The deuterated substrates [4-2H2, 1-3H] geranyl pyrophosphate and [10-2H3, 1-3H] geranyl pyrophosphate were employed to examine isotopically sensitive branching in the biosynthesis of monoterpene olefin isomers. By this method,(−)-α-pinene and (−)-β-pinene were shown to be synthesized via a common intermediate by a single cyclization enzyme from grand fir (Abies grandis), as were (−)-(α-phellandrene and (−)-β-phellandrene by a ...