitterionic dimyristoylphosphatidylcholine (DMPC) or variable mixtures of the two. A cationic lipid coating, made of a heterogeneous mixture of DMPC and dioctadecyldimethyl-ammoniumbromide, was also tested. The profiles, representing the enzymatic activity which was measured spectrophotometrically at 550 nm and, if need be, corrected for scattered light due to clustering phenomena, showed that the highest degree of catalytic activity of lipidembedded enzyme was found when moderately charged, anionic magnetoliposomes (5 to 10% DMPG) were used. The results are interpreted in terms of a different affinity of the substrate for the various membrane types.