4-Nitrocatechol as a colorimetric probe for non-heme iron dioxygenases.

作者：C.A. Tyson · 发表于：Journal of Biological Chemistry · 年份：1975 · DOI：10.1016/s0021-9258(19)41759-6 · 被引用次数：54 · 研究领域：Enzyme function and inhibition、Electrochemical sensors and biosensors、Hemoglobin structure and function

4-Nitrocatechol is examined as an active site probe for non-heme iron dioxygenases and found to be of value, particularly with those containing iron in the Fe(II) oxidation state. 4-Nitrocatechol is astrong competitive inhibitor of substrate oxygenation by protocatechuate 3,4-dioxygenase, forming a reversible complex with this enzyme, and by pyrocatechase. The number of binding sites per enzyme molecule titrated spectrophotometrically with 4-nitrocatechol agrees with results from previous studies with either the principal substrate or other analogues, as expected of an effective probe. Despite these facts and the observation that both enzymes cleave the same substrates at the same carbon-carbon bond, the optical and electron paramagnetic resonance (EPR) spectra of their 4-nitrocatechol complexes are remarkably different. The 4-nitocatechol-protocatechuate 3,4-dioxygenase optical spectra resemble that of the 4-nitrocatecholate ion shifted 20 to 30 nm to longer wavelength. Concomitant with this change the EPR signal centered at g equal 4.28 shows increased rhombicity (g values at 4.74, 4.28, and 3.74). In contrast, the spectrum of the 4-nitrocatechol-pyrocatechase complex has a maximum at the same wavelength as that of a 1:1 solution of free Fe(II) and 4-nitrocatechol in the absence of enzyme after titration of the catecholic protons with base and the g equal 4.28 EPR signal is not resolved at liquid N-2 temperature. These changes are interpreted as resulting in part from a pro...