Abnormal circulating amino acid concentration Abnormal circulating proteinogenic amino acid concentration An elevated level of a proteinogenic amino acid in the blood circulation. These are the 23 alpha-amino acids that are precursors to proteins, and are incorporated into proteins during translation. The group includes the 20 amino acids encoded by the nuclear genes of eukaryotes together with selenocysteine, pyrrolysine, and N-formylmethionine.