Characterization of 4‐hydroxyphenylpyruvate dioxygenase

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Abstract
The primary structure of Pseudomonas 4‐hydroxyphenylpyruvate dioxygenase was determined. Sequence degradation of the intact protein and of peptides from three different digests of the carboxymethylated protein established a 357‐residue polypeptide chain with a free α‐amino group. Hydroxylamine cleavage at a single Asn‐Gly sequence was useful. Comparisons with known structures in data banks revealed no close relationship with other characterized proteins. The human enzyme has a related composition, suggesting that also the eukaryotic form belongs to this protein type, but with a blocked N‐terminus like in many other eukaryotic intracellular proteins. Secondary structure predictions suggest an α/β mixed structure, fairly typical of globular proteins, without long segments of hydrophobicity or charge, although a region in the middle of the C‐terminal third of the subunit appears to have the most extreme properties. A ferric centre, correlating with enzyme activity and absorbance at 595 nm, has previously been assigned to tyrosinate coordination. The Tyr and His distributions, and the position of a single Cys residue, all suggest a few likely sites, outside the C‐terminal segment, for this centre.