Amino acid imbalance-biochemical mechanism and nutritional aspects.

摘要

Amino acid imbalances occur when a second-limiting amino acid or mixture of amino acids lack a particular amino acid is supplemented in diet. In spite of the variation in the conditions that have been used to induce amino acid imbalances, such as protein level in the diet, the extent of differences in total nitrogen content between basal and imbalanced diets, and kinds of amino acids used as imbalancing agents, the conspicuous common features of amino acid imbalances is the decrease concentration of limiting amino acid in blood, decrease in feed intake and weight gain, and increase dietary content of the limiting amino acid needed to correct the imbalances. There is a strong evidence that a decrease in the concentration of a limiting amino acid detected in the anterior prepyriform cortex of the brain is followed by behavioural effects, especially a decrease in feed intake. This might be due to the competition between the limiting amino acid and the amino acids in the imbalanced mixture for transport from the blood to the brain. One of the biochemical responses of animals fed with amino acid imbalanced diet is a rapid decrease in the concentration of the limiting amino acid which is due in part to the increase in catabolism of the limiting amino acid by the increased activities of enzymes involved in the catabolism of the amino acid. Practically, specific amino acid imbalances could be induced in pig and poultry diets that have been supplemented with lysine, methionine, tryptophan when threonine, isoleucine, valine, etc. are potentially third- or fourth-limiting in the diets. In these cases, the supplementation of the limiting amino acid can be beneficial in preventing the decrease in feed intake that can otherwise occur as a result of amino acid imbalance..