1. The incorporation of [2-14C]acetate, [2-14C]mevalonic acid and [2-14C,2-3H2]-mevalonic acid into torulene and torularhodin by Rhodotorula rubra and Rhodotorula glutinis was studied. 2. A recovery of 14.3% of the label was obtained on decarboxylation of the torularhodin biosynthesized from [2-14C]mevalonic acid. 3. An analysis of the 3H/14C ratio in torularhodin gave a value of 9.44:8. 4. These results, obtained by different experimental techniques, show that the reactions in the conversion of the dimethyl group of isopentenyl pyrophosphate into the 16′,17′-position of torularhodin must be free from randomization. A mechanism for the isomerization of isopentenyl pyrophosphate to dimethylallyl pyrophosphate is suggested.
