Table 1.

Spectral properties and proton‐pumping activity of the AR3 and AR3(F229S) pigments generated in this study

Pigment	Retinal analog	λ max (nm)	Normalized proton‐pumping
			H+ white	H+ 617	H+ 660	H+ 730
AR3 WT	A1	556	+++	++++	+++	−
	A2	578	+++	++++	+++	+
	MOA2	546	+	+	nd	nd
	MMAR	592	++	+++	+++	++++
	14F	583	nd	nd	nd	nd
	All‐E	562	nd	nd	nd	nd
AR3(F229S)	A1	560	++++	++++	++	−
	A2	581	+++	++++	++++	++
	MOA2	537	+	+	nd	nd
	MMAR	580	++	+++	+++	+++

The λ _max was determined from hydroxylamine difference spectra in solubilized membrane vesicles in 2.5% DDM. Accuracy of the λ _max values ±2 nm. The proton‐pumping activity was determined under four illumination conditions. To facilitate comparison, and more clearly show the general trend, all proton‐pumping rates of the pigments are normalized to the highest activity attained within a set of light conditions. For instance, AR3(F229S):A1 displayed the highest activity of 2 H⁺ mol⁻¹ s⁻¹ under white light illumination. Therefore, the proton‐pumping activity under white light illumination for all analog pigments was normalized to 2. The pigments with the highest activity attained for each set are the following: White light – AR3(F229S):A1 (2 H⁺ mol⁻¹ s⁻¹); 617 nm – AR3(F229S):A1 (1.4 H⁺ mol⁻¹ s⁻¹); 660 nm – AR3(F229S):A2 (1 H⁺ mol⁻¹ s⁻¹) and 730 nm – AR3:MMAR (0.3 H⁺ mol⁻¹ s⁻¹). For further details see the corresponding Materials and Methods section. Explanation of symbols: ++++: 100–70% of highest rate under that condition; +++: 70–40%; ++: 40–20%; +: 20–5%; −: <5%. nd = not determined.