Imidazole-bearing amino acid with side-chain pKa ≈ 6. Uniquely able to act as both H+ donor and acceptor at physiological pH — central to acid-base catalysis and metal coordination (heme Fe, Zn, Cu).
Imidazole-bearing amino acid with side-chain pKa ≈ 6. Uniquely able to act as both H+ donor and acceptor at physiological pH — central to acid-base catalysis and metal coordination (heme Fe, Zn, Cu).