A novel magnesium-dependent mechanism for the activation of transducin by fluoride.
Activation of transducin-GDP by NaF is mainly mediated by aluminofluorde or beryllofluoride complexes acting as GTP gamma-phosphate analogs. In millimolar magnesium, NaF at concentrations above 3 mM is active even in the absence of aluminium or beryllium. This activation has a Hill coefficient of 3 with respect to F-, and its rate is linear with respect to Mg2+ concentrations above 2 mM. Upon fluoride dilution, inactivation rate is hundreds of times faster than for aluminofluoride-activated T alpha GDP. We propose that at high NaF concentrations, 3 hydrogen-bonded fluorides in the gamma-phosphate site of T alpha GDP entrap a magnesium counterion and this induces the transconformation to the T alpha GTP form.
Antonny
B
B
CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, Valbonne, France.
Bigay
J
J
Chabre
M
M
D000535:Aluminum / Q000494:pharmacology; D017607:Aluminum Compounds; D000818:Animals; D001608:Beryllium / Q000502:physiology; D002417:Cattle; D004789:Enzyme Activation / Q000187:drug effects*; D005459:Fluorides / Q000494:pharmacology*; D006153:Guanosine Diphosphate / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000502:physiology*; D012374:Rod Cell Outer Segment; D013050:Spectrometry, Fluorescence; D015293:Transducin / Q000378:metabolism*
D017607:Aluminum Compounds; D006153:Guanosine Diphosphate; D000535:Aluminum; D015293:Transducin; D008274:Magnesium; D001608:Beryllium; D005459:Fluorides; C032311:aluminum fluoride