The late C6 oxidation pathway

Nevertheless, there are many questions still open because of problems to detect enzyme activities corresponding to each step of the pathway. The model of biosynthesis pathway was put together by studying the metabolism of exogenously applied intermediates in cell cultures of various origins and combining these results with data of native brassinosteroid patterns. It is more or less accepted that there are three pathways in parallel, the early and the late C6 oxidation pathway, as well as the 24/ -epimers follow ing the same route. Some observations in the analysis of native brassinosteroid patterns suggest a possible connection between the pathways. It was shown that seeds of Arabidopsis contain castasterone and 24-epi-brassinolide [34]. Also members of both 24-epimers, brassinolide and 24-epi-brassinolide were detected in tomato seeds [Winter, unpublished]. 

Fig. 3. Biosynthesis of brassinolide from campesterol. Brassinolide is synthesized from castasterone which is derived from campestanol by either late C6-oxidation pathway or early C6-oxidation pathway. Campesterol is converted to campestanol by hydrogenation. Italic letters refer to the lesions in the biosynthesis and sensitivity mutants of Arabidopsis det2, dwf4, cpd and bril) and pea (Ik and Ika). The asterisked pathways and compounds are hypothetical.

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