Lecithin is an important biologically active molecule that has many basic physiological functions in the human body, such as the main component of cell membranes, neurotransmitters, and lipid metabolism in the liver, so it is very meaningful to understand its synthesis. In this article, all the synthesis routes of Lecithin will be introduced from the following aspects: phosphatidylcholine synthesis pathway, lecithin synthesis pathway, phospholipid synthesis pathway and fatty acid glycerol phosphate synthesis pathway.
1. Phosphatidylcholine synthesis pathway:
Lecithin, also known as lecithin, is an important phospholipid substance widely present in animal and plant organisms. In organisms, Lecithin plays a variety of important physiological functions, including cell membrane structure, neurotransmission, cholesterol metabolism, etc.
Phosphatidylcholine is one of the most important components of Lecithin, which is quite abundant in the human body. The biosynthesis of phosphatidylcholine is generally completed through a methyl transfer reaction, and its detailed route is as follows:
1.1. Phosphatidylacyldiacylglycerol (PA) formed from fatty acids and glycerol is phosphorylated by CDP-acylcholine (CDP-Choline) to generate phosphorylcholine (PtdCho).
1.2. At the same time, methylation is provided by SAM (S-adenosylmethionine) to methylate methionylcholine (GPC) into fat-2-phosphoadenosylcholine (PC).
1.3. PtdCho and PC generate phosphatidylinositol choline (PI-Cho) through the exchange reaction catalyzed by fat-1-phosphoinositide transferase.
1.4. PI-Cho is then converted into phospho-inositol choline (IP-Cho) by dephosphorylation.
The above is the total synthesis route of phosphatidylcholine, in which the first and second steps are the phosphorylcholine pathway (Kennedy pathway), which mainly occurs in the endoplasmic reticulum and Golgi body; the third and fourth steps are inositol phospholipids pathway, mainly in the cytoplasm and in eosinophilic bodies. The synthesis of phosphatidylcholine requires the participation of various enzymes and coenzymes, such as CDP acylase, SAM adenylase, phosphatidylinositolase, and dephosphatase.
2. Lecithin synthesis pathway:
Lecithin is an important biological lipid that widely exists in organisms, and has important functions in the maintenance of cell membrane structure and function, neurotransmission, and lipid metabolism. Its main components include phosphorylcholine, phosphorylacetylcholine, and phosphorylcreatine, among which phosphorylcholine has the highest content, accounting for more than half of the total amount of lecithin. The synthesis process of lecithin involves multiple metabolic pathways and the synergy of various enzymes, which are different in different cell types and different tissues. The main synthesis pathway of lecithin will be discussed below.
2.1. Glycerophosphate pathway (GPAT pathway):
The glycerophosphate pathway is the initial step of lecithin synthesis, and its process mainly includes the following steps: glycerol triphosphate (G3P) combines with fatty acids to generate acyl glycerophosphate (LPA), and LPA further generates phosphatidic acid (PA) through decarboxylation reaction, PA Reduction produces CDP-acylglycerol (CDP-DAG), and CDP-DAG and choline, ethanolamine and other substrates further synthesize lecithin through the inositol phospholipid pathway. GPAT enzyme is the rate-determining enzyme of the glycerol phosphate pathway, and its catalysis is to acylate glycerol triphosphate and fatty acid to generate LPA. The supply of substrates such as choline must be carried out through one of the two pathways of "inositol phosphatidylation" and "ornithine phosphatidylation".
2.2. Inositol phospholipid pathway:
The inositol phospholipid pathway is one of the important synthesis pathways of lecithin, and its pathway is related to the cell membrane diphosphate mannitol pathway. The synthesis of inositol phospholipids mainly includes the following two steps: phosphatidylation reaction of choline or inositol phosphate with acylglycerol phosphate to generate phosphoglycerol choline (PGC) or phosphoglycerol inositol (PGI), and then through inositol Phosphoglycerol transferase (PIT) and phosphoglycerol transferase (PGT) transfer phosphoglycerol choline or phosphoglycerol inositol to the CDP-DAG molecule to form a complete lecithin molecule. The phosphorylcholine synthesized by the inositol phospholipid pathway accounts for about 20% of the total amount of lecithin.
2.3. Ornithine phospholipid pathway:
The ornithine phospholipid pathway is the main pathway for the synthesis of ornithine phospholipids. This pathway relies on the hydrolysis of ornithine in the cell to ammonia and the catalysis of carbon dioxide to generate pyruvic acid and oxalic acid, and then the acyl transfer reaction of oxalic acid and acylglycerol phosphate to obtain phosphoglyceryl oxalic acid (PGS). Subsequently, PGS transfers the phosphorus group to the CDP-DAG molecule through two enzyme-catalyzed reactions (PSD and PSS), generating a complete lecithin molecule. The phosphorylcholine synthesized by the ornithine phospholipid pathway accounts for about 10% of the total amount of lecithin.
3. Synthesis pathway of phospholipids:
Lecithin (phospholipid) is a very common phospholipid, its main components are phosphoglycerides and choline, and can be widely used in food, medicine, pesticides and other fields. There are many preparation methods of Lecithin, the most commonly used ones are chemical methods and biological methods.
The specific process is as follows:
1. Cafestol and Amino Acids:
In the industrial fermenter, the cell substrate cafestol and amino acid are added, and after fermentation reaction, a fermentation liquid containing cafestol and amino acid is generated.
2. Phosphorylation:
Add an appropriate amount of phosphoric acid to the fermentation broth, and use phosphorylase to add phosphoric acid to glycerol to form glycerophosphate. Among them, the function of phosphorylase is to add phosphoric acid to cafestol and amino acids.
3. Generate fatty acid ethanolamine:
Glycerophosphate and fatty acid ethanolamine are reacted by acylase to form Lecithin. Among them, the function of acylase is to combine fatty acid with phosphoglyceride or alcohol amine to form Lecithin.
4. Enzyme immobilization technology:
The technology allows large quantities of enzymes to be produced and can be reused, making the process of producing Lecithin more cost-effective. The enzyme is immobilized on kaolin to transfer fatty acid groups to ethanolamine to form Lecithin, which has good reusability.
Phospholipid is one of the most important components of Lecithin, and its synthesis pathway involves different substrates. Phosphoric acid (pentose phosphate pathway) is the substrate 1-hydroxyglyceric acid produced by sugar metabolism; substrate phosphatidic acid is produced by acidification; CDP-choline can be obtained by methylation reaction; The substrates pyruvate and methylvalonate are produced; the amino acids lysine and leucine can be obtained by decarboxylation; the substrates potassium and methionine can be used as the reaction substrates that catalyze the two-in-one reaction of CDP choline phosphate.
4. Synthesis pathway of fatty acid glycerol phosphate:
Fatty acid glycerol phosphate synthesis pathway is another pathway for the biosynthesis of Lecithin, in which there is no choline, its main substrates are fatty acids and tartrate, and triglyceride can be obtained by the catalysis of acyl inarcosyl synthase. Subsequently, through the action of triglyceride acyltransferase, a phosphate bond is formed between 2-hydroxyglycerol and tartrate to form the molecular structure of fatty acid glycerol phosphate, which is the precursor of Lecithin.
In summary, the synthetic pathways of lecithin include phosphatidylcholine synthetic pathway, lecithin synthetic pathway, phospholipid synthetic pathway and fatty acid glycerol phosphate synthetic pathway. Among them, the phosphatidylcholine synthesis pathway and the lecithin synthesis pathway are similar to each other, and both react through the CDP-chloroacetic acid intermediate; the phospholipid synthesis pathway uses more substrates, including substrates produced by sugar metabolism and oxidation pathways. Substrates and substrates produced by decarboxylation reactions; the main function of the fatty acid glycerol phosphate synthesis pathway is to form the precursor molecular structure of Lecithin.