Oxygen evolution by Photosystem II: The contribution of backward transitions to the anomalous behaviour of double-hits revealed by a new analysis method

Abstract

Backward transitions in the analysis of oxygen production under flashing light were introduced by Packham et al., 1988, Photosynth. Res. 15: 221-232. In order to take backward transitions into account, a new method of analysis is presented: the 'eigenvalue method'. This method is based on the recurrence relation of oxygen production with four coefficients (also known as the four 'sigma' coefficients). It shows less susceptibility to round-off errors than other methods and permits the computation of double-hits directly from the coefficients, which was not possible before. With it we discovered that the inconsistent behaviour of double-hits observed previously under low flash intensities or low flash frequencies was mainly due to the inclusion of the backward transitions into the double-hit probability. In these conditions backward transitions seemed to be due either to the combination of an S-state deactivation and a miss, or to two S-state deactivations and a single-hit.In the presence of 3-(3, 4-Dichlorophenyl)-1, 1-dimethylurea (DCMU), the previous methods of 'sigma' analysis failed. In contrast, the new method resolved all four S-state probabilities; thus it has the further advantage of being more 'robust' (robustness being defined as the ability to yield a meaningful answer under difficult conditions).

Misses during Water Oxidation in Photosystem II Are S State-dependent

“…Already this result indicates that the miss factor varies with the S transitions as the average miss at for example 1°C in our experiment here (10%, Table 2) fits well with other data (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). However, if there is no miss in the first flash, there must be more misses in subsequent flashes.…”

“…1). These concepts are routinely used in the analysis of the S cycle, mostly in flash-induced oxygen evolution studies where it was introduced (19,20,(22)(23)(24)(25)(26)(27). They have also been used in the analysis of S cycle intermediates studied with EPR spectroscopy (28,35,36), transient optical spectroscopy, variable fluorescence (21,(41)(42)(43), and even EXAFS (30,31,33,34), reflecting S state-dependent structural changes.…”

“…S state-dependent misses were predicted from known equilibrium constants on the donor and acceptor sides of PSII (17,20) and, more recently, estimated from analysis of the flash-induced variable fluorescence yield (21). Despite this, an S state-independent miss parameter is used predominantly during analysis of the S cycle intermediates (19,(22)(23)(24)(25)27). There are two reasons for this (20).…”

“…In most studies, the S state cycle advancement has been probed by flash oxygen evolution measurements (19,20,(22)(23)(24)(25)(26)(27) which directly probe only the oxygen release in the S 3 3[S 4 ]3 S 0 step. The measured oxygen yield is then used to determine the miss factor which represents the average miss per state transition during the full S cycle because none of the other S state transitions can be measured directly.…”

High Sensitivity Proteomics Assisted Discovery of a Novel Operon Involved in the Assembly of Photosystem II, a Membrane Protein Complex

“…Data points were collected at intervals of 10 s during the flash train. These data were then analyzed utilizing the inhouse software program Oxygen Revolution, and peak data for each sample were fit to a four-step homogenous model of manganese cluster S-state cycling (23). Model-fitting calculations were done using MathCad software (MathSoft Engineering and Education, Inc., Cambridge, MA).…”