Changes in the lateral distribution of the light‐harvesting chlorophyll‐a/b—protein complex induced by its phosphorylation

Abstract

The effect of protein phosphorylation on the distribution of chlorophyll‐protein complexes between appressed and non‐appressed thylakoid regions of spinach chloroplasts has been investigated. Stroma lamellae vesicles and inside‐out vesicles, representative of non‐appressed and appressed thylakoids, respectively, were isolated from thylakoid membranes before and after phosphorylation. The fractions were analyzed with respect to the yield of vesicles, incorporation of [³²P]phosphate into the light‐harvesting chlorophyll‐a / b—protein complex, chlorophyll composition, and the relative content of the main chlorophyll‐protein complexes. The yield of inside‐out vesicles from phosphorylated thylakoids was 20% lower than that from control thylakoids, indicating a partial destacking. The specific incorporation of [³²P]phosphate into the light‐harvesting chlorphyll‐a / b—protein complex was at least four times higher in stroma lamellae vesicles than in inside‐out vesicles. The proportion of the light‐harvesting chlorophyll‐a / b—protein complex in stroma lamellae vesicles increased from 13% to 21% of their total chlorphyll after phosphorylation of the thylakoids. There was also a corresponding increase in the level of chlorophyll b. These observations strongly suggest that phosphorylated light‐harvesting complexes migrate from appressed thylakoids rich in photosystem 2 to non‐appressed thylakoids rich in photosystem 1. In contrast, there was no evidence for a lateral migration of the chlorophyll‐a—protein complex of photosystem 2 after phosphorylation. Our results indicate that a lateral migration of phosphorylated light‐harvesting complexes in combination with a lateral separation of photosystem 1 and 2 to the different thylakoid regions, is a basis for the regulation of excitation energy between the two photosystems.