Tryptophan is an essential amino acid need to be obtained from diet in humans. Tryptophan is an essential amino acid and salvaged from host in apicomplexans. The Cryptosporidium species such as C. parvum and C. hominis have the ability to synthesise tryptophan from serine and indole . The gene coding the ortholog of beta subunit of tryptophan synthase was identified in C. parvum and C. hominis genomes, but not in C. muris genome. This suggests that this capability is absent in C. muris. This difference is attributable to the differences in ecological niches of these organisms, epithelial cells of small intestine for C. parvum and C. hominis and gastric glands of stomach for C. muris. The substrates of this reaction, indole and serine are salvaged from host. The metabolism of tryptophan by intestinal bacteria provides indole for C. parvum and C. hominis. The lack of availability of indole for C. muris in stomach may have led to the absence of this capability.
|Enzyme||EC Number||Gene id|
|Tryptophan synthase beta subunit||188.8.131.52||Chro.50503|