I have no idea whether this information is relevant to muscle building or protein intake but thought that is was interesting enough to share. Even though leucine is a small percentage of muscle tissue it is still key to signaling protein synthesis. It appears that leucine has the ability to bypass usage in the gut and the liver leading to high blood levels. The high blood levels signals the mTor pathway to initiate protein synthesis.
The concentration is in Molar concentration (mM) .
acids in skeletal muscle: Are protein supplements as good as advertised?
Optimal protein intake to maximize muscle protein synthesis - Biolayne
Episode 2 of Muscle College Radio: Muscle Protein Synthesis ...
Amino Acids - structure, advantages, properties, classification