This enzyme, found in plants and cyanobacteria, catalyses a step in the synthesis of phylloquinone (vitamin K1), an electron carrier associated with photosystem I. The enzyme catalyses the transfer of the phytyl chain synthesized by EC 18.104.22.168, geranylgeranyl diphosphate reductase, to 2-carboxy-1,4-naphthoquinone.
mutant plants show pale-green young leaves and white old leaves. The ABC4 mutant plants contain no phylloquinone, and only about 3% plastoquinone. Photooxidation of P700 of PSI in the mutant is not observed, and the mutant has no P700. The maximum quantum yield of photosystem II in the ABc4 mutant is much decreased, and the electron transfer from PSII to PSI does not occur. The ultrastructure of the chloroplasts is almost the same as that of the wild-type plant. However, the chloroplasts in the albino leaves of the mutant are smaller and have a lot of grana thylakoids and few stroma thylakoids. The amounts of PSI and PSII core subunits in the mutant are significantly decreased
Recruitment of a foreign quinone into the A1 site of photosystem I. In vivo replacement of plastoquinone-9 by media-supplemented naphthoquinones in phylloquinone biosynthetic pathway mutants of Synechocystis sp. PCC 6803