SUPPLEMENTARY INFORMATION
Clausen & Junge 2004
On the contributions of YZ (very small!) and of Mn4Ca to
absorption transients around a wavelength of 360 nm.
Oxidized minus reduced difference spectra of tyrosine (YZ) in PSII core particles, the
contribution of tyrosine to a wavelength of 360 nm is very small.
Corrected difference spectra of YZox – YZ in oxygen-evolving PSII core particles at pH 5.5 (solid
line) and in Mn-depleted centres at pH 9 (dotted line) and pH 5.7 (dashed line) in the UV, blue,
green and red spectral regions.

Data from: Haumann,M., Mulkidjanian,A. & Junge,W.
Tyrosine-Z in oxygen evolving photosystem II: a hydrogen-bonded tyrosinate.
Biochemistry 38, 1258-1267 (1999).

Data from: J. P. Dekker, H. J. van Gorkom, M. Brok & L. Ouwehand
Optical characterization of photosystem II electron donors.
Biochim. Biophys. Acta 764 (1984) 301-309.
Data from: W. Weiss & G. Renger

Studies on the nature of the water-oxidizing enzyme. II. On the functional connection
between the reaction-center complex and the water-oxidizing system Y in Photosystem II.
Biochim. Biophys. Acta 850 (1986) 173-183.
Oxidized minus reduced difference spectra of the catalytic centre of water oxidation:
the transitions S1S2 and S2S3 produce about equal jumps and S0S1 almost nothing at
a wavelength of 360 nm (arrows).
Difference spectra of the S-state transitions. The arrows indicate a wavelength of 360 nm.

Lavergne,J.
Improved UV-visible spectra of the S-transitions in the photosynthetic
oxygen-evolving system.
Biochim. Biophys. Acta 1060, 175-188 (1991).
On the variation of the pattern of absorption transients at a
wavelength of 360 nm between two preparations of PSII core
particles.
Change of absorption at 360 nm
3
(-I/I*10 )
Totally dark adapted PSII core particles were excited with a train of five laser flashes at ambient
oxygen pressure. The magnitude of the rise upon the first flash of light varies considerably between
different batches even if prepared by the same protocol. The variance reflects different proportions in
different preparations of reaction centres which are incompetent in oxygen evolution. The extent and
the rate of the “undershoot” upon the third flash (indicative of the oxygen producing transition) are
similar. Broadly speaking, the differences of the response to the first flash of light are insignificant
for the analysis of water oxidation.
3
2
1
Air, 1 bar
Air, 1 bar
0
0
200
Time [ms]
400
Controls for the reversibility of the effects which are induced
by high oxygen pressure
FIG. A: This figure is related to the control trace (black) in Fig. 3 of the Letter to NATURE. The
data were obtained with another batch of PSII core particles. The black transient represents the
negative directed signal attributable to S3S0 from a sample which was kept under ambient
oxygen pressure throughout. The red transient was recorded with a sample which was first
exposed to high oxygen pressure (20 min), and thereafter decompressed to ambient oxygen
pressure. Both transients were obtained with samples that were totally dark adapted.
The coincidence of both traces within noise limits proves the reversibility of the effects which are
induced by exposure to high oxygen pressure.
Corrected transients at 360 nm
3
-I/I*10
Control for reversibility: A
Clausen & Junge (for details see Fig. 3 of the manuscript)
Third Flash
Air, 1 bar - sample reequilibrated
after 20 min exposure to 20 bar O2
Air, 1 bar - control
0.0
-0.3
-0.6
0.000
0.025
Time [s]
0.050
0.075
Change of absorption at 360 nm
3
(-I/I*10 )
FIG. B: This figure is related to the control trace (black) in Fig. 1 of the Letter . The black trace
was obtained with a sample kept under ambient oxygen pressure, throughout. The red pattern was
obtained with a sample which was first exposed to high oxygen pressure (20 min), and thereafter
decompressed to ambient oxygen pressure. Both transients were obtained with samples that were
repetitively dark adapted with dark intervals of 2 min duration between groups of five laser
flashes. Although less pronounced than in totally dark adapted samples (see Figs. 1-4, A) the
“undershoot” upon the third flash and the positive jumps upon the first, second and the fifth flash
are evident. Deviations upon the first flash were discussed both in the Letter and further up in the
Supplemental Material.
These features corroborate the reversibility of the effects which are induced by exposure to high
oxygen pressure.
Control for reversibility: B
Clausen & Junge (for details see Fig. 1 of the manuscript)
2.7
#1
#2
#3
#4
#5
1.8
0.9
Air, 1 bar - sample reequilibrated
after 20 min exposure to 20 bar O2
Air, 1 bar - control
0.0
0.0
0.2
Time [ms]
0.4