Histidine ammonia-lyase

Histidine ammonia-lyase (HAL), also known as histidase, is an enzyme that catalyzes the deamination of histidine to urocanic acid and ammonia. This enzyme plays a crucial role in the metabolism of histidine, an essential amino acid in many organisms.

Structure

Histidine ammonia-lyase is a tetramer composed of identical subunits. Each subunit contains a pyridoxal phosphate (PLP) cofactor, which is essential for the enzyme's catalytic activity. The enzyme's structure is characterized by a large, central, eight-stranded beta-sheet surrounded by alpha-helices.

Function

Histidine ammonia-lyase is primarily involved in the catabolism of histidine. It catalyzes the first step in this process, converting histidine to urocanic acid and ammonia. This reaction is a key part of the histidine degradation pathway, which allows organisms to use histidine as a source of energy and to recycle its components for other purposes.

Clinical significance

Mutations in the gene encoding histidine ammonia-lyase can lead to a rare metabolic disorder known as histidinemia. This condition is characterized by elevated levels of histidine and histamine in the blood and urine, and can cause a variety of symptoms including intellectual disability, speech impairment, and growth retardation.

See also

• Histidinemia
• Histidine metabolism
• Urocanic acid
• Ammonia