Difference FT-IR of Chlamydomonas reinhardtii photosystem II in the presence and absence of the manganese stabilizing protein

Abstract

The photosystem II protein catalyzes the reduction of plastquinone and the splitting of water to produce O2. The site of water oxidation is composed of a variety of inorganic cofactors, including manganese, calcium, and chloride. Oxygen production requires four oxidations of the site; the intermediates of these oxidation reactions are called the S states. The manganese stabilizing protein is necessary for efficient catalytic turnover of water oxidation. This subunit is believed to be in close proximity to bound manganese atoms. It has been previously shown using light-induced difference Fourier transform infrared spectroscopy (FT-IR) that the manganese stabilizing protein undergoes a conformational change during the S1 to S2 transition. The aspartic acid and/or glutamic acid residues on Spinach MSP undergo a protonation change. Here, we have used FT-IR to study the S state transitions of the photosystem II protein both containing and depleted of the manganese stabilizing protein isolated from Chlamydomonas reinhardtii. Our results indicate that the Chlamydomonas photosystem II protein has similar infrared absorbance changes during the S1 to S2 transition as that of photosystem II isolated from Spinach. Differences between the FT-IR spectra of MSP containing and MSP minus photosystem II will be discussed.