Kinetic studies of the urease-catalyzed hydrolysis of urea in a buffer-free system |
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Authors: | Yingjie Qin Joaquim M S Cabral |
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Institution: | (1) Laborat’orio de Engenharia Bioqu’imica, Institute Superior T’ecnico, 1000 Lisboa, Portugal |
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Abstract: | The kinetics of urea hydrolysis catalyzed by urease, mainly in the absence of buffers by use of the self-buffer effect of
the products, was investigated. The effect of pH, temperature, and concentration of enzyme, substrate, product, salt ions,
and buffers on the kinetic behavior of urease was examined. A kinetic model of a modified Michaelis-Menten form, incorporating
substrate and product inhibition, pH dependence, and temperature effect, was developed to describe the reaction rate. Experimental
data indicated that urease in a buffer-free solution was less susceptible to the inhibition of substrate product. The Michaelis
constant keeps almost constant with the variation of pH and temperature, and increases with the addition of buffers and salts.
The data also suggested that the noncompetitive pattern of the product inhibition, which is not significantly affected by
temperature, increases gently with increasing pH. A Monod form rate expression was proposed to analyze the pH effect on the
maximum rate. The proposed kinetic model was also examined by the long-time experiments in which pH, substrate, and product
concentration varied obviously during the reaction course. |
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Keywords: | Enzyme kinetics soluble urease urea hydrolysis buffer-free system pH control by CO2 addition |
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