In the (*) Ames test, mutagenesis is assayed by looking for revertants of Salmonella typhimurium that originally cannot synthesize this amino acid.
The unusual biosynthesis of this amino acid from purine precursors has been cited as evidence for the RNA World hypothesis. In affinity chromatography, nickel resins can be used to bind proteins containing a tag with 6 or more of this amino acid. In zincÂ­finger motifs, the zinc ion is ligated by two cysteine residues and two of this amino acid. In the (*) Ames test, mutagenesis is assayed by looking for revertants of Salmonella typhimurium that originally cannot synthesize this amino acid. This amino acid has a side chain with a pKa ofaround 6. It is almost always the "base" that directly deprotonates water in the catalytic triad of serine and cysteine proteases. The decarboxylation of this amino acid produces a compound, released in mast cell degranulation, whose receptors are antagonized by Benadryl's active ingredient. For 10 points, name this amino acid with an imidazole side group, closely related to the immune modulator histamine.
The unusual biosynthesis of this amino acid from purine precursors has been cited as evidence for the RNA World hypothesis.
histidine [accept His or H]