A Tribute to Graham Wesley Butler, FRS

Eric E Conn, Professor Emeritus, University of California, Davis.

Member of the National Academy of Science, USA.

Graham Butler was a major contributor to the renewal of interest in the biosynthesis of cyanogenic glycosides by higher plants in the early 1960s. Hydrogen cyanide is released from these compounds when the tissue is damaged (eg. by insects or maceration). Graham’s interest in cyanogenesis arose from the fact that white clover, used in New Zealand, had been blamed for production of goiters in sheep feeding on clover pastures. He and his wife Beris co-authored a paper in Nature in 1960 showing that the two glycosides in clover are formed from the amino acids valine and isoleucine.

When Graham learned that similar research was being done in our group at the University of California at Davis, he arranged to spend a study leave there with me in 1961-1962.

There he was responsible for introducing flax seedlings (Linum utillitissum) and the use of their etiolated excised shoots, which produce large amounts of cyanogenic glucosides, as an experimental tissue, and readily confirmed that valine and isoleucine were precursors. (Later, when I took sabbatical leave in Graham’s lab in 1965-66, this plant was used almost exclusively as the biosynthetic tissue of choice.) After some five years of endeavour in my and Graham’s laboratories, his PhD student, Brian Tapper, found that oximes were converted to the respective cyanogenic glucoside (published with E Conn and G Butler in 1967)

An interesting and related discovery that Graham made while in California in 1961 was that ¹⁴C-labeled HCN fed to flax and sorghum seedlings was converted rapidly and exclusively into the amide carbon of asparagine with β-cyanoalanine as an intermediate. Many years later, Shang-fa Yang, studying the metabolism of the plant hormone ethylene, showed that one molecule of HCN is produced for every molecule of ethylene formed in plants. Consequently the biosynthesis of asparagine from HCN, discovered by Graham in cyanogenic plants, is now considered to be the mechanism in all plants for the removal of the HCN formed during ethylene biosynthesis.