Molecular Biology: Protein Structure and Function - Stepanov V.M. 2005

Enzymes

METABOLISM would be impossible without a dramatic acceleration of the reactions it is based on, and without the temporal and spatial coordination of numerous biochemical processes—in other words, without the participation of biological catalysts known as Enzymes. Biocatalytically accelerated transformations encompass a vast array of processes, including those that, from the perspective of classical chemistry, might seem not to require catalysis at all. For instance, the spontaneous dehydration of carbonic acid to form СО₂ is far too slow to regulate Blood pH; therefore, this seemingly simple reaction is catalyzed by a specific enzyme, Carbonic anhydrase.

As is well known, catalysts do not initiate reactions; rather, they accelerate the attainment of equilibrium by increasing the rates of both forward and reverse transformations. Like any catalysts, enzymes speed up biochemical reactions by lowering the activation energy—the energy barrier that separates one state of a system (starting Materials) from another (reaction products). Strictly speaking, this process slightly alters the reaction pathway. The difference in efficiency between enzymes and conventional chemical catalysts might seem to be purely quantitative. For example, the activation energy for the decomposition of hydrogen peroxide into oxygen and Water

Н₂О₂ → Н₂О + 1/2 О₂ is 18 kcal/mol, finely dispersed platinum lowers it to 12 kcal/mol, and the enzyme catalase reduces it to 5.6 kcal/mol, accelerating the reaction by 6 and 12 orders of magnitude, respectively. Such remarkable catalytic efficiency determines The Role of enzymes as the master regulators of biochemical processes. Indeed, thanks to the catalytic action of enzymes, the Organism can drive reactions that, in the absence of efficient catalysis, would be imperceptible within any reasonable observation timeframe.

Thus, enzymes effectively create and enable numerous substance transformations that would be unthinkable without biocatalysis. Moreover, an enzyme often accelerates only one of several thermodynamically feasible reaction pathways, thereby selecting it. Consequently, enzymes act not only as accelerators, but also as unique organizers of metabolic processes, a function further enhanced by The ability to regulate their activity.

The role of biocatalysis was uncovered back in the nineteenth century during The Study of Fermentation processes. Fermentation gave rise to both terms commonly used in literature for biocatalysts: enzyme and ferment. Among these synonyms, the latter is predominantly used in Russian-language literature, alongside the terms enzymology and enzymatic. While enzymes are fundamentally proteinaceous in nature, the ability of certain RNA forms to catalyze reactions—effectively acting as enzymes—has also been discovered. It is hypothesized that this capability of RNA molecules played a crucial role in the evolution of biocatalysis before the Enzymatic Function was transferred to Proteins, which are Biopolymers far better suited for this task.

In many cases, a protein molecule utilizes non-protein compounds during biocatalysis known as Cofactors, particularly Metal Ions that serve as Components of the enzyme's catalytic center. The dissociation of such cofactors, which are typically non-covalently bound to the protein, yields apoenzymes, whereas the complete complex of the enzyme and its cofactor is referred to as a holoenzyme.