THE STRUCTURE AND FUNCTION OF THE 33 KDA EXTRINSIC PROTEIN OF PHOTOSYSTEM-II - A CRITICAL-ASSESSMENT

In this review the structure and function of the 33 kDa protein of Pho tosystem II is examined. Significant controversies exist concerning th e solution secondary structure of the protein, the location of its bin ding site(s) within Photosystem II, the amino acid residues of the 33 kDa protein required for binding and its stoichiometry within the phot osystem. The studies which examine these topics are considered from a critical perspective. A hypothetical model of the folding of the 33 kD a extrinsic protein which is supported by site-specific labeling studi es and site-directed mutagenesis experiments is presented. Additionall y, the function of the protein within the photosystem is unclear. We p resent a hypothesis that the 33 kDa protein is involved in maintaining the chloride associated with photosynthetic oxygen evolution in close proximity to the oxygen-evolving site.