Another important parameter is the polarity of the reaction mixture, which can be
adjusted by the addition of water-soluble organic solvents. It has been shown that the
presence of ethanol stimulates the activity towards the attack of PC by PLA 2 (Grun-
wald et al., 1995). A preincubation of PLA 2 in organic solvents leads to a change in
theKmvalue, and the activation energy of PLA 2 , and in the case of preincubation in
1-butanol, the activity of this enzyme is markedly increased (Remus and Grunwald,
1995).
13.3 Immobilization of biocatalysts
Although immobilized biocatalysts are defined as enzymatically active materials
which are transformed artificially into a catalytically active and insoluble mode,
they have their counterparts in living organisms because many enzymes are asso-
ciated with cellular material.In vivo, the kinetics of such enzymes are influenced
by parameters such as the composition of the microenvironment where they act,
by conformational changes due to binding, or by mass transfer. Hence they may
play an important role in the complex control mechanisms within living cells, simi-
lar to that of allosteric enzymes. Accordingly, the behavior of enzymes that are im-
mobilized by fixation to the surface of a carrier, or by entrapment within a polymer
matrix, depends on the reaction conditions and the way in which immobilization is
carried out. Indeed, by using a specific choice of carrier material, the apparent prop-
erties of the enzymes can be altered.
266 13 Preparation and Application of Immobilized Phospholipases
Figure 1. A scheme for the continuous production of polar head group-modified phospholipids (1),
their purification by PA-removal (2), and hydrolysis to the corresponding organic phosphate (3), as pro-
posed by Servi (1999). The three enzymes PLD, alkaline phosphatase, and PLC are immobilized in hol-
low-fiber hydrophobic membrane reactors.