S. F. Yang studied the biosynthesis of Ethylene, a plant hormone involved in fruit ripening. A 1979 study with D. O. Adams established 1-aminocyclopropane-1-carboxylate as an intermediate between methionine and Ethylene.[ref]
In apple tissue, labelled methionine produced Ethylene in air but accumulated the cyclic intermediate under nitrogen. Supplying labelled 1-aminocyclopropane-1-carboxylate and comparing responses to an inhibitor helped establish the order of the reactions. The design used both precursor tracing and bypass of a blocked upstream step, rather than assuming that correlated concentrations reveal pathway order.[ref]
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