The characteristics and commonalities of the three methyl donors betaine, methionine, and choline, their metabolic relationships and their mutual substitution. The authors believe that the three substances, methionine, choline and betaine, have their own physiological functions. In this regard, the three are not mutually substitutable, and the diet must contain a certain amount of choline and methionine. However, in terms of methyl donors, the three can replace each other on the basis of their unique physiological functions. Betaine is An effective methyl donor has a significant feed effect. 1. Chemical Structure and Physicochemical Properties of Betaine The chemical name of betaine is 1--carboxyl--NNN--trimethylaminoethyl lactone. CH3 | Structural formula: CH3-N-CH2-COOH | CH3 is a quaternary amine base material, the amount is 117.15, often contains a molecule of crystal water, has both sex, water soluble neutral, white crystal, sweet taste, Its boiling point is 273 °C, easily soluble in water, soluble in methanol, acetic acid, etc., slightly soluble in ether, easily deliquescence, easy to decompose trimethylamine in concentrated strong alkali solution, its hydrochloride is not easy to deliquescence, sugar beet Bases are non-toxic substances. 2. Determination of Betaine Betaine is measured by spectrophotometry (AOAC, 1984) and high performance liquid chromatography (Rajakgla, 1983). Spectrophotometry operations are generally considered to be complicated, the analysis time is long, and the accuracy is poor. High performance liquid chromatography requires only a suitable column, such as amino acid column (Vialle, 1981), sodium cation exchange resin column, differential scanning detector or UV variable wavelength detector (190nm). The method is accurate, rapid and highly reproducible, but the high-performance liquid chromatograph is expensive and there is a certain limit to the promotion of this method. 3. Biological function of betaine 3.1 Betaine as a methyl donor Since methyl is synthetic methionine, carnitine, creatine, phospholipids, epinephrine, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) have the main physiology The role of the necessary substances (Baker et al., 1985; Frontien et al., 1994) and the role of the methylation reaction in the nervous system, immune system, urinary system, and cardiovascular system are considered to be necessary for both growing and adult animals. Stable methyl donor. It is generally believed that the animals themselves cannot synthesize methyl groups and need foods that are rich in methyl groups. They have easily reactable methyl groups in their molecules and thus participate in animal physiological functions. Such methyl-rich substances are called "methyl groups. The donor, which is a methyl group that is easily involved in this reaction (i.e., effective methyl group), is a methyl group linked to a nitrogen atom or a sulfur atom, such as betaine, methionine, and choline (Vogt, 1967). Methionine, gallbladder Alkali and betaine have three different physiological functions. In this respect, the three are not mutually substitutable, but in terms of methyl donors, the three can replace each other on the basis of satisfying their specific physiological functions. However, Shen Tong (1998) reported that some biochemical reactions require different methyl sources. The common role of methionine, choline and betaine is a methyl donor. The synthesis of methionine in animals relies on choline to provide a methyl group, while choline itself does not function as a methyl donor. Choline must be oxidized to betaine in the mitochondria to function as a methyl donor, while betaine can no longer be reduced to choline. Betaine can transfer methyl to homocysteine ​​to synthesize methionine, homocysteine ​​is metabolized by methionine in the body, and the natural protein contains almost no such amino acid, and the newly generated homocysteine ​​can be further transformed. Come to the methyl. During this cycle, there was no new methionine molecule. During this cycle, methionine simply shifted the methyl group provided by betaine to the other reactions. So betaine does not come back to replace methionine synthesis protein, but if the supply of choline or betaine is insufficient, the transmethyl cycle is inhibited because there is not enough methyl group to transfer to homocysteine ​​for methionine synthesis. Therefore, methyl will It has to be provided by methionine, which cannot be regenerated in the diet, thereby weakening the protein synthesis and reducing the utilization of methionine. Cook (1994) believes that if methionine is over-supply and there is a lack of choline and betaine, a large amount of homocysteine ​​accumulates in the body, resulting in humeral cartilage dysplasia and atherosclerosis. This explains why there is enough choline and betaine in the diet to meet the need for unstable methyl groups. In addition, choline needs to be converted to betaine to function as a methyl donor, and betaine cannot be reduced to choline. Tests have shown that betaine, an intermediate metabolite commonly found in animals, is formed by the oxidation of choline with liver fibrinase. This reaction requires the participation of VB12 and is easily inhibited by nickel, cobalt and iron salts. The lack of flavin and the presence of coccidia also inhibited the reaction and affected the performance of choline. The direct use of betaine reduces the oxidation of choline to betaine, so the direct use of betaine will be more effective (Lowry, 1978). From the biochemical pathway of the conversion methyl cycle, it can be seen that when choline is used as a methyl donor, it is converted to betaine, but betaine cannot be reduced to choline, and betaine does not function as other choline functions. In addition, for chicks, choline synthesized from phosphatidylethanolamine and methyl provided by methionine is not sufficient to meet its needs, so chicks have an absolute amount of choline not satisfied by betaine or methionine. 3.2 Metabolism of Betaine and Amino Acids and Proteins Finkelstein et al. (1974; 1982) and Huang Dayou (1983) studied homocysteineuria in humans and found that the addition of betaine can significantly increase the content of methionine in the liver. Xue et al. (1986) found that the methionine cycle in the liver was significantly enhanced in sheep and rats fed betaine. This shows that betaine is closely related to the metabolism of methionine. On the one hand, betaine is more effective than methionine to provide activity. Methyl can reduce the consumption of methionine in the supply of methyl groups. On the other hand, betaine can increase the total activity and specific activity of betaine homocysteine-S-methyltransferase (BHMT) in the liver of animals and promote high levels of The conversion of cysteine ​​to methionine has a net effect of increasing methionine. Feng Jie (1996), Zhou Hongsong (1997) added betaine to finishing pig diets and found that the serum glycine and serine content increased significantly. The reason for this may be the formation of dimethylglycine by betaine after transmethylation and the subsequent demethylation of glycine and serine. Xu Qirong (1997) showed that the addition of betaine to the feed increases the proportion of RNA/DNA in the muscle of the pig longissimus dorsi and broilers, which means an increase in protein synthesis. Wang Yizhen (1998) reported that adding different doses of betaine (600, 1300, 2000, 2700 mg/kg) significantly changed the carcass composition and meat quality of chicks, and the chest muscle rate was significantly improved, with the 2000 mg/kg group being the best. The addition of betaine increased 16.14% (P<0.05). 3.3 Betaine Involved in Fat Metabolism Sandarson (1990), Mekinley (1990), Shette (1993), and Li Xiubo (1995) conducted comparative tests of betaine and choline, respectively, and found that animals fed betaine have lower body fat mass. The distribution of body fat is more uniform, the meat is looser, the taste is delicious, and the meat production of young birds is increased by 3.7%. From Yu Yan (1999) reported that betaine replacement of methionine and choline can significantly reduce serum triglyceride levels in broiler chickens, increase serum phospholipid content, abdominal fat percentage and liver fat were significantly decreased. Feng Jie (1996), Ma Yulong (1998), and Wang Yizhen (1998) found that betaine can significantly reduce the fat content in the liver of animals and significantly reduce the thickness of back carcasses of pigs and the abdominal fat percentage of poultry. Studies have found that betaine can significantly increase the levels of very low-density lipoproteins in layer serum (Ma Yulong, 1998), and promote the synthesis of phospholipids in the body, while phospholipids can reduce the activity of lipogenic enzymes in the liver of mice (Kadir et al., 1995). And triglyceride content. It follows that betaine promotes the synthesis of phospholipids in the body. On the one hand, it reduces the activity of lipogenic enzymes in the liver. On the other hand, it promotes the synthesis of lipoproteins in the liver, of which very low-density lipoproteins are used as carriers. The main apolipoprotein of triglyceride originated, which promoted the fat migration in the liver and reduced the triglyceride content in the liver. Triglyceride accounts for about 99% of animal body fat, which is the main form of energy storage in animals. Its decomposition process is the degradation process of body fat. The decrease in serum triglyceride content indicates that lipolysis is enhanced and direct response is reflected in the decrease in abdominal fat rate. From the above, it can be seen that betaine acts as an anti-fatty liver by lowering body fat by promoting fat breakdown and suppressing fat production. 3.4 Effect of betaine on osmotic pressure regulation and efficacy of anticoccidial drugs Betaine regulates osmotic shock and buffer function. When the body is exposed to stress (such as high temperature, diarrhea, coccidiosis, etc.), the osmotic pressure in the outside world changes, and the cells themselves begin to produce or absorb betaine to maintain the normal osmotic pressure balance, prevent the loss of water and salt The invasion of the species can improve the function of the sodium-potassium pump and help protect the normal function of the gastrointestinal tract, thereby reducing the degree of stress damage, maintaining a good health condition, and reducing the occurrence of death. Hall (1995) reported that feeding the cattle with betaine before and after long-distance transportation can significantly reduce the stress during transportation, and the weight recovery of the cattle is accelerated. Ding Xicheng et al. (1999) found that betaine improved the imbalance of electrolysis in animals caused by E. maxima infection, and significantly inhibited the reproduction of E. maxima schizonts. Peng Xinyu et al. (1999) reported that broiler chickens infected with Eimeria tenella can be used to increase the weight gain of broiler chickens and the anticoccidial index of polyether antibiotics, especially madura In the betaine group, the weight gain was most obvious (the relative weight gain rate was increased by 19%), and the anticoccidial index was increased by 24.7%. It can be seen that betaine is an effective buffer for the osmotic shock of organisms, and can act together with ionophore anticoccidial drugs to protect intestinal mucosal cells, ensure the normal function of cells, and improve the efficacy of anticoccidial drugs. 3.5 Induction of Betaine: Since the 1970s when Finnish scientists discovered that betaine has a special attractant effect on aquatic animals, betaine has been widely recognized and applied as a attractant for aquaculture. Aquaculture Although the artificial bait used in the diet is full-fledged, it is still a boring food for aquatic animals. In addition to sight and touch, the role of smell and taste is particularly important for fish. Some scholars in the United States, Japan, and other countries have studied fish and shrimps, and 0.0001 mol/L of betaine can cause a taste response in all fish. Clarke (1994) reported that betaine in freshwater has no significant effect on the growth and death of salmon, and the feed fed with betaine in seawater has a significant increase in the growth of the fish. Xue Yongrui (1995) showed that the addition of 0.1%, 0.2%, and 0.3% betaine to feed increased the yield by 16.5%, 17.4%, and 21.5%, respectively, compared to the control group. Yan et al. (1994) added betaine 0.3%, crude betaine hydrochloride 0.5% and fine 0.3%, respectively, to carp feed. The weight gain rate increased by 49.23%, 41.78%, and 43.84%, respectively, in the control group. The decrease was 24.16%, 22.13% and 14.13%. Chang Zhizhou et al. (1982) added 1.25% betaine to the crab diet. The net weight gain of crabs increased by 95.3%, and the survival rate increased by 38%. A faster growth rate and a higher survival rate were obtained.