Table II. Quantification of proteins and Chl labeling in individual PSI and PSII complexes

The same Synechocystis cell culture acclimated to HL2 was labeled separately by [35S]Met/Cys mixture or by [14C]ALA for 30 min and isolated cell membranes separated as a dilution series by CN-PAGE (see Figs. 4 and 7; Supplemental Fig. S6). After exposure of gels in a phosphor imager, bands of individual complexes were quantified using ImageQuant TL 7.0 software (GE Healthcare).

ComplexProtein Labeling: [35S]Met+CysChl Labeling: [14C]ALA
Protein LabelingaNormalized LabelingbNormalized LabelingcMeasured Chl LabelingaMeasured Chl LabelingExpected Chl LabelingdMeasured/Expected
PSI trimer0.36 × 1060.21 × 1062.129.44 × 10658.89.36.31
PSI monomer1.46 × 1062.57 × 10626.35.92 × 10617.538.40.46
PSII dimer2.15 × 1061.86 × 10619.08.76 ×10611.821.90.54
PSII monomer2.98 × 1065.78 × 10652.65.98 × 10611.930.40.39
  • a Absolute values of protein and Chl labeling in PSI and PSII complexes obtained using ImageQuant software and a calibration curve for each complex (Supplemental Fig. S6).

  • b [35S] labeling normalized to a total number of Met and Cys in D1, D2, CP43, and CP47 core proteins for PSII complexes and PsaA and PsaB core proteins for PSI. Although synthesis rates of individual PSII core proteins are different (see Fig. 5), all four proteins contain a similar number of Met and Cys and then their different syntheses can be neglected.

  • c Actual synthesis of PSI/PSII complexes expressed in relative values.

  • d Expected Chl labeling simulates a situation when labeled Chls are evenly distributed to individual complexes synthesized in rates determined by [35S] labeling. Calculation is based on known number of Chl molecules bound to each complex (see text).