Resonance Raman Studies of Catecholate and Phenolate Complexes of Recombinant Human Tyrosine Hydroxylase

Human tyrosine hydroxylase isoform 1 (hTHl) was expressed in Escherichia coli, purified as the apoenzyme, and reconstituted with iron. The resonance Raman spectra of hTHl complexed with dopamine, noradrenaline, tyramine, and catechol have been studied and compared to those obtained for TH isolated from bovine adrenal glands or rat phaeochromocytoma tissue. A TH-phenolate complex is reported for the first time. Using dopamine selectively ¹⁸O-labeled in the 3-position or both 3- and 4-hydroxy positions, we have been able to assign unambiguously the origin of the low-frequency vibration bands: the band at 631 cm^-1 involves the oxygen in the 4-position; the band at 592 cm^-1 involves the oxygen in the 3-position, and the band around 528 cm^-1is shifted by both, suggesting a chelated mode vibration. A small shift of the 1275 cm^-1 band and no shift of the 1320 cm^-1band were observed, showing that those two bands involve essentially ring vibrations of the catecholate moiety, rather than the C-O stretching vibration as previously suggested. The spectrum of the catechol-d₆hTHl complex confirms this assignment. The resonance Raman spectra of the ⁵⁴Fe, ⁵⁶Fe, or ₅₇Fe isotope-containing enzymes complexed with dopamine are virtually identical, showing that the component of the iron in the ≈600 cm^-1vibrations is too small to be observed. These results provide a better understanding of the Raman properties of iron-catecholate complexes in this enzyme, as well as in other metalloproteins and model compounds.