having 1.5% (w/v) total concentration from both types
of polymers. Spheres were prepared with 1:2, l:l, 3:2
and 2:1 final component ratios of X:A. Polymer ratio
versus maximum urease activity is plotted in Figure 1.
The glutaraldehyde-treated XA spheres (GAXA)
showed about 30% lower maximum activity when
compared with untreated ones (XA), but in both cases
the spheres gave optimum activity at 1:l polymer ratio.
Another observation was that GAXA spheres showed a
limited decrease in enzymatic activity of about l5-
16% between the 1:l and 2:l ranges. The situation
differed for the XA-type spheres with 3940%
decrease of enzyme activity, which indicated that a 2:1
(X:A) ratio was not suitable for trapping all the enzyme
molecules, and enzyme leakage occurred. We can say
that GA treatment causes a slight decrease in the
enzymatic activity but influences the stability of XA
spheres in varying component ratios by forming amide
bonds with the amine groups of the enzyme molecules
and gelatin’ (Figure I). The decrease in activity may be
attributed to the binding of active groups or intramolecular
cross-linking of enzyme molecules by GA,
which reduces the affinity of the substrate for the
active site of the enzyme. The high cross-linking ratio
will also lead to some mass transfer resistances
inherent in the morphology of the support used. This
situation may cause product accumulation inside the
microenvironment, leading to low substrate-product
conversion rate, and finally detection of lower
enzymatic activities.
Figure 2 shows the results obtained from the studies
of polymer ratio effect on water absorption capacity.
From the figure it is evident that water uptake of the