title: Thermal and solvent-isotope effects on the flagellar rotary motor near zero load.
abstract: In Escherichia coli, the behavior of the flagellar rotary motor near zero load can be studied by scattering light from nanogold spheres attached to proximal hooks of cells lacking flagellar filaments. We used this method to monitor changes in speed when cells were subjected to changes in temperature or shifted from a medium made with H(2)O to one made with D(2)O. In H(2)O, the speed increased with temperature in a near-exponential manner, with an activation enthalpy of 52 +/- 4 kJ/mol (12.0 +/- 1.0 kcal/mol). In D(2)O, the speed increased in a similar manner, with an activation enthalpy of 50 +/- 4 kJ/mol. The speed in H(2)O was higher than that in D(2)O by a factor of 1.53 +/- 0.14. We performed comparison studies of variations in temperature and solvent isotope, using motors operating at high loads. The variations were small, consistent with previous observations. The implications of these results for proton translocation are discussed.
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA.
authors.forename: Junhua
authors.initials: J
authors.lastname: Yuan
authors.forename: Howard C
authors.initials: HC
authors.lastname: Berg
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000502:physiology*; D001696:Biomechanical Phenomena / Q000502:physiology; D004926:Escherichia coli / Q000378:metabolism / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000502:physiology; D005407:Flagella / Q000502:physiology* / Q000648:ultrastructure; D015964:Gene Expression Regulation, Bacterial; D007554:Isotopes / Q000737:chemistry; D007700:Kinetics; D008564:Membrane Potentials / Q000502:physiology*; D020409:Molecular Motor Proteins / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D011522:Protons; D012964:Sodium / Q000502:physiology; D012997:Solvents; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D007554:Isotopes; D020409:Molecular Motor Proteins; D011522:Protons; D012997:Solvents; D014867:Water; D012964:Sodium