Table 1.

Hydroxyl radical modification rate constants for residues in rhodopsin

PeptideRhodopsin (s−1)Meta II (s−1)Opsin (s−1)Ratios of rate constants
Meta II/ rhodopsinMeta II/opsinOpsin/rhodopsin
85FM*VFGGF917.4 ± 0.2§22.6 ± 1.42.1 ± 0.4310.80.3
113EGFF*116238.1 ± 21370 ± 16.5254 ± 471.61.51
140C*KPM*SNF1464.2 ± 0.58.0 ± 0.616.2 ± 0.9††1.90.53.8
147RFGENHAI*M*G1563.8 ± 0.46.6 ± 0.4ND‡‡1.7
160TWVM*A1644.5 ± 0.513.6 ± 1.412.8 ± 1.5312.8
176SRYIPEGM*Q1841.8 ± 0.81.1 ± 0.51 ± 0.111.10.6
288M*TIPAF2934.2 ± 0.37.6 ± 0.56.6 ± 0.41.81.21.6
293FAKTSAVY*NP*VIY*3062.1 ± 0.51.1 ± 0.24.0 ± 1.10.50.32
333ASTTVSKTETSQV*A*P*A*3488.1 ± 0.37.9 ± 0.46.8 ± 0.3110.8
  • *, Denotes residue(s) modified by hydroxyl radicals.

  • Rate constants were estimated by employing a nonlinear fit of hydroxyl modification data to a pseudo first order decay as described in Materials and Methods (supplement).

  • Peptides detected following LC-MS analysis and confirmed by MS/MS analysis with rate constants of modification suitable for quantitative analysis. As shown in Figure 1, other peptides exhibited modifications that were confirmed by tandem MS/MS.

  • §Error in rate constant estimation calculated from nonlinear fit.

  • Rate constants reflect mixed modifications.

  • ††Rate determined from peptide 137–146 with the same modified residues as peptide 140–146.

  • ‡‡Peptide not detected in this experiment, no rate is reported.