Spectroscopic study of the light-induced changes of the core antenna complex CP43 in photosystem II

In this study, spectroscopic approaches were used to evaluate light-induced changes in chlorophyll protein 43 (CP43). Upon illumination, we observed chlorophyll (Chl) a bleaching with the complete opening of the tetrapyrrole ring. Electronic transition frequencies to different energy levels of the second singlet electronic state (S2) were changed. In addition, we observed altered rotational and vibrational transitions of Chl a and the CP43 apoprotein as well as variations in the microenvironment surrounding Chl a. CP43 contains three beta-carotene (beta-Car) and five Chl a molecules, which are involved in the energy transfer from beta-carotene to Chl a. We found that these five Chl a molecules bleached more readily than others under constant illumination, with energy transfer from beta-Car to Chl a being continuously lost as illumination continued.