A phosphorylated 8 kDa protein of Chlamydomonas reinhurdii thylakoids has been isolated and its N-terminal amino acid sequence determined by gas-phase sequencing. The sequence analysis of the 48 amino acid residues revealed that this protein is about 50% homologous to the psb H gene products of higher plants. In contrast to them, it contains an insert of seven amino acid residues (Ser-5 to Lys-1 1). The first threonine residue was phosphorylated as determined by 32P detection during sequencing and also by analysis of the modified degradation products in the chemical reaction of the Edman degradation process. This latter method allows the identification of phosphorylated threonine residues without radiolabelling the protein. (Chlamydomonus reinhardiz)

The Qв-protein is as a hydrophobic integral membrane protein firmly bound in the reaction center complex of photosystem II. A new method was developed to purify the SDS extracted protein using reversed-phase chromatography with two binary linear gradient systems. The identification of the Qв-protein was achieved by its rapidly labeling during photoassimilation of [35S]sulfate and by its reaction with the photoaffinity label azido-[14C]atrazine. Furtherm ore, antisera against the purified Qв-protein reacted with a single peak fraction, the second peak of the chrom atogram , which was identical with the labeled protein peak fraction.

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