Enzymatic chemical reactions complete enzyme dependence

The great majority of chemical reactions that occur within the cell are enzymatically catalyzed reactions. These may be called complete enzyme-dependent reactions since the entire reaction depends primarily on the enzyme. We will not consider the general enzymatic reaction any further here since it is treated in Chapters 3 and 4. Less well appreciated are the partial enzyme-dependent reactions, an example of which is the enzymatically mediated photochemical reaction. Here, in addition to the enzyme, energy from a radiation source is necessary for the chemical reaction to occur. Table 2 lists examples of several such reactions. 

The mechanism of an enzymatic reaction is ultimately defined when all the intermediates, complexes, and conformational states of the enzyme are characterized and the rate constants for their interconversion are determined. The task of the kineticist in this elucidation is to detect the number and sequence of these intermediates and processes, define their approximate nature (that is, whether covalent intermediates are formed or conformational changes occur), measure the rate constants, and, from studying pH dependence, search for the participation of acidic and basic groups. The chemist seeks to identify the chemical nature of the intermediates, by what chemical paths they form and decay, and the types of catalysis that are involved. These results can then be combined with those from x-ray diffraction and NMR studies and calculations by theoretical chemists to give a complete description of the mechanism. 

---