Immobilization of membrane enzymes into magnetizable, phospholipid bilayer-coated, inorganic colloids

Abstract

Nanometer-sized magnetic particles, which can be efficiently captured in a magnetic filter device during high-gradient magnetophoresis, were encased by a phospholipd bilayer made of the zwitterionic dimyristoylphosphatidylcholine. Evidence for the bilayer configuration of the lipid coat was mainly derived from equilibrium adsorption experiments. Lipid-depleted, beef-heart cytochrome c-oxidase, used as a model enzyme, was incorporated into these so-called magnetoliposomes by sonication. As a result, the enzyme demonstrates a 15-fold enhancement of its activity, which is comparable with the degree of reactivation measured in the presence of small unilamellar vesicles. The suitability of this type of catalytic biocolloids for biotechnological purposes is further demonstrated in a miniature pilot, fixed-bed bioreactor in which the enzyme-phospholipid-magnetite complex is first trapped by magnetic forces on the magnetic filter and subsequently overflowed with a solution of reduced cytochrome c. In this continuous mode of operation, the conversion efficiency remains almost constant on a time-scale of hours. Consequently, magnetoliposomes carrying membrane enzymes show up as promising entities to be used in magnetically controlled bioreactors.