... histidine is also basic. Other common groupings are the aliphatic or neutral amino acids (glycine, alanine, isoleucine, leucine, valine, serine, threonine and proline). Proline differs in that ... organs in the body, but amino acids are consumed in the diet from a variety of protein sources. In addition, each amino acid is maintained in part as a free amino acid in solution in blood and inside ... historically in the opening chapter and considered in separate chapters on individual essential nutrients and in those on taurine, homocysteine, glutamine, arginine, choline, and carnitine.There...