Histidine Products | Cleanchem - Histidine is an amino acid that plays a key role in the synthesis of proteins and the formation of histamine, a molecule involved in immune responses and regulation of stomach acid. Histidine is a precursor to histamine, which is important for immune function, gastric acid secretion, and as a neurotransmitter in the brain. It is essential in the diet and is important for the growth and repair of tissues, as well as for maintaining proper pH balance in body fluids.