The nature of the starter unit for the rapamycin polyketide synthase

A remarkably high level of incorporation is observed when 2,2,5,5-tetradeutero -3,4- dihydroxycyclo -hexanecarboxylic acid is fed to the rapamycin-producing organism. Intriguingly, however, analysis of the gene sequence for the rapamycin polyketide synthase has suggested that the free acid may not normally be involved in rapamycin biosynthesis.