Carotenoid‐binding proteins of photosystem II

Abstract

The distribution of the photosynthetic pigments of the chlorophyll‐binding proteins or photosystem‐II membranes, isolated from dark‐adapted maize leaves was determined. Most (80%) of a xanthophyll, violaxanthin, was found in the three minor chlorophyll‐a/b proteins CP24, CP26 and CP29 whose function is unknown. Violaxanthin is the precursor of zeaxanthin, which is involved in dissipating excess excitation energy into heat [Demming‐Adams, B. (1991) Biochim. Biophys. Acta 1020, 1–24] under conditions of high transmembrane pH gradient [Gilmore, A. M. & Yamamoto, H. Y. (1992) Proc. Natl Acad. Sci. USA 89, 1899–1903]. We propose that a role for the minor photosystem‐II chlorophyll‐a/b proteins is the regulation of energy transfer to the reaction centre. It was also confirmed that the photosystem II reaction centre (D1‐D2‐cytochrome b559) contains β‐carotene as the only carotenoid. However, the two other chlorophyll‐a‐binding proteins of photosystem II, CP47 and CP43, bind not only β‐carotene, but also the xanthophyll lutein, previously thought to be restricted to chlorophyll‐a/b proteins. Copyright © 1993, Wiley Blackwell. All rights reserved