BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 7. ENZYMOLOGY

7.7. Regulation of Metabolic Processes

7.7.2. Principles of Regulation of Metabolic Pathways

All Chemical Reactions in The Cell occur with the participation of Enzymes. To influence The rate of a metabolic pathway, it is sufficient to regulate the amount or activity of its enzymes. Metabolic pathways contain Key Enzymes that govern the rate of the entire pathway. These enzymes (one or more in a pathway) are called regulatory enzymes; they typically catalyze the initial reactions of a metabolic pathway, irreversible reactions, rate-limiting steps (the slowest ones), or reactions at metabolic branch points.

The regulation of Enzyme Reaction Rates is carried out at three independent levels:

✵ alteration in the number of enzyme molecules;

✵ availability of substrate and coenzyme molecules;

✵ Modification of the catalytic activity of the enzyme molecule.

Regulation of the number of enzyme molecules in the cell. It is known

that cellular Proteins undergo continuous turnover. The number of enzyme molecules in a cell is determined by the balance between two processes — the Synthesis and degradation of the protein molecule of the enzyme:

Protein Synthesis AND folding is a multi-step process. The Regulation of Protein Synthesis can occur at any stage of protein molecule formation. The most thoroughly studied mechanism of protein synthesis regulation operates at the transcriptional level, mediated by specific metabolites, Hormones, and a range of biologically active molecules.

As for enzyme degradation, the regulation of this process is less understood. One can only assume that this is not merely a simple process of proteolysis (The breakdown of a protein molecule), but rather a complex mechanism, likely genetically determined.

Introduction/15.html">Regulation of enzyme reaction rate by the availability of substrate and coenzyme molecules. An important parameter controlling the progression of a metabolic pathway is the presence of substrates, primarily the initial substrate. The higher the concentration of the starting substrate, the greater the rate of the metabolic pathway.

Another parameter that limits the progression of metabolic pathway reactions is the availability of regenerated Coenzymes. For example, in dehydrogenation reactions, the oxidized forms of NAD+, FAD, and FMN serve as coenzymes for dehydrogenases, becoming reduced As a result of the reaction. For coenzymes to participate in subsequent reactions, their regeneration is required, meaning their conversion back into the oxidized form.

Regulation of the catalytic activity of enzymes. The most critical mechanism for altering the rate of metabolic pathways is the regulation of the catalytic activity of one or more key enzymes within a given pathway. This represents a highly efficient and rapid method of Metabolic control.