Table 4.

Summary of 9-AS binding parameters to Xenopus IRBP as determined by fluorescence spectroscopy. The binding of 9-AS to full-length IRBP and the four modules was determined by measuring the enhancement of 9-AS fluorescence and the quenching of protein endogenous fluorescence as a function of 9-AS concentration.

Protein	Binding sites (N) Kd (μM)	Enhancementa	Quenchingb
Full-length IRBP	N =	2.58 ± 0.17	0.18 ± 0.29
	Kd =	0.28 ± 0.07	0.29 ± 0.11
Module 1	N =	2.55 ± 0.24	0.97 ± 0.19
	Kd =	0.33 ± 0.15	0.42 ± 0.10
Module 2c	N =	1.49 ± 0.15	0.93 ± 0.06
	Kd =	0.25 ± 0.08	0.13 ± 0.02
Module 3	N =	2.76 ± 0.09	1.06 ± 0.07
	Kd =	0.16 ± 0.41	0.19 ± 0.03
Module 4	N =	2.23 ± 0.09	0.30 ± 0.09
	Kd =	0.082 ± 0.037	0.16 ± 0.04

^a Monitored at 440 nm upon excitation at 360 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.