Interaction of spin-labeled tryptamine with monoamine oxidase: probing the microenvironment of the active site by spin probe-spin label techniques

Observation of a Flavin Semiquinone in the Resting State of Monoamine Oxidase B by Electron Paramagnetic Resonance and Electron Nuclear Double Resonance Spectroscopy,

“…A flavin semiquinone would be expected to give rise to a radical EPR signal. X-Band EPR studies employing spinlabeled substrates and inactivators of the enzyme (Buckman & Eiduson, 1980;Zeidan et al, 1980;Zeidan, 1988), radical traps of turnover products (Yelekci et al, 1989), and partially reduced enzyme (Igaue et al, 1967;Yue et al, 1993) have been reported. An EPR signal from the resting state enzyme has not yet been reported, however.…”