Biosynthesis and Structure of a New Intermediate between Farnesyl Pyrophosphate and Squalene

The intermediate, discovered by Rilling, between farnesyl pyrophosphate and squalene was synthesized in milligram quantities with yeast subcellular particles from farnesyl-14C-pyrophosphate and from farnesyl-1-3H2-14C-pyrophosphate. The 3H:14C ratio in the new squalene precursor was found to be identical with that in the farnesyl pyrophosphate, whereas the ratio in squalene was close to the expected value of 0.75 relative to the ratio either in farnesyl pyrophosphate or in the precursor. The squalene precursor is optically active and gives a normal optical (dextro) rotatory dispersion curve. From nuclear magnetic resonance and mass spectrometric studies, and from chemical degradation, it is concluded that this squalene precursor is the cyclic pyrophosphoryl ester of squalene-10,11-glycol. The metabolism of farnesyl pyrophosphate by the yeast subcellular particles yields, in addition to the squalene precursor, free farnesol, some nerolidol, farnesene, and also the cyclic monophosphate (phosphodiester) of squalene-10,11-glycol. The latter is not converted into squalene with liver microsomes and NADPH. The synthesis of the squalene precursor from farnesyl pyrophosphate with liver microsomes could not be shown. In the absence of NADPH, liver microsomes converted farnesyl pyrophosphate quantitatively into farnesol, nerolidol, and the phosphodiester of squalene-10,11-glycol, which is thought to arise by enzymic hydrolysis of the precursor. A new method for the preparation of crystalline farnesyl pyrophosphate and for the purification of the squalene precursor is described.