title: Thiol modification as a probe of conformational forms of the F1 ATPase of Escherichia coli and of the structural asymmetry of its beta subunits.
abstract: The sulfhydryl groups of soluble and membrane-bound F1 adenosine triphosphatase of Escherichia coli were modified by reaction with the fluorescent thiol reagents 5-iodoacetamidofluorescein, 2-[(4'-iodoacetamido)anilino]naphthalene-6-sulfonic acid 4-[N-(iodoacetoxy)ethyl-N-methyl]amino-7-nitrobenzo-2-oxa-1,3-d iaz ole and 2-[(4'-maleimidyl)anilino]naphthalene-6-sulfonic acid. Whereas gamma and delta subunits were always labeled by these reagents, the beta subunit reacted preferentially in the soluble enzyme, and the alpha subunit in the membrane-bound enzyme. This suggests that the soluble enzyme undergoes a conformational change on binding to the membrane. The three beta subunits of the soluble ATPase did not react with chemical reagents in a similar manner. One beta subunit was cross-linked to the epsilon subunit on treatment of the ATPase with 1-ethyl-3-[3-(dimethyl-amino)propyl]carbodiimide, as observed previously by Lötscher et al. [Biochemistry (1984) 23, 4134-4140]. A second beta subunit, which did not cross-link to the epsilon subunit, was modified preferentially by the fluorescent thiol reagents and by 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole. The third beta subunit was less chemically reactive than the others. Both alpha and beta subunits of the soluble 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole-modified enzyme were labeled by the fluorescent thiol reagents. Thus, the modified enzyme, which is inactive, probably has a different conformation from the native soluble ATPase.
authors.forename: H
authors.initials: H
authors.lastname: Stan-Lotter
authors.forename: P D
authors.initials: PD
authors.lastname: Bragg
mesh_terms: D009327:4-Chloro-7-nitrobenzofurazan; D002462:Cell Membrane / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology*; D011487:Protein Conformation; D006180:Proton-Translocating ATPases / Q000032:analysis*; D012995:Solubility; D013050:Spectrometry, Fluorescence; D013438:Sulfhydryl Compounds / Q000032:analysis*; D013439:Sulfhydryl Reagents
chemical_list: D013438:Sulfhydryl Compounds; D013439:Sulfhydryl Reagents; D006180:Proton-Translocating ATPases; D009327:4-Chloro-7-nitrobenzofurazan