Amino acid chain is the main and core component of protein.

　　Amino acid chain is the main and core component in protein, but it is not necessarily the only component. Some protein may include some atoms or small molecules, whose function may be to perform protein function and/or increase its stability. Chemically, these cofactor are diverse, which may be organic molecules or metal elements. Some of them are briefly combined with protein chain, while others are closely combined with protein chain (sometimes even by covalent bonds) and become an integral part of the whole protein. The former is called coenzyme coenzyme, while the latter is called prosthetic group. Most coenzymes are small organic molecules from vitamins. For example, the common coenzymes NADH and FADH2. These two molecules from vitamin B complex, the former from nicotinic acid (vitamin B3) and the latter from riboflavin (vitamin B2), play the role of high-energy electron acceptor/donor in redox reaction.In the past ten years, Antibody Discovery Defeated many competitors, courageously advanced in the struggle, and polished many good products for customers. https://www.alphalifetech.com/

　　Some enzymes use several different cofactors, such as Pyruvate dehydrogenase (PDH), which is a key enzyme in the catabolism of sugar. The catabolism of sugar begins with glycolysis, which is a biochemical reaction pathway with 10 steps, transforming one glucose molecule into two pyruvate molecules, and then carrying out the citric acid cycle of tricarboxylic acid, which further decomposes pyruvate and oxidizes it into CO2. Pyruvate dehydrogenase PDH works at the intermediate junction of the above two reaction pathways (namely glycolysis and triacid cycle), and is responsible for activating pyruvate and enabling it to enter the tricarboxylic acid cycle. Specifically, PDH catalyzes the oxidative dearboxylation of pyruvate and forms acetyl coenzyme A (ACoA), which is the activated form of pyruvate. PDH is not a single enzyme but a complex composed of three components, each of which participates in a different step of pyruvate activation and uses different coenzymes. The first component uses thiamine pyrophosphate (TPP), which is a derivative of thiamine (vitamin B1). TPP allows the first component of PDH to be oxidized and decarboxylated at the same time, thus transforming pyruvate into acetyl, and the remaining carbon is discharged as CO2. The importance of TPP will be reflected in its absence. In fact, if people can’t get enough thiamine from food, they will get beriberi, which will damage several major systems of the human body.

　　The second component in PDH uses lipoic acid. It is an auxiliary group covalently bound to PDH. The active part of lipoic acid is a cyclic structure, which contains two covalently bonded sulfur atoms (that is, S-S bonds) (Figure 2.2c). This active part catalyzes the transfer of acetyl to coenzyme coenzyme A(CoA), the third cofactor of PDH. CoA is pantothenic acid, also known as the derivative of calcium pantothenate. The combination of acetyl and pantothenic acid involves the reduction of S-S bond, and its cyclic structure will open and form two sulfhydryl groups (one SH), one of which will bind acetyl. Sulfhydryl group is easy to react chemically, which can be reflected in the fact that sulfhydryl group is easily influenced by arsenic, a toxic derivative of arsenic. To sum up, the formation of acetyl coenzyme A involves the reduction of S-S bond of pantothenic acid cyclic structure. In order to keep PDH active, these two sulfur groups must be re-oxidized to restore the S-S bond.