Plastoquinone B.

A compound found in spinach and other higher plants previously referred to as R 263 has now been found to be a breakdown product of plastoquinone B. This quinone, PQ B, is found with 8 other quinones in spinach chloroplasts. These 9 quinones are PQ A, PQ B, PQ C, PQ D (7, 8, 15) Vitamin K(1) (10, 12), an unknown naphthoquinone (13) and alpha-, beta- and gamma-tocopherylquinones (7, 12). An improved method for purification of plastoquinone B is described. Previous confusion of this compound with other quinoid material on silica gel is described and corrected R(F) values are given. The activity of PQ B is similar to the activity of PQ C in restoration studies of the photo-reduction of ferricyanide and indophenol.