area of about 400 m^2 g–1bearing ethylenediamine groups on their surface (Deloxan
DAP III; Table 2) suitable for operating in aqueous as well as in organic media. The
standard immobilization procedure is enzyme fixation via glutaraldehyde, or by a
carbodiimide. We chose the glutaraldehyde method, and also immobilization by
azo coupling. For the latter, the ethylenediamine residues of the polysiloxane sup-
port were reacted withp-nitrobenzoylchloride, forming a peptide bond. After the
reduction of the –NO 2 – group to an –NH 2 – group, followed by diazotation, the
PLA 2 was bound to the Deloxan surface by a strong azo linkage. Furthermore,
13.4 Immobilization of phospholipases 277
Figure 7. (A) The activity of PLA 2 immobilized to Deloxan carriers (Degussa) by adsorption (HAP)
and by covalent binding (GDA, Diaz) as a function of the substrate concentration. The reaction medium
contained 20 % (v/v) ethanol. (B) If ethanol in the reaction mixture is exchanged for the same amount of
ethyl acetate, the activity increases by more than a factor of 4.
(A)
(B)