Enzyme-dependent responses of stimuli-sensitive systems.

The methods of creating of systems where properties depend both on an outer physical signal and enzyme activity are discussed. The construction of a conjugation chain between responses of stimuli-sensitive materials and urea hydrolysis catalyzed with urease is demonstrated on the basis of light- and thermoreversible polymeric matrices.

Effect of thermosensitive matrix-phase transition on urease-catalyzed urea hydrolysis.

Temperature dependencies of kinetic and equilibrium parameters of urea hydrolysis catalyzed by native urease and the urease immobilized in a thermosensitive poly-N-isopropylacrylamide gel have been studied. The swelling ratio of the collapsed urease-containing gel is shown to increase in the presence of urea. Below a lower critical solution temperature (LCST) of the polymer, the immobilized urease actually has the same catalytic properties as the native enzyme. At temperatures above LCST, the observed catalytic activity of the immobilized enzyme depends chiefly not only on the thermoreversible matrix state, but also on gel water content.

Relationship between state of a thermosensitive matrix and the activity of urease immobilized in it.

The effect of temperature on kinetic and equilibrium parameters of urea hydrolysis catalyzed with urease immobilized into a thermosensitive poly-N-isopropylacrylamide gel was studied. The temperature behavior of the gel-urease system is different from similar systems. After a decrease in the enzyme activity above the critical temperature, the maximal rate of the enzymatic reaction and gel swelling ratio begin to increase. Urea hydrolysis catalyzed with immobilized urease and shrinking-swelling of the thermosensitive urease-containing gel depend on each other. Under collapse, gel swelling increases due to the enzymatic reaction. The rate of the enzymatic reaction no longer follows Michaelis-Menten kinetics, and the dependence of the reaction rate on substrate concentration becomes more complicated.