This domain is one of two barrel-shaped regions that together form the active enzyme, 4-hydroxyphenylpyruvic acid dioxygenase, EC:1.13.11.27. As can be deduced from the disposition of the various Glyoxalase families, _2, _3 and _4 in Pfam, pfam00903, pfam12681, pfam13468, pfam13669, these two regions are similar to be indicative of a gene-duplication event. At the individual sequence level slight differences in conformation have given rise to slightly different functions. Pseudomonas hpd encodes a 4-hydroxyphenylpyruvic acid dioxygenase catalyzes the formation of homogentisate from 4-hydroxyphenylpyruvate, and the pyruvate part of the HPPD substrate (4-hydroxyphenylpyruvate), derived from L-tyrosine, and the O2 molecule occupy the three free coordination sites of the catalytic iron atom in the C-terminal domain. In plants and photosynthetic bacteria, the tyrosine degradation pathway is crucial because homogentisate, a tyrosine degradation product, is a precursor for the biosynthesis of photosynthetic pigments, such as quinones or tocopherols.
Jiyao W et al.(2023). "The conserved domain database in 2023.",