Open AccessFerricyanide Reduction in Photosystem II of Spinach Chloroplasts
Author(s) -
Rita Barr,
F.L. Crane
Publication year - 1981
Publication title -
plant physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.554
H-Index - 312
eISSN - 1532-2548
pISSN - 0032-0889
DOI - 10.1104/pp.67.6.1190
Subject(s) - ferricyanide , chemistry , photosystem ii , spinach , chloroplast , photosystem i , photosynthesis , trypsin , thylakoid , photochemistry , biochemistry , enzyme , gene
Ferricyanide can be reduced in Photosystem II of spinach chloroplasts at 2 separate sites, both of which are sensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea, but only one of which is sensitive to dibromothymoquinone. Data presented in this paper emphasize ferricyanide site II of Photosystem II, which is sensitive to thiol inhibition and may reflect a cyclic pathway around Photosystem II. Ferricyanide reduction sites 1 and 2 also differ from each other in fractions isolated from discontinuous sucrose gradients, from fragmented chloroplasts, and upon trypsin treatment. Sucrose density gradient centrifugation shows that ferricyanide reduction site 1 activity at pH 6 decreases from 30 to 50% in various isolated fractions, while the dibromothymoquinone-insensitive activity at pH 8 (site 2) is stimulated from 15 to 35%.Fragmentation of chloroplasts also stimulates ferricyanide site II activity, but trypsin treatment destroys ferricyanide reduction site II completely in 6 minutes. Ferricyanide reduction site 1 still retains 50% activity at this point. The meaning of these differences is discussed in terms of the physical location of these two sites on the thylakoid membrane.