| Abstract
| - The interaction of CrII with taurine/α-ketoglutarate (αKG) dioxygenase (TauD) was examined. CrII replaces FeIIand binds stoichiometrically with αKG to the FeII/αKG binding site of the protein, with additional CrII used togenerate a chromophore attributed to a CrIII−semiquinone in a small percentage of the sample. Formation of thelatter oxygen-sensitive species requires the dihydroxyphenylalanine (DOPA) quinone form of Tyr-73. This preformedside chain is generated by intracellular self-hydroxylation of Tyr-73 to form DOPA, which is subsequently oxidizedto the quinone. No chromophore is generated when using NaBH4-treated sample, protein isolated from anaerobicallygrown cells, inactive TauD variants that are incapable of self-hydroxylation, or the Y73F active mutant of TauD. ACrIII−DOPA semiquinone also was observed in the herbicide hydroxylase SdpA.
- A minor portion of TauD with DOPA quinone replacing Tyr-73 is proposed to react with CrII to generate a chromophoric CrIII−semiquinone that reacts with oxygen to form the CrIII−catechol.
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