. 2016 May;13(118):20160133. doi: 10.1098/rsif.2016.0133

Table 1.

Comparison of spectroscopic features of different semiquinones reported for the Q_o site. n.s., data not shown in the paper or experiment not performed; n.a., not applicable; SQ_o, semiquinone in the Q_o site; SQ_i, semiquinone in the Q_i site; SQ_res, stigmatellin-insensitive radical signal.

properties of the signal/signals		SQ_o reported by
		de Vries et al. [31]	Zhang et al. [33]	Cape et al. [34]	Vennam et al. [35]	Sarewicz et al. [36]
		de Vries et al. [31]	Zhang et al. [33]	Cape et al. [34]	Vennam et al. [35]	SQ_o uncoupled	SQ_o–FeS spin-coupled
transience of signal		n.s.	yes	n.s.	n.s.	yes	yes
sensitivity to specific Q_o-site inhibitors:	stigmatellin	n.s.	yes	yes	yes	yes	yes
	myxothiazol	n.s.	no	n.s.	n.s.	yes	yes
	strobilurins	n.s.	n.s.	n.s.	n.s.	yes	yes
presence of stigmatellin-insensitive residual signal		n.a.	n.a.	yes	yes	no	no
g-factor of central line		2.005	2.0040	2.0054	2.0044^a	2.005	1.94
linewidth of X-band spectrum of SQ_o [G]		8.3	11.7	11.9	11.6	14.2	n.a.
microwave power saturation		saturable; slower relaxation than SQ_i	saturable at 130 K; similar to SQ_i	saturable at 77 K; similar to SQ_res	n.s.	non-saturable at 200 K	n.s.
temperature-dependence of the EPR spectrum amplitude		n.s.	n.s.	n.s.	n.s.	anti-Curie behaviour	n.s.
spin–spin exchange interactions		no	no	no	no	no	yes
dipole–dipole interactions with:	reduced FeS	no	no	no	no	possibly yes	n.a.
dipole–dipole interactions with:	oxidized haem b_L, c₁	no	no	no	yes	yes	yes^b
interaction with magnetic nuclei	hydrogen	n.s.	n.s.	deprotonated	deprotonated	n.s.	n.s.
interaction with magnetic nuclei	nitrogen	n.s.	n.s.	no	no	n.s.	n.s.

^aReported for yeast cytochrome bc₁.

^bInteraction between SQ_o–FeS coupled centre and oxidized haem b_L is inferred from pulse EPR measurements [37].