After the perfusion of tyrosine and FAA or SP, there was a high concentration of AA in the circulation, indicating that in the absorption process, the intestinal tract would first use part of FAA to synthesize peptides, and then transport them into the circulation completely. The significance of this process is not clear at present;

From the characteristics of high solubility, strong stability and low ionic strength of peptides, and the advantages of peptides in alleviating the toxicity of some AA (such as tyrosine and phenylalanine) at high concentrations, this transformation may be of great significance to animals. Protease and enteropeptidase in intestinal cavity and cells only catalyze the hydrolysis of peptide bond. Under certain conditions, FAA may also be used as a substrate for peptide synthesis as in vitro enzyme catalysis (Gaertner and puigserverl988; monter et al., 1991);

This process may be the reason for the high energy consumption of FAA transport and the high peptidase activity of intestinal tissue in FAA diet (Rose et al., 1953). It was found that the γ - glutamic acid cycle is responsible for the transport of tyrosine into tissues, and the transpeptidase combined with the membrane catalyzes the reaction of tyrosine and glutathione to generate γ - glutamyl AA. These two peptides can be absorbed into cells (Meister, 1988), and then hydrolyzed to generate tyrosine and pyroglutamic acid. The latter is further hydrolyzed to generate glutamic acid and glutathione.

γ - glutamyltranspeptidase has a wide range of selectivity for substrates, which can catalyze the formation of other glutamyldipeptides such as γ - glutamyl-l-aa (Meister, 1977). The mechanism and significance of peptide synthesis need further study.

Another source of circulating peptides may be AA metabolism in the liver (backwell, 1994).The peptides in the circulation of hungry animals may mainly come from the release of peptides and the re absorption of endogenous proteins by intestine during the degradation of proteins in gut, liver and spleen. However, it is not easy to observe the intermediate degradation products of proteins in animal tissues, mainly because the proteins in cells will be rapidly degraded to FAA under the action of peptidase (Kito et al., 1989;

Takahashi et al., 1987), and SP can be directly used by tissues (backwall, 1994); Kito et al. (1989) and Takahashi et al. (1987) think that if there are factors that inhibit peptidase activity, the accumulation of peptides in tissues can be observed. Noguchi et al. (198l, 19821988) found an acid soluble peptide which can be excreted with urine and contains trimethylhistidine in muscle tissue.

Le Guowei (1996) found that there were five typical peptide peaks in the plasma of hepatic portal vein when the chicken was in starvation state, and the peptide peaks decreased or decreased significantly after perfusion of op or FAA, which indicated that the degradation and metabolism of chicken tissues had changed under the two states. In addition, it was found that the degradation of protein in liver (grihde, 1984; Hopgood et al., 1977; sommercorn et al., 1981; Mortimore et al., 1987) and muscle (Li et al., 1978; Chua et al., 1978; meieman et al., 1988) decreased after providing nitrogen source or some AA for animal body.

Intestinal reabsorption of endogenous proteins is also one of the sources of circulating peptides. For example, Rerat (1988) found that the total absorption of AA exceeded the perfusion amount after the perfusion of peptide; in rats and pigs, it was also observed that OP had a greater effect on the endogenous protein secretion, while the effect of nitrogen-free diet and FAA was relatively small, and the endogenous protein secretion increased when peptide existed (moughan et al., 1990; butts et al., 1993).

At present, many studies have found that SP can be quickly removed from the blood. For example, SP of glycine-l-glycine dipeptides injected intravenously to mice disappeared rapidly from the blood and could not be detected in urine, muscle, liver, small intestinal mucosa and renal cortex; however, the concentration of AA in blood, muscle, liver and kidney increased.

The presence of AA in blood may be due to the hydrolysis of SP in tissue and its release into cell fluid, because of the high activity of hydrolase in tissue (Boza, 1995). However, SP hydrolase activity in the blood is very small or no activity. When a large amount of l-alanine-l-glutamic acid and glutamic acid-l-tyrosine are injected into human vein, SP is removed very quickly. At the same time, the concentration of AA is increased at the same speed, and a small but relatively stable SP appears in the blood.

Molecular structure is an important factor to determine the disappearance rate of SP from blood. When several kinds of SP were injected intravenously to mice, the speed of SP in blood was different in different AA composition (brandsch et al., 1994). SP with glycine at the end of nitrogen had stronger resistance to hydrolysis. For example, it was found that the hydrolysis rate of glycine-l-leucine in rat's systemic circulation was half of that of alanine-l-cystine.

Shengnuo bio PRODUCT

Best sales manager contact

About Shengnuo

Chengdu Shengnuo Biotechnology Co., Ltd. has "Chengdu polypeptide drug engineering technology research center" in Chengdu, mainly engaged in polypeptide, polypeptide drug and beauty peptide research. Our zero defect has passed the FDA certification, and now it has become the first-class professional peptide drug and product development, technology transfer, technical service and peptide drug industry in the scale production and export of China's parks.