Fig. 3.
Flash dependence of the protonated water cluster band (from W5+) at 263 K. (A) Positive 2,880-cm−1 cationic water cluster band in the calcium S2-minus-S1 difference spectrum (black), generated by a single flash after dark adaptation, compared with calcium-depleted (gray; repeated from Fig. 2A, gray). (B) Calcium S3-minus-S2 spectrum (black), generated by two actinic flashes after dark adaptation, compared with calcium-depleted (gray; repeated from A, gray). (C) Calcium S0-minus-S3 spectrum (black), generated by three actinic flashes, compared with the calcium-depleted (gray; repeated from A, gray). (D) Calcium S1-minus-S0 spectrum (black), generated by four actinic flashes after dark adaptation, compared with calcium-depleted (gray; repeated from A, gray). The calcium-depleted difference spectrum was acquired with a single flash to a dark-adapted sample and corresponds to S2′-minus-S1. (E) Baseline (S1-minus-S1) acquired from dark-adapted, calcium-depleted PSII. Spectra are averages of 31 (A–D, black) and 15 (A–E, gray) samples. y axis ticks represent 1 × 10−4 absorbance units.