Biochemistry - The Chemical Reactions of Living Cells Volume 2 - D. Metzler 1980

Enzymes: Cellular Protein Catalysts

The functional apparatus of Cells consists primarily of Enzymes. Hundreds of enzymes have been isolated from living cells, purified, and crystallized. Many others are identified solely by their catalytic activity and have not yet been isolated in pure form. Most currently known enzymes are soluble Globular Proteins, although structural proteins within The Cell can also exhibit catalytic properties. For instance, Actin and Myosin jointly catalyze the Hydrolysis of ATP (Chap. 4, Sec. E). (It should be noted, however, that it remains unclear how this enzymatic reaction is coupled with the contraction of Muscle fibers.)

The METABOLISM/8.html">Properties of Enzymes—protein catalysts—are covered by an extensive body of literature, and a newcomer to this field might not even think to ask a series of simple yet critically important questions. How do we know that a cell is "packed" with enzymes? How do we determine whether a given protein is an enzyme? The answer is that enzymes are identified exclusively by their ability to catalyze Chemical Reactions. Consequently, measuring enzyme catalytic activity is a routine daily Procedure for many biochemists. These remarkable molecules can only be isolated and purified by carefully measuring the rates of the reactions they catalyze.

Enzyme kinetics, which deals with the quantitative study of enzyme-catalyzed reactions, is a field where mathematical Methods have found the widest application and holds immense practical value for the biochemist. It is our most powerful tool for elucidating catalytic mechanisms. Kinetic studies make it possible to determine the affinity of substrates and inhibitors for enzymes and the Specificity of their binding, to find the maximum velocity of processes catalyzed by specific enzymes, and to address many other problems.

The Basic Concepts of enzyme kinetics and some experimental data are briefly outlined below. Note that the primary objective of kinetic studies is to derive a rate equation that relates the reaction velocity to experimentally measurable parameters. For a more thorough exploration of this topic, the reader should consult specialized articles and books, such as [1–5]¹⁾.

¹⁾ Among recently published books, the following can be recommended: Cornish-Bowden A., Fundamentals of Enzyme Kinetics, London, Butterworths, 1979; Berezin I. V., Martinek K., Fundamentals of Physical Chemistry of Enzymatic Catalysis, Moscow, Vyshchaya Shkola, 1977 (in Russian); Roberts D. V., Enzyme Kinetics, Cambridge University Press, Cambridge, 1977; Marmasse C., Enzyme Kinetics, Gordon and Breach, New York, 1977; Ainsworth S., Steady-State Enzyme Kinetics, Macmillan Press, London, 1977. — Transl. note.