Characterization of 4-hydroxyphenylpyruvate dioxygenase. Primary structure of the Pseudomonas enzyme

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 alpha-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 alpha/beta 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.

6-hydroxylation: effect on the psychotropic potency of tryptamines

6-Hydroxy-5-methoxy-N,N dimethyltryptamine and 5-methoxy-N, N-dimnethyltryptamine were synthesized and their psychotropic effects compared on trained rats in a Skinner box. The nonhydroxylated form was the more po tent. The metabolism of 5-methoxytryp tophol acetate ester was also studied to determine whether hydroxylation might occur in other than the six position with exogenous indoles. One metabolite was formed, with properties of a hydroxy-5-methoxyindole-3-acetic acid, which proved on chromatography not to be the 6-hydroxy structural isomer. Phar macologic and metabolic studies suggest that psychotropic activity of trypt amines may result from metabolites other than the 6-hydroxylated forms.