Oxygenic photosynthesis: EPR study of photosynthetic electron transport and oxygen-exchange, an overview

Abstract

In this review, we consider the applications of electron paramagnetic resonance (EPR) methods to the study of the relationships between the electron transport and oxygen-exchange processes in photosynthetic systems of oxygenic type. One of the purposes of this article is to encourage scientists to use the advantageous EPR oximetry approaches to study oxygen-related electron transport processes in photosynthetic systems. The structural organization of the photosynthetic electron transfer chain and the EPR approaches to the measurements of molecular oxygen (O 2) with O 2-sensitive species (nitroxide spin labels and solid paramagnetic particles) are briefly reviewed. In solution, the collision of O 2 with spin probes causes the broadening of their EPR spectra and the reduction of their spin-lattice relaxation times. Based on these effects, tools for measuring O 2 concentration and O 2 diffusion in biological systems have been developed. These methods, named "spin-label oximetry," include not only nitroxide spin labels, but also other stable free radicals with narrow EPR lines, as well as particulate probes with EPR spectra sensitive to molecular oxygen (lithium phthalocyanine, coals, and India ink). Applications of EPR approaches for measuring O 2 evolution and consumption are illustrated using examples of photosynthetic systems of oxygenic type, chloroplasts in situ (green leaves), and cyanobacteria.

The Interaction of Water-Soluble Nitroxide Radicals with Photosystem II

“…This effect can be explained by the light-induced evolution of O 2 dring illumination of PS II. Molecular oxygen is paramagnetic species ( 3 O 2 , spin S = 1), which can influence the relaxation properties of nitroxide radicals [35][36][37][38][39][40].…”

“…In the meantime, paramagnetic 3 O 2 molecules accelerate the spin-lattice relaxation of nitroxide radicals, thereby releasing the broadening of the EPR signal at high microwave power. Thus, 3 O 2 attenuates the broadening of the radical signals at high microwave power, leading to an increase in the signal amplitude [24,29,[36][37][38][39][40]. Comparing the timecourses of the light-induced changes in the EPR signal amplitude at P = 1 mW and P = 50 mW (Fig.…”