Conclusion
The immobilised particles provide a number of advantages. The individual spherical particles had a diameter of between 0.5–10 μm, but tended to form aggregates with an average particle volume distribution of 100 μm. The size could be controlled through addition of surfactant and variations in protein concentration. The particles were robust enough to be recovered by centrifugation and filtration, and to be recycled for further reactions. They present lipase enzymes with the active sites selectively orientated towards the exterior of the particle. Co-immobilisation with other enzymes, or other proteins such as albumin, was also demonstrated. Moreover, higher activity for small ester molecules could be achieved by the immobilised enzyme particles than for free enzyme, presumably because the lipase conformation required for catalysis had been locked in place during immobilisation. The immobilised enzymes also demonstrated superior activity in organic solvent compared to the original free enzyme. This type of self-immobilised enzyme particle has been named spherezymes.