Liubinskiĭ G V, Ianishpol'skiĭ V V, Tertykh V A, Iuodval'kite D Iu, Glemzha A A
Ukr Biokhim Zh (1978). 1982 Mar-Apr;54(2):145-8.
The paper deals with kinetics of the urea hydrolysis by microbial-origin urease dissolved and immobilized on the organic silica surface. It is shown that hydrolysis kinetics for soluble urease is described by the Michaelis-Menten equation until the concentration of urea reaches 1 M. Two fractions differing in the Michaelis constant are revealed for silochrome immobilized urease. The rate of urea hydrolysis by native and immobilized urease was studied depending on the pH value in presence of the substrate in the 1 M and 5 mM concentration. The hydrolysis rate of 1 M urea in the buffer-free solution by silochrome-immobilized urease is practically independent of pH within 4.5-6.5. Application of a 2.5 mM phosphate-citrate buffer as a solvent causes an increase in the hydrolysis rate within this pH range. For a soluble urease the 1 M urea hydrolysis rate dependence on pH is ordinary at pH 5.8-6.0. If the substrate concentration is 5 mM, the pH-dependences for the rate of the urea hydrolysis by silochrome- and aerosil-immobilized urease are close and at pH above 6.0 coincide with those for a soluble enzyme. The found differences in the properties of soluble and immobilized ureases are explained by the substrate and reaction products diffusion.
本文研究了溶解并固定在有机硅表面的微生物源脲酶催化尿素水解的动力学。结果表明，在尿素浓度达到1 M之前，可溶性脲酶的水解动力学可用米氏方程描述。对于硅铬固定化脲酶，发现了两个米氏常数不同的组分。研究了天然脲酶和固定化脲酶在1 M和5 mM浓度底物存在下，尿素水解速率随pH值的变化。在无缓冲溶液中，硅铬固定化脲酶对1 M尿素的水解速率在4.5 - 6.5范围内实际上与pH无关。使用2.5 mM磷酸 - 柠檬酸盐缓冲液作为溶剂会使该pH范围内的水解速率增加。对于可溶性脲酶，1 M尿素水解速率对pH的依赖性在pH 5.8 - 6.0时是正常的。如果底物浓度为5 mM，硅铬和气相二氧化硅固定化脲酶催化尿素水解速率的pH依赖性相近，且在pH高于6.0时与可溶性酶的情况一致。可溶性脲酶和固定化脲酶性质上的差异是由底物和反应产物的扩散所解释的。
