Effects of OP and FAA on protein metabolism in tissues

Compared with FAA, the characteristics of OP in animal protein nutrition are not only in absorption, but also in protein metabolism.

Protein deposition is the result of the balance between protein synthesis rate and degradation rate. Due to different tissues, muscle protein deposition is similar to body protein deposition. The effect of synthesis rate on protein deposition is more important than degradation rate. The increase of nitrogen deposition means the increase of synthesis rate;

On the contrary, the degradation rate of liver is more important for protein deposition. In addition, protein deposition is still affected by many factors, such as AA level and some special AA. In addition, the supply form of AA is also an important factor. When SP was used as nitrogen source, the protein deposition of animal body was higher than that of FAA diet or intact protein diet (Hara et al., 1984; pulllain et al., 1989; pulllain et al., 1991);

Zaloga et al., 1991; infante et al., 1992; mnnchi et al., 1993; Boza et al., l995). Compared with the corresponding FAA diet group, the synthesis rate of body protein in peptide fed mice was 26% (funabiki et al., 1990);

The body protein synthesis rate of the chicks infused with casein hydrolysate mainly composed of SP was significantly higher than that of the corresponding FAA mixture group (Le Guowei et al., 1996); the meat yield and lean meat rate of the fattening pigs fed with synthetic oligopeptide increased (Rerat et al., 1988); the egg yield, egg yield and feed conversion rate of the chicks fed with macromolecular casein hydrolysate increased significantly (Shi Yonghui et al ，1996）。

Nielsen et al. (1994) found that under the same AA equilibrium state, hydrolyzed casein, intact casein and Hydrolyzed Soybean protein diet had different effects on the synthesis and degradation of whole protein in rats. The first two improved both protein synthesis and protein degradation, while the latter only inhibited degradation;

At the same time, it was found that the three protein diets had similar effects on the secretion of insulin, insulin-like growth factor and glucagon, and also increased the level of EAA and neaa in plasma. It is suggested that there may be different mechanisms of action between peptides and FAA on protein deposition.

The rapid absorption of SP and the endocrine changes caused by it may be one of the reasons for the changes of protein metabolism in different tissues. Oddy et al. (1986) and boisclair et al. (1993) found that there was a strong correlation between the synthesis rate of muscle protein and the difference of AA content in arteriovenous. The larger the difference of AA content in arteriovenous, the higher the protein synthesis rate.

The affinity of intestinal peptide carriers to peptides containing hydrophobic and side chain larger AA, such as those containing branched AA, methionine and phenylalanine, is high (Matthews, 1991), and these AA also participate in the regulation of tissue protein synthesis and degradation. For example, leucine can promote the synthesis of muscle protein in rats under different physiological and nutritional conditions (rannels et al., 1974; buse et al., 1975; fulks et al., 1975;

Chua et al., 1979; Garrick et al., 1988; funabiki et al., 1992). The rapid increase of plasma AA concentration may increase the plasma insulin concentration (Rerat et al., 1988; Monchi et al., 1993). Garrick et al. (1988) reported the effect of balanced AA on protein synthesis, which can also be repeated by the mixture of essential AA or branched AA. Branched AA can improve the sensitivity of muscle protein to insulin.

Funabiki et al. (1992) thought that leucine, arginine and methionine might be the prolactin of insulin; mcnurlan et al. (1982) found that after leucine was given to rats, insulin in vivo increased rapidly; in particular, the rapid absorption of leucine by animals infused with oligopeptide made the plasma insulin concentration higher than that of animals given FAA (Rerat et al., 1988), while insulin was involved in the prolongation of peptide chain in protein synthesis It may also affect the speed of peptide chain extension and increase protein synthesis in muscle (fundabiki et al., 1992).

The intake of branched chain AA can improve the balance of plasma AA, which may also be the reason of improving protein anabolism. In addition, methionine also plays an important role in protein synthesis. It is the starting AA for the synthesis of all proteins in animals (Waterlow et al., 1978). Yokogoshi et al. (1979) and Muramatsu et al. (1986) found that adding methionine to nitrogen-free diet can increase the number of chromosomes, improve the speed of protein synthesis in liver and whole body, and increase the absolute amount of protein synthesis;

When methionine and cysteine are deficient, due to the rapid oxidation of methionine itself, the utilization of methionine is reduced, and the protein synthesis of unit RNA in chickens and laying hens is reduced, and the synthesis speed is reduced (Kino et al., 1987; hirmoto et al., 1990). Another AA affecting protein synthesis is tryptophan. Lin et al. (1988) found that the incorporation of phenylalanine into the longissimus dorsi muscle increased with the increase of dietary tryptophan concentration. Tryptophan is not only the raw material for protein synthesis, but also may be involved in the regulation of protein synthesis.

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