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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.

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 = 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
  1. aMonitored at 480 nm upon excitation at 330 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