Structural modification of gibberellins by in-vitro hydroxylating systems.

The behaviour of gibberellins A4, A5 and A7 (GA4, GA5 and GA7) has been studied in various in vitro hydroxylating systems. Incubation of GA4 and GA7 in peroxidase/dihydroxyfumarate or tyrosinase/ascorbate formulations resulted in the production of additional biologically-active zones on thin-layer chromatograms of the reaction mixtures. The product from GA7/peroxidase incubations was conclusively identified as GA7 norketone by gas/liquid chromatography-mass spectrometry and nuclear magnetic resonance spectrometry. A similar reaction is inferred for GA4 in the same system and for both GA4 and GA7 with tyrosinase/ascorbate. By analogy, the product derived from GA5 in the non-enzymatic ascorbate/ferrous iron system may be GA5 norketone. The reaction kinetics and the biological activity of the products are discussed.