BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 7. ENZYMOLOGY

7.1. General characteristics of enzymes as biological catalysts

7.1.2. Catalytic efficiency

Most enzyme-catalyzed reactions are highly efficient, proceeding 10⁸-10¹⁴ times faster than non-enzymatic reactions. Each enzyme molecule is capable of transforming from 100 to 1000 substrate molecules into product per second. The number of substrate molecules converted into product by a single enzyme molecule per 1 s is referred to as the turnover number, or molar activity.

The catalytic efficiency of an enzyme, like that of any other protein molecule, depends on its conformation, particularly the conformation of its Active Site. Enzymes are characterized by conformational lability—The ability to undergo minor changes in native conformation due to the disruption of weak bonds. Therefore, METABOLISM/18.html">The Influence of Denaturing Agents capable of altering the enzyme conformation leads to A change in the active site conformation and a decrease in the ability to bind the substrate. As a result, the catalytic activity of the enzyme diminishes.

Enzyme activity in The Cell depends on the concentration of substrate and product molecules, as well as the presence of Cofactors and Coenzymes. The action of enzymes within the cell is typically tightly regulated: the product of one enzymatic reaction serves as the substrate for another, thus forming "metabolic pathways." Among the numerous enzymes in virtually every metabolic pathway, key or regulatory enzymes are distinguished, whose activity can vary depending on the cell's demand for the end product of the pathway. Regulatory enzymes are usually located at the beginning and/or at the branching points of a metabolic pathway. They catalyze either the slowest (rate-limiting) or irreversible reactions.