Open AccessThe Control of the Adenosine Triphosphatase of Rhodospirillum rubrum Chromatophores by Divalent Cations and the Membrane High Energy State
Author(s) -
EDWARDS Patricia A.,
JACKSON J. Barry
Publication year - 1976
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1976.tb10091.x
Subject(s) - divalent , rhodospirillum rubrum , chemistry , magnesium , atp hydrolysis , substrate (aquarium) , calcium , hydrolysis , membrane , adenosine triphosphate , chromatophore , enzyme , biophysics , inorganic chemistry , biochemistry , atpase , biology , organic chemistry , ecology , fishery
1 The rate of ATP hydrolysis, catalysed by Rhodospirillum rubrum chromatophores is accelerated by low concentrations and inhibited by high concentrations of uncoupling agent. 2 The inhibition at high concentrations of uncoupling agent is potentiated by the presence of free magnesium ions. At low uncoupler concentrations magnesium has no effect on the rate of ATP hydrolysis. 3 Inhibition of ATP hydrolysis by high concentrations of uncoupling agent and free magnesium ions is reversed by illumination. Illumination has less effect at low magnesium concentrations. 4 Free calcium ions inhibit ATP hydrolysis independently of the coupled state of the membrane. 5 Under coupled conditions, magnesium ions can overcome the inhibition induced by calcium. The two ions compete for the same site on the enzyme. 6 Inhibition by free magnesium in highly uncoupled chromatophores and inhibition by free calcium are both non‐competitive with respect to the divalent cation‐ATP substrate. 7 These data are consistent with a model in which divalent cations can bind to a site on the enzyme which is distinct from the substrate site. The regulation of the enzyme activity by the high energy state of the membrane is dependent on the occupant of this site.