Photochemical Reactions of Photosystem II in Ethylene Glycol

Abstract

The behavior of photosystem II (PSII) reactions was investigated under conditions of decreasing water content by the addition of increasing concentrations of ethylene glycol (EG). The photosynthetic activities were measured for PSII samples either directly in aqueous solutions of EG or in the standard buffer medium following EG treatment. Several effects on PSII arise upon exposure to EG. Below 50% EG there are no significant irreversible changes, although there is a slowing of the QA-reoxidation kinetics in the presence of EG. At concentrations of 50-70% EG, protein structural changes occur that include the release of the 16, 23, and 33 kDa extrinsic proteins and two of the catalytic Mn ions. For these samples, the capacity for O2 evolution is considerably reduced and the formation of donor side H2O2 is enhanced. In 60% EG, the nanosecond components in the rate of P680+ reduction are converted entirely to microsecond kinetics which upon return of the sample to the standard buffer medium are partially restored, indicating that EG has a reversible, solvent effect on the PSII donor side. At concentrations of EG > 70% chlorophyll fluorescence measurements reveal reversible increases in the FO level concomitant with the generation and disappearance of a 5 microseconds decay component in the P680+ reduction kinetics. This result may indicate a solvent-induced uncoupling of the light harvesting pigment bed from the reaction center complex. As the EG concentration is increased to 80-100%, there is an irreversible loss of the primary charge separation. The use of EG as a cryoprotectant and as a water-miscible organic solvent for PSII is discussed.

Sucrose and Glycerol Effects on Photosystem II

“…In intact thylakoids, but not in broken thylakoids, polyethylene glycol and sucrose were reported to increase the oxygen evolution rate (Ananev, 1988). Ethylene glycol concentrations above 50% have been shown to cause the loss of PSII extrinsic proteins and PSII oxygen evolving activity (Hillier et al, 1997). Taken together, this previous work implies that cosolvents can have several different effects on PSII.…”

“…A previous study has examined the effects of ethylene glycol on PSII (Hillier et al, 1997). In the presence of this cosolvent, there was no stimulatory effect on oxygen evolution.…”

Thomas John Wydrzynski (8 July 1947–16 March 2018)

“…When moving to RSBS in Canberra (Australia), Tom also had the innovative idea that an intact Mn-cluster or a small protein unit, carrying this cluster, can perhaps be isolated in non-aqueous solvents. Tom’s group thus studied for a while the effects of ethylene glycol on PSII (Hillier et al 1997).…”

Warwick Hillier: a tribute

“…He joined Tom's group in 1990 shortly after Tom had started his new position at the Research School of Biological Sciences at the ANU in Canberra, Australia. He helped Tom to set up his lab and worked during his Master's thesis among others on light-induced peroxide formation by salt-washed PSII preparations and on the effects of high concentrations of ethylene glycol on PSII (Hillier et al 1992;Hillier and Wydrzynski 1993;Wydrzynski et al 1996;Hillier et al 1997). In 1993 Johannes Messinger joined Tom's lab as a postdoc and established with the help of Murray Badger the instrumentation and the protocol for the measurement and analysis of the binding affinity of the two water molecules (substrate water) that are bound to the Mn 4 CaO 5 cluster in PSII in order to be oxidized to molecular oxygen (Messinger et al 1995a).…”