pH dependent inactivation of solubilized F1F0 ATP synthase by dicyclohexylcarbodiimide: pK(a) of detergent unmasked aspartyl-61 in Escherichia coli subunit c.
The pH dependence of the reaction of dicyclohexylcarbodiimide with the essential aspartyl-61 residue in subunit c of Escherichia coli ATP synthase was compared in membranes and in a detergent dispersed preparation of the enzyme. The rate of reaction was estimated by measuring the inactivation of ATPase activity. The reaction with the detergent dispersed form of the enzyme proved to be pH sensitive with the essential aspartyl group titrating with a pK(a)=8. However, when measured with E. coli membranes, the reaction proved to be pH insensitive. The results suggest that the reacting aspartyl-61 residues are shielded from the bulk aqueous solvent when in the membrane, but then become aqueous-accessible following detergent solubilization.
Valiyaveetil
Francis
F
Department of Biomolecular Chemistry, University of Wisconsin Medical School, 1300 University Avenue, Madison, WI 53706, USA.
Hermolin
Joe
J
Fillingame
Robert H
RH
D001224:Aspartic Acid / Q000737:chemistry; D002462:Cell Membrane / Q000187:drug effects; D003902:Detergents; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011092:Polyethylene Glycols; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000302:isolation & purification
D003902:Detergents; D004791:Enzyme Inhibitors; D001224:Aspartic Acid; D011092:Polyethylene Glycols; D004024:Dicyclohexylcarbodiimide; D006180:Proton-Translocating ATPases