histidinin

Histidine is one of the twenty standard amino acids used by living organisms to synthesize proteins. It features an imidazole side chain, which can accept or donate protons near physiological pH, giving histidine buffering capacity and enabling roles in enzyme catalysis and metal ion coordination. The imidazole ring also allows histidine to participate in various interactions within proteins, contributing to active sites and structural stability.

In humans, histidine is considered essential for infants and is often described as conditionally essential for adults, meaning that adequate dietary intake is important for growth and development, with requirements that can vary among individuals. Histidine is widely distributed in protein-rich foods, and regular diets typically provide sufficient amounts. Good sources include meat, fish, poultry, eggs, dairy products, and to a lesser extent certain plant-based foods such as legumes and whole grains.

Metabolic and physiological roles include its incorporation into proteins during synthesis, serving as a precursor to histamine via histidine decarboxylase, and contributing to signaling pathways and immune responses through histamine release. The imidazole side chain also enables histidine to act as a ligand in metalloproteins, aiding in the binding of metal ions such as zinc and iron, which is important for catalytic activity in various enzymes.

Clinical notes include the rare inherited disorder histidinemia, caused by deficiency of histidine ammonia-lyase, which leads to elevated histidine levels in blood and urine but is often asymptomatic. Most individuals obtain adequate histidine through a balanced diet, and supplementation is typically not required unless directed by a medical professional.