Two populations of the high-potential form of cytochrome b-559 in chloroplasts treated with 2-(3-chloro-4-trifluoromethyl)amino-3,5-dinitrothiophene (Ant 2p)

Abstract

Two populations of the high-potential form of cytochrome b-559 (cyt b-559HP) can be distinguished in chloroplasts. In the presence of ≥ 1 μM Ant 2p [2-(3-chloro-4-trifluoromethyl)anilino-3,5-dinitrothiophene] about one-half of the cyt b-559 is autooxidized in the dark. This fraction of cyt b-559HP undergoes rapid (t12≈2 ms) photoreduction followed by reoxidation in the dark with t12 100–200 ms. Photoreduction can be inhibited by DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and UHDBT [5-(n-undecyl)-6-hydroxy-4,7-dioxobezothiazole] but not by DBMIB (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinine), which suggests the involvement of QB or the plastoquinone pool. Another fraction of cyt b-559HP undergoes slow (t12 ≥ 1 s), irreversible photooxidation in the presence of ≥ 0.1 μM Ant 2p. The presently available data suggest that the heterogeneity of cyt b-559HP originates from PS IIα centers.