Farnesyl pyrophosphate synthetase. Mechanistic studies of the 1'-4 coupling reaction with 2-fluorogeranyl pyrophosphate.
The mechanism of the 1'-4 coupling reaction between isopentenyl pyrophosphate and geranyl pyrophosphate catalyzed by farnesyl pyrophosphate synthetase from porcine liver was studied with the allylic substrate analogue 2-fluorogeranyl pyrophosphate. 2-Fluorogeranyl pyrophosphate is an alternate substrate for the enzyme, yielding 6-fluorofarnesyl pyrophosphate upon condensation with isopentenyl pyrophosphate. The Michaelis constant for the fluoroanalogue, Km = 1.1 micron, is similar to that measured for geranyl pyrophosphate, Km = 0.7 micron. However, the rate of condensation with the fluoroanalogue was only 8.4 X 10(-4) that of the normal reaction. A similar rate of depression (4.4 X 10(-3)) was found for solvolysis of geranyl methanesulfonate and the corresponding 2-fluoro derivative, reactions known to proceed via cationic intermediates. In contrast, displacement of chlorine from geranyl chloride and 2-fluorogeranyl chloride by cyanide showed a small (2-fold) rate enhancement for the fluoro compound. Finally, 2-fluorogeranyl pyrophosphate is a competitive inhibitor against geranyl pyrophosphate. These data are interpreted in terms of an ionization-condensation-elimination mechanism for the 1'-4 coupling reaction.
D000818:Animals; D004122:Dimethylallyltranstransferase / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D013058:Mass Spectrometry; D009943:Organophosphorus Compounds / Q000378:metabolism; D011106:Polyisoprenyl Phosphates; D011485:Protein Binding; D013329:Structure-Activity Relationship; D013552:Swine; D013729:Terpenes / Q000378:metabolism*; D014166:Transferases / Q000378:metabolism*
D009943:Organophosphorus Compounds; D011106:Polyisoprenyl Phosphates; D013729:Terpenes; C017877:2-fluorogeranyl pyrophosphate; D014166:Transferases; D004122:Dimethylallyltranstransferase