Table 1 Characteristics of GFP-like far-red fluorescent proteins.

	eqFP670	E2-Crimson	mNeptune	eqFP650	mCardinal	Katushka	mNeptune2.5	Katushka2S
Excitation peak (nm)	605	605	599	592	604^d	588	599^d	588^b
Emission peak (nm)	670	646	649	650	659^d	635	643^d	633^b
Fluorescence quantum yield	0.06	0.12	0.18	0.24	0.19^d	0.34	0.28^d	0.44^b
Molar extinction coefficient (М^−1·cm⁻¹) at excitation maximum	70,000	58,500	57,500	65,000	87,000^d	65,000^b	95,000^d	67,000^b
Brightness (a.u.)^a	4,200	7,080	10,350	15,600	16,530^d	22,100	26,600^d	29,480^b
Maturation half-time (min)^c	ND	ND	18^b	18^b	27^d	25^b	26^d	14^b
Photostability, widefield (s)	1420^b	46^b	500^b	404^b	ND	208^b	ND	72^b
pKa	4.5	4.5	5.8	5.7	5.8^d	5.5	5.3^d	5.4^b
References	⁴	³	²	⁴	⁶	¹	⁶	this work

^aproduct of fluorescence quantum yield and molar extinction coefficient.
^bmeasured in this work. Katushka2S fluorescence quantum yield was determined relative to Katushka.
^ceqFP670 and E2-Crimson do not mature in vitro in our assay.
^ddata from Ref. 6.

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