Isoleucine estimated requirements

From the viewpoint of required energy, the biosynthetic process is extravagant indeed, yet protein machines can be remarkably efficient in spite of diverse function. For example the efficiency of the F]-ATPase in rotating an actin filament has been estimated to approach 100%. Why are these twenty amino acid residues required and why, for example, are leucine and valine residues functionally different from an isoleucine residue Such questions raise the issue as to whether there might be a common groundwork with which to understand protein function using these twenty amino acid... 

Thus, the term 60 W estimates the maintenance requirement for available lysine. Similar equations are available for the other indispensable amino acids for which the requirements of layers have been quantified in addition to lysine, these include methionine (often the first-limiting amino acid for layers), tryptophan and isoleucine. Glycine (or its substitute, serine) is apparently non-essential for layers. 

Reducing the level of dietary crude protein (CP) is an effective means to reduce nitrogen excretion but requires reliable information about the pigs requirements for potentially limiting amino acids (AA). Isoleucine (lie) may be limiting in low CP pig diets that are supplemented with lysine (Lys), threonine, methionine and tryptophan (Liu et al., 1999). The objective of this study was to estimate the optimum dietary standardized ileal digestible (SID) Ile Lys ratio in 25- to 40-kg pigs that were fed wheat-barley based diets. 

Isoleucine has often been considered to be among the next-limiting amino acids for growth in pigs, after Lys, Met, Met+Cys, Thr and Trp. However, there are conflicting reports concerning the requirement for He. Differences in requirement estimates may be due to differences in experimental conditions. The initial two steps of the catabohsm of the branched-chain amino acids (BCAA i.e. He, Val, and Leu) are catalyzed by enzyme-complexes shared by the three BCAA. An excessive supply of one BCAA may therefore stimulate the catabolism of the other BCAA. The objective of this study is to perform a meta-analysis of hterature data and to identify the sources of variation in the reported He requirement. 

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