The conversion of mevalonic acid into gibberellin A12-aldehyde in a cell-free system from Cucurbita pepo

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Abstract
A cell-free system prepared from immature seed of Cucurbita pepo incorporates the label from mevalonate-2-14C into ent-kaur-16-en-19-oic acid (I), ent-7α-hydroxy-kaur-16-en-19-oic acid (II), and ent-gibberell-16-en-7-al-19-oic acid (III) (gibberellin A12-aldehyde). The products were identified by gas liquid chromatography and by combined gas chromatography-mass spectrometry of the methylated and trimethylsilylated fractions. The radioactivity of the compounds was established by recrystallisation to constant specific radioactivity. Gibberellin A12 (IV), also detected in the system after incubation by combined gas chromatographymass spectrometry may be an artefact, derived from gibberellin A12-aldehyde by a non-enzymatic conversion. With gibberellin A12-aldehyde, the cell-free biosynthesis of an ent-gibberellane has been achieved for the first time.