Purification and Identification of Thylakoid Protein Kinase(s) that Phosphorylates Isolated Lhcii and CP43 of Photosystem II

Abstract

Redox-controlled phosphorylation of thylakoid proteins plays a major role in the PSIl dynamic processes related to light-induced turnover of the reaction center D 1 (D2) proteins and the regulation of energy distribution between the two photosystems [1, 2]. The activation of the redox-controlled protein-kinase is regulated by the interaction of reduced plastoquinone with the quinol oxidation site of the cytochrome bf complex [3]. Despite many efforts to isolate the thylakoid protein kinase(s) and identify its molecular nature [2] the identity of the redox-controlled enzyme(s) is still unknown. Two putative kinase bands of 67 and 53 kDa were identified by renaturation of SDS-PAGE resolved proteins [4] of a crude thylakoid cytochrome bf preparation, that was shown before to be enriched in protein-kinase activity [5, 6]. Here we report the further purification of a solubilised protein kinase highly enriched in activity, that phosphorylates isolated LHCII as well as the CP43 protein of isolated PSII-core preparations.