EFFECT OF CALCIUM-IONS ON THE SECONDARY STRUCTURES OF PHOTOSYSTEM-II AND ITS RELATIONS WITH PHOTOINHIBITION

Calcium ions play an important role in the oxygen-evolving process of photosystem II as demonstrated in many experiments. The changes of the secondary structures of PS II induced by the depletion of Ca2+ were r eported. The results indicated that the removal of Ca2+ led to the tra nsition of alpha-helix to turns and sheet structures. While Ca2+ was r e-added to the media, only the structures changed to turns could be re covered. The protein conformational changes of PS II during the donor side photoinhibition induced by the depletion of Ca2+ were also studie d. This showed that the protein conformational changes differed betwee n the control and Ca2+-depleted samples in a short period of illuminat ion (within 10 min). However, the changes became similar when the illu mination time was increased.