Biochemistry

соон I CH I COOH COOH Лён FT + H.o + « CH (Н++ОН-) COOH COOH I fH-OH CH, I - COOH Fumaric acid Activated form of fumaric acid Apple acid The double bond present in fumaric acid is represented by electron pairs. During the interaction of fumaric acid with fumarase, the formation of an enzyme ­ substrate complex occurs, as a result of which the functional groups of the active center of the enzyme contribute to the redistribution of the double bond electrons. As a result of this, one of the carbon atoms acquires an electron and is negatively charged, and the other, giving up the electron, positively. Thus, the fumaric acid molecule becomes activated and can easily attach H + and OH - ions (water ions) in the form of an electrostatic bond and turn into malic acid. Two processes simultaneously occur in the enzyme-substrate complex', a change in its electron density ’ , which causes polarization of the bonds, as well as geometric deformation (stress) of individual bonds both in the substrate molecule and in the active center of the enzyme. These processes contribute to overcoming the activation barrier of the transition state of the enzyme-substrate complex. In the first phase of enzymatic catalysis, a compound is formed between the substrate and the enzyme in which the reactants are linked to each other by a covalent or ionic bond. In the second phase, the substrate under the influence of the enzyme attached to it changes and becomes more accessible for the corresponding chemical reaction. In the third phase, the chemical reaction itself occurs and, finally, the resulting reaction products in the fourth phase are released from the enzyme ­ substrate complex. If the enzyme is denoted by the letter F, the substrate is S, the activated substrate is Si, and the reaction product is P, then this process sequence can be expressed as follows: I II ПІ IV F + S «-> FS <-> FS t <-> FP «-> F + P The enzyme binds to the substrate in a reversible reaction with the formation of the enzyme-substrate complex. In the process of the formation of the latter and in the subsequent stages of enzymatic catalysis, repeated changes in the tertiary 90