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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.

From: Module structure of interphotoreceptor retinoid-binding protein (IRBP) may provide bases for its complex role in the visual cycle – structure/function study of Xenopus IRBP

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
  1. aMonitored at 440 nm upon excitation at 360 nm.
  2. bMonitored at 340 nm upon excitation at 280 nm.
  3. cModule 2 data from Loew et al. Exp Eye Res. 2001, 73:257–264.