title: Interaction of mant-adenosine nucleotides and magnesium with kinesin.
abstract: Displacement of the fluorescent substrate analogue methylanthraniloyl ADP (mant-ADP) from kinesin by excess ATP results in a biphasic fluorescent transient. The pH and microtubule dependence of the rates and amplitudes indicates that the two phases are produced by release of bound mant-ADP, with an excess of the 3'-isomer, followed by the subsequent relaxation of the free 2'- and 3'-isomers to their equilibrium distribution. The first phase for release of mant-ADP is accelerated by microtubules and occurs at the same rate as ADP release measured using [32P]ADP. The second phase is subject to base catalysis and occurs at the same rate as the isomerization of isolated 2'- or 3'-mant-ATP over a 100-fold range of rates. The bound mant-ADP isomers undergo isomerization rapidly when bound to kinesin at pH 8.2, whereas mant-ADP isomers interconvert only slowly when bound to myosin. No fluorescence resonance energy transfer occurs between the single tryptophan in the kinesin neck domain and bound mant-ADP, but efficient energy transfer does occur from protein tyrosine groups. The rate of mant-ADP release in the absence of microtubules is minimal (0.005 s-1) at pH 7-8, 2 mM Mg2+, and 25 mM KCl but is accelerated at lower pH (0.04 s-1 at pH 5.5) and either lower or higher [KCl] (0.01 and 0. 06 s-1 at 0 and 800 mM KCl, respectively). The microtubule-stimulated rate of ADP release is accelerated at low pH and inhibited by high concentrations of monovalent salts. Reduction of the free Mg2+ by addition of excess EDTA increases the release of mant-ADP from E.MgADP to 0.03 s-1. This acceleration at low Mg2+ likely represents sequential release of Mg2+ at 0.03 s-1 followed by rapid release of ADP, as the rate of ADP release from Mg-free E.ADP is fast (>0.5 s-1). At high Mg2+, rebinding of Mg2+ to E.ADP forces release of ADP from the E.MgADP complex at 0.005 s-1.
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: J Q
authors.initials: JQ
authors.lastname: Cheng
authors.forename: W
authors.initials: W
authors.lastname: Jiang
authors.forename: D D
authors.initials: DD
authors.lastname: Hackney
mesh_terms: D000244:Adenosine Diphosphate / Q000031:analogs & derivatives* / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D004330:Drosophila; D004735:Energy Transfer; D005456:Fluorescent Dyes; D006801:Humans; D007536:Isomerism; D016547:Kinesins / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D008956:Models, Chemical; D008958:Models, Molecular; D015879:Myosin Subfragments / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D014466:Ultraviolet Rays; D062367:ortho-Aminobenzoates / Q000378:metabolism*
chemical_list: D005456:Fluorescent Dyes; D015879:Myosin Subfragments; D010446:Peptide Fragments; D062367:ortho-Aminobenzoates; D000244:Adenosine Diphosphate; C081523:3'-O-(N-methylanthraniloyl)adenosine 5'-diphosphate; C045473:3'-O-(N-methylanthraniloyl) ATP; D000255:Adenosine Triphosphate; D016547:Kinesins; D008274:Magnesium