Kinetic properties and stability of potato acid phosphatase immobilized on Ca-polygalacturonate |
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| Authors: | C Marzadori C Gessa S Ciurli |
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| Institution: | (1) Istituto di Chemica Agraria, Università die Bologna, Viale Berti Pichat, 10, I-40126 Bologna, Italy Tel.: +39-51-259794, Fax: +39-51-259292, IT |
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| Abstract: | Acid phosphatase from potato was adsorbed and immobilized on a pre-formed network of Ca-polygalacturonate, a substrate which
has a composition and morphology similar to the mucigel present at the root-soil interface. The influence of different types
of organic buffers on enzyme adsorption and activity was investigated. The highest enzyme activity, for free and adsorbed
enzyme, was obtained with Na-maleate buffer at pH 6.0, which was used for all subsequent experiments. The Michaelis-Menten
kinetic parameters, Vmax and Km, were determined for free and adsorbed phosphatase. Vmax showed a 60% decrease upon adsorption (2.09±0.30 U/mg, for the soluble form and 0.84±0.15 U/mg, for the adsorbed enzyme),
whereas Km increased from 0.49±0.15 mM for the free enzyme to 0.99±0.20 mM for adsorbed phosphatase. Phosphatase adsorption decreased
as the concentration of NaCl increased, indicating that the enzyme is bound to the carrier gel through coulombic interactions.
Adsorption increased stability of the enzyme as compared with the free enzyme (t
1/2 of the activity was 9.4 days and 5.8 days, respectively), but increased thermal and proteolytic inactivation. The pH/activity
profile revealed no change in terms of shape or optimum pH (4.5) upon adsorption of the enzyme. These results indicate that
adsorption of acid phosphatase on Ca-polygalacturonate induces changes in the kinetic properties and stability of the enzyme,
and the same type of response can be extrapolated from these results for acid phosphatases of the rhizosphere.
Received: 1 July 1997 |
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| Keywords: | Potato acid phosphatase Ca-Polygalacturonate Rhizosphere Mucigel Michaelis-Menten kinetics |
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