The Preparation of 14C-Labelled Gibberellic Acid

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Abstract
Gibberella fujikuroi was allowed to grow on unlabelled medium until gibberellic acid (GA) was being produced, and samples of mycelium were then transferred to a substrate containing C14-acetate. Pure C14-GA was isolated from the medium. The specific activity of the C14-GA was increased by transferring mycelium to a second labelled substrate 6 hr. after the first transfer. The specific activity was not increased when unlabelled glucose was present in the transfer medium, or when anaerobic conditions were maintained after transfer. Most of the C14-GA was produced during the 48 hr. following transfer. A large proportion of the C14 was lost as C14O2, and most of this was produced during the 40 hr. after transfer. After this period little GA was produced, but the evolution of unlabelled CO2 continued.