| Systems for sensing specific sugars, such as galactose or maltose, or specific amino acids, such as histidine or proline, also are present. |
| The mixture was later solidified by means of a surface agar solution containing traces of histidine and biotin. |
| Starvation for histidine derepresses the entire operon, the longest then known. |
| In addition to histidine and biotin, the top agar contained minimal tryptophan to support E.coli growth. |
| The essential amino acids are histidine, tryptophan, threonine, valine, phenylalanine, leucine, methionine, lysine, and isoleusine. |
| Urocanic acid, imidazole propenoic acid, is a metabolic product of histidine, which accumulates in skin and is excreted in sweat. |
