Table 2.

Summary of all-trans retinol binding parameters to IRBP. The binding of all-trans retinol to full-length IRBP and the four modules was determined by measuring the enhancement of all-trans retinol fluorescence and the quenching of protein endogenous fluorescence as a function of retinol concentration.

Protein	Binding sites (N) Kd (μM)	Enhancementa	Quenchingb
Full-length IRBP	N =	3.19 ± 0.10	1.93 ± 0.41
	Kd =	0.30 ± 0.05	0.66 ± 0.14
Module 1	N =	0.83 ± 0.15	0.25 ± 0.10
	Kd =	0.44 ± 0.13	0.35 ± 0.08
Module 2c	N =	1.57 ± 0.04	1.31 ± 0.06
	Kd =	0.084 ± 0.022	0.14 ± 0.04
Module 3	N =	1.83 ± 0.42	0.65 ± 0.08
	Kd =	1.18 ± 0.41	0.31 ± 0.04
Module 4	N =	2.06 ± 0.53	0.12 ± 0.05
	Kd =	1.79 ± 0.54	0.64 ± 0.05

^a Monitored at 480 nm upon excitation at 330 nm.

^b Monitored at 340 nm upon excitation at 280 nm.

^c Module 2 data from Loew et al. Exp Eye Res. 2001, 73:257–264