A ferromagnetic modifier was prepared by reacting ferrous(Fe
2+)- and ferric(Fe
3+)-ions with polyethylene glycol having two carboxyl groups (MW:2000) at pH 8.0–8.5. Lipase from
Pseudomonas
fragi 22–39B was coupled with the modifier using water-soluble carbodiimide. The modified lipase, which was dispersed into buffered solutions in the size range of 30–70 nm, exerted the hydrolytic activity of 8.0 U/mg. In a magnetic field of 250 Oe, the ferromagnetic-modified lipase was readily recovered from the colloidal solution.