Table 1.

Properties of FPs.

Fluorescent Protein	Excitation/Emission maxima (nm)	Extinction coefficient (M-1 cm-1)	Quantum yield	Relative brightnessa	Maturation half-time (h)	Photobleaching half- time (s)b	pKa
DsRed-Express2c	554/591	35,600	0.42	0.41	0.7	64 ± 4	4.5
E2-Red/Green (green)	484/498	100,200	0.06	0.17	0.4	236 ± 8d	4.0
E2-Red/Green (red)	560/585	53,800	0.67	0.98	1.2	93 ± 3	4.5
E2-Orange	540/561	36,500	0.54	0.54	1.3	81 ± 3	4.5
mOrange2	549/563	56,300	0.49	0.75	4.5	40 ± 3	7.5
KO	548/560	72,800	0.55	1.1	3.8	21 ± 2	5.0
mKO2c	549/563	54,300	0.41	0.54	1.2	9 ± 1	5.0

Unless otherwise indicated, all measurements were carried out during the present study using standardized procedures.

^a Brightness was calculated as the product of extinction coefficient and quantum yield, and was normalized to a value of 1 for wild-type DsRed as calculated from Ref. 5.

^b Photobleaching half-times during widefield illumination are listed as mean ± s.e.m. for three independent replicates.

^c For DsRed-Express2 and mKO2, all data except the pK_a measurements were taken from Ref. 5.

^d The photobleaching half-time for the green chromophore of E2-Red/Green cannot be compared directly to the photobleaching half-times of red chromophores because a different filter set was used.