Common vitamins and corresponding coenzymes

Thiamine
That is, vitamin B1. Its coenzyme form in the body is thiamine pyrophosphate (TPP) (Figure 1 [Structural formula of thiamine pyrophosphate (TPP)]).
Thiamine pyrophosphate was formerly known as a decarboxylase. It plays an important role in animal glucose metabolism, such as in the decarboxylation of pyruvate. In the absence of TPP, the metabolic intermediate pyruvate cannot be decarboxylated smoothly and accumulates in the blood and tissues, leading to symptoms of neuropathy. TPP is also a coenzyme for other enzymes such as ketoacid oxidase and transketolase. The enzyme reaction catalyzed by TPP also requires the presence of magnesium ions.
nicotinamide
It is a precursor of coenzymes for a series of enzymes.
It has long been known that niacinamide can prevent pellagra. In 1904, it was known that alcohol fermentation cannot be without a substance called coenzyme I. In 1933, this coenzyme I was isolated. In 1934, German biochemist O. Warburg isolated a substance similar to coenzyme I, called coenzyme II, and confirmed that nicotinamide is a component of these two coenzymes. It has been clarified that the chemical composition of coenzyme I is nicotinamide adenine dinucleotide (NAD), and the chemical composition of coenzyme II is nicotinamide adenine dinucleotide phosphate (NADP).
Enzymes that use NAD and NADP as coenzymes are called pyridine nucleotide (or nicotinamide nucleotide) linked dehydrogenases. These enzymes catalyze redox reactions within cells. Generally speaking, dehydrogenases associated with NAD are usually related to respiratory processes, while those associated with NADP are related to biosynthetic reactions.
Coenzyme I
(NAD)
The chemical name is nicotinamide adenine dinucleotide or nicotinamide diphosphate, which exists in two states in mammals: oxidized (NAD+) and reduced (NADH). It is an important coenzyme in human redox reactions. Meanwhile, it is the only substrate for NAD+- dependent ADP ribosyltransferase, which can be classified into three types in vivo: 1. ADP ribosyltransferase or poly ribosyltransferase (PARP); 2. Cyclic ADP ribose synthase (cADPR synthases); 3. Type III lysine deacetylase Sirtuins. These enzymes break down coenzyme I (NAD+) as a substrate into ADP ribose and nicotinamide (Nam), and perform different physiological functions in different cells [3].
Riboflavin
Vitamin B2 is involved in the formation of two coenzymes, which are the main components of the intracellular redox system. They are flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD).
FMN and FAD are a series of flavin linked oxidoreductases or coenzymes called flavoproteins, which can also be considered as cofactors based on their tight binding to enzyme proteins. Some of these enzymes require metal cofactors such as iron or molybdenum ions in addition to FMN or FAD. Therefore, they are called metalloflavoproteins. These enzymes catalyze a series of reversible or irreversible redox reactions in cells.
Pyridoxal
Pyridoxal, pyridoxamine, and pyridoxine are collectively referred to as vitamin B6 (structural formula "class=image" in Figure 3 [Structural Formula of Vitamin]). Vitamin B6 participates in the formation of two coenzymes, namely pyridoxal phosphate and pyridoxamine phosphate.
Enzymes that require pyridoxal phosphate or pyridoxamine phosphate as coenzymes are particularly important in amino acid metabolism, catalyzing transamination, decarboxylation, and racemization.
lipoic acid
Lipoic acid exists as a mixture of two structural forms: closed ring disulfide and open chain reduction. These two forms can be converted into each other through an oxidation-reduction cycle. It generally does not exist freely, but rather covalently binds to the ε - NH2 group of lysine residues in its carboxyl group with enzyme molecules (such as dihydrolipoic acid acetyltransferase) through amide bonds. The enzyme that catalyzes the formation of thioamide bonds requires the participation of ATP. Lipoic acid is an acyl carrier that serves as a coenzyme for pyruvate dehydrogenase and glycine decarboxylase. It exists in pyruvate dehydrogenase and alpha ketoglutarate dehydrogenase and plays a role in coupling acyl and electron transfer during alpha ketoacid oxidation and decarboxylation.
Lipoic acid can play an antioxidant role in water-soluble and water-insoluble environments, enhance the absorption of glucose by animal skeletal muscle and red blood cells, improve glucose metabolism, protect nerve cells in diabetes patients, and reduce the incidence of neuropathy. In addition, it also has certain benefits for other chronic diseases such as cardiovascular disease, liver and kidney disease, and has a certain therapeutic effect on neurological disorders caused by alcohol (ethanol) or chemical toxic substances. [5]
biotin
Plays a cofactor role as a cofactor for some enzymes. It is covalently linked to a specific lysine residue of the deubiquitin protein through an amide bond and an ε - amino group. ε - N-biotinyl-L-lysine is called biotin.
Enzymes that require biotin can catalyze the incorporation (carboxylation) or transfer of carbon dioxide, thus the fixation of biotin and carbon dioxide is closely related. Adenosine triphosphate (ATP) and magnesium ions are also required for carboxylation, and biotin plays an important role in protein biosynthesis and transamination.
pantothenic acid
Originally isolated as a growth factor for yeast. Due to its widespread presence in organisms, it is called pantothenic acid. The coenzyme form of pantothenic acid is coenzyme A (CoA or CoASH), which is an auxiliary factor in enzymatic acetylation. Its biological importance lies in its role as a carrier or donor of acyl groups, particularly in the metabolism of fatty acids.
folic acid
Because it was first isolated from spinach leaves, it is named.
The coenzyme form of folate is tetrahydrofolate, which serves as an intermediate carrier for enzymatic transfer of one carbon groups (such as formyl groups) and plays a role in the biosynthesis of purine, serine, glycine, and methyl groups. In addition, folate is also indispensable in the biosynthesis of nuclear proteins.
Vitamin B12
In the 1920s, it was discovered that feeding patients with animal liver could treat pernicious anemia, indicating that there is a factor in the liver that is effective in treating pernicious anemia. Vitamin B12 has been isolated and purified, and its structure has also been clarified. Vitamin B12 has a corrin ring system in its structure and contains cobalt ions and a cyanide group (CN), hence it is also known as cyanocobalamin. Pure vitamin B12 solution appears red, which is also a characteristic of typical cobalt compounds. When used as a coenzyme, the CN in vitamin B12 is replaced by a 5 '- deoxyadenosine group, which is called coenzyme B12. This is an unstable compound that transforms into vitamin B12 when cyanide is present or exposed to light. If 5 '- deoxyadenosine group is used instead of the blackbody CN group in the formula, it is the structural formula of coenzyme B12.