Identification of the Carboxyl-Terminal Processing Protease for the D1 Precursor Protein of the Photosystem II Reaction Center of Spinach

The enzyme involved in the carboxyl-terminal processing of theD1 precursor protein (pD1) of the photosystem II reaction centerwas purified from extracts of sonicated spinach thylakoids bya method that included chromatography on quaternary aminoethylanion-exchange, hydroxylapatite, copper-chelating affinity andgel-filtration columns. The enzyme was identified, from itschromatographic behavior, to be a monomeric protein of about45 kDa. The sequence of the amino-terminal 27 amino acids ofthis protein was determined directly, which exhibited low butappreciable (37%) homology to that deduced from a gene (ctpA)in Synechocystis sp. PCC 6803 that was proposed recently toencode the processing protease from results of genetic complementationanalysis. ³Present address: Asahi Kasei Chem. Co.