Plasma and tissue-free amino acids in the developing chick.

The free amino acids of the plasma and pectoral muscle, liver and brain cytosolic S105 supernatant obtained from 2- and 3-week-old fasted chicks, were analyzed by HPLC after deproteinization by ultrafiltration. Protein-bound amino acids were analyzed in parallel studies. A clear relationship between the free and bound tissue amino acids was apparent. Only for the gluconeogenic amino acids a close correlation was evident between the plasma and the muscle free amino acids. A relatively steady composition of the free amino acids is established early in the tissues, but in the plasma it changes significantly with age.