Fundamentals of Biochemistry - Filippovich Yu. B. 1999

Coenzymes, vitamins, and certain other bioactive compounds
Coenzymes

The Chemical Nature of Coenzymes is extremely diverse. They include organic substances belonging to the aliphatic and aromatic series, as well as heterocyclic compounds, both mono- and polynuclear. A single physicochemical description cannot be applied to coenzymes, as they represent a miscellaneous group of compounds united by only one common feature: The ability to bind with protein apoenzymes to form catalytically active holoenzymes.

The term "coenzyme" was first introduced in 1897 when G. Bertrand, while studying The properties of lactase (β-galactosidase, which cleaves terminal non-reducing residues in β-galactosides), used it to designate an activator of this enzyme, namely Mn²⁺. The next major milestone in The Development of coenzyme research was the work of British biochemists A. Harden and W. Young, who in 1906 proved the presence of a heat-stable factor separable by ultrafiltration—cozymase—in Yeast zymase enzyme preparations.

Among Enzymes that require coenzymes as obligatory partners in catalytic reactions, 675 (nearly 85%) utilize nucleotide-based compounds for this purpose: NAD⁺ (~165 enzymes), NADP⁺ (~155), both NAD⁺ and NADP⁺ (~50), coenzyme A (~80), and ATP (~225). These constitute the largest group of so-called nucleotide coenzymes. Pyridoxal phosphate is an equally widespread coenzyme; its role in Transamination reactions was discussed earlier (see p. 127), and its function in AMINO ACID DECARBOXYLATION processes will be covered later (see p. 267). In A number of enzymes, FMN and FAD, as well as quinoid compounds, serve as coenzymes. The chemical nature and Functions of these coenzymes in catalytic processes are described in Chapter III.

Other Organic compounds also function as coenzymes. For instance, Lipoic Acid, Glutathione, and iron-Porphyrins act as coenzymes in redox reactions, nucleoside diphosphate sugars in The transfer of glycosyl residues and their derivatives, and cytidine diphosphate Choline in the transfer of nitrogenous bases during phospholipid Biosynthesis, and so on. The mechanisms of their involvement in enzymatic processes are discussed in subsequent chapters. In addition, many Vitamins perform coenzyme functions.