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Binding of Urease to Anodized Sheet Aluminum.

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Binding of Urease to Anodized Sheet Aluminum
By Peter Grunwald, Walter Gunsser, and Siegfried Scheed']
The fixation of proteins to water-insoluble materials has
become an important field of study in chemistry and related
disciplines"? Preference is often given to inorganic carriers
because they cannot be degraded by bacteria. The binding
of an enzyme to the carrier may be covalent or adsorptive
and usually entails a loss of activity. Criteria for the quality
of such a preparation include not only the residual activity
but, above all, the potential for repeated use and the thermal
stability.
In our studies on the adsorption of proteins on inert metal
oxides we found in the case of the enzyme urease that anodized
sheet aluminum is very suitable for this application.
Figure 1 shows the dependence of enzyme activity on the
conditions of anodization. While the reaction rate is still relatively low under the conditions of the well known G-S process
(hatched area),the activity of the adsorbate increases by almost
two powers of ten on surpassing a certain sulfuric acid concentration (current density). Scanning electron micrographs (Fig.
2) show the surface of an A1 sheet before and after loading
0
z
.
w,
10
20
H,SO,[wt.
'
'
'
-T
,
-
30
%I
with urease. The structure of the aluminum hydroxide surface
reveals the texture of the sheet aluminum used.
The thermal stability of urease fixed by adsorption to these
anodization layers compared with that of the free enzyme
in solution, whose optimum temperature is about 65"C, is
remarkable (see Fig. 3). Specific features of the temperature
dependence of urease are apparently retained in the adsorbate,
such as the anomalous course of urease-catalyzed hydrolysis
of urea described by Tulsky~2a]
as well as different activation
energies within different temperature ranges C50.8 kJ mol(5-20°C), 24 kJ mol-' (2CL4loC), 45.1 kJ mol-' (4196"C)I. The activation energies for hydrolysis of urea in the
presence of dissolved urease are 49 kJ mol (0-22 0C)[31and
36.5 kJmol-' (20-40°C)[zbl; we were able to confirm both
values for the enzyme we used for absorption as 49 kJ mol-I
(0-21 "C) and 36.5 kJ mol- (20.5-50°C). Relative to the
free enzyme, the adsorbate has a significantly lower activation
energy in the middle temperature range.
50
["C]
10
I
40
Fig. 1. Activity of anodized sheet aluminum as a function of the sulfuric
acid concentration; the activities were determined by conductometry.
Fig. 3. Temperature dependence of the hydrolysis of urea for dissolved urease
and urease adsorbed on anodized aluminum -o-o-o--.
-4-A-4-
The temperature dependence of urea hydrolysis was determined over the entire temperature range of 2 to 98°C (30
measurements) on the same preparation, thus adequately
demonstrating the possibility of repeated use of this carrierbound enzyme. If the supply of urease is not too high the
adsorbed enzyme exhibits greater activity than that in the
free state. Comparison with conventional inorganic carrier
materials[41shows that anodized sheet aluminum well satisfies
the criteria initially mentioned.
Received: July 22, 1977 [Z 807 IE]
German version: Angew. Chem. 89. 761 (1977)
a1
bl
Fig. 2. Scanning electron micrograph (magnification 2000 X) of an anodized
layer a) before and b) after charging with urease from the region beyond
the optimum activity (arrow in Fig. 1).
[*] Dr. P. Grunwald [ '1, Prof. Dr. W Gunsser, cand. HL S. Scheer
['I
lnstitut fur Physikalische Chemie der Universitat
Laufgraben 24, D-2000 Hamburg 13
To whom correspondence should be addressed
714
CAS Registry numbers:
Urease, 9002-13-5; Al, 7429-90-5
[l] H. D . OvtA, W Briimrner, Angew. Chem. 84, 319 (1972); Angew. Chem.
Int. Ed. Engl. 11,249 (1972); cf. also Nachr. Chem. Tech. 2 1 , 236 (1973).
[2] a) C . Talsky, Angew. Chem. 83, 553 (1971); Angew. Chem. Int. Ed.
Engl. 10, 548 (1971); b) C . Talsky, W Klunker, 2. Physiol. Chem. 348,
1372 (1967).
131 I . W Sizer, J . Bacteriol. 4 1 , 511 (1941).
[4] H . H . Weetall, R . A. Me.sing in M. L. Hair: The Chemistry of Biosurfaces,
Vol. 2. Dekker, New York 1972, pp. 563ff.
Angew. Chem. Inr. Ed. Engl. 16 (1977) No. I0
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