Table 1.

Peak wavelengths and pKa values

Protein15Z peak, nm15Z pKa15E peak, nm15E pKa
SyCcaS5385.8 ± 0.16728.6 ± 0.2, —
RcaE5315.6 ± 0.16627.9 ± 0.2, 8.9 ± 0.5
RcaE*6626.4 ± 0.25986.1 ± 0.2
NpR6012g46626.0 ± 0.35985.8 ± 0.2
RcaE Y227F5335.6 ± 0.16637.8 ± 0.1, 8.6 ± 0.5
RcaE H285Q5335.7 ± 0.16637.2 ± 0.2
RcaE Y187F5335.5 ± 0.16706.9 ± 0.1, 9.4 ± 0.3
RcaE L249H6327.5 ± 0.25666.4 ± 0.2, 10.1 ± 0.4
RcaE F252H5355.2 ± 0.36267.1 ± 0.6
RcaE E217D5375.5 ± 0.26408.1 ± 0.2, 9.1 ± 0.2
RcaE E217A5335.5 ± 0.5540—, 9.8 ± 0.4
RcaE E217Q5335.7 ± 0.6540—, 10.0 ± 0.2
RcaE K261M5335335.8 ± 0.7, 6.9 ± 0.8
RcaE K261A5275275.3 ± 0.6, —
  • To derive pKa values, absorption data at at least five wavelengths were fit as a function of pH to models for one or two titrating groups as described in SI Data Analysis. Errors are reported as SDs about the mean for the fitted values. Cases in which a transition was not seen are indicated with a dash. Values were measured under native conditions unless otherwise stated, with native peak wavelengths reported for pH 7.5.

  • *RcaE also was examined under denaturing conditions to measure the pKa of the covalent PCB adduct in the absence of native protein structure. Peak wavelengths are reported at pH 2.0.

  • The red/green CBCR NpR6012g4, belonging to a different subfamily, also was examined under denaturing conditions to provide an independent measurement. Peak wavelengths are reported at pH 2.0.