Histidine Ammonia Lyase (HAL)

Histidine ammonia-lyase (HAL), also known as histidase (EC 4.3.1.3), is a cytosolic enzyme catalyzing the first reaction in histidine catabolism, the nonoxidative deamination of L-histidine to trans-urocanic acid.

The cDNA predicted a 657-amino acid protein with a molecular mass of approximately 72.6 kD. The authors identified at least 2 different transcription sites, for liver and skin, respectively.By restriction mapping and Southern blot analysis of isolated clones, Suchi et al. (1993) showed that the HAL gene spans approximately 25 kb and consists of 21 exons. Exon 1 encodes only the 5-prime untranslated sequence of liver histidase mRNA, with protein coding beginning in exon 2. A rarely observed 5-prime GC, similar to that reported in CYP11A , a human P-450 gene, is present in intron 20.