On the biochemical basis of HCN production in the millipede Harpaphe haydeniana (Xystodesmidae: Polydesmida)

Abstract

Harpaphe haydeniana was shown to synthesize HCN and benzaldehyde in a manner similar to that of plants. By the injection of appropriate 14C precursors it was possible to isolate small quantities of the radioactive intermediates, phenylacetaldoxime, phenylacetonitrile, a glycoside of mandelonitrile, and mandelonitrile. The millipede stores a large droplet of D-mandelonitrile ((R)-mandelonitrile) in the storage vestibule of each cyanogenic gland.Mandelonitrile dissociates in vivo to HCN and benzaldehyde. The HCN is incorporated into β-cyanoalanine and asparagine. and benzaldehyde is oxidized to P-hydroxybenzoic acid.Two enzymes, β-glucosidase and α-hydroxynitrile lyase, were detected in paranotal extracts of H. haydeniana. The α-hydroxynitrile lyase is restricted to the reaction chamber of the cyanogenic gland and functions to promote the immediate release of HCN. It was also detected in freshly excreted glandular fluid of Oxidus gracilis, Sigmoria nantahalae, Cherokia georgiana, and Cleptoria rileyi. The pH of the fluid in these reaction chambers was found to be about 4, which corresponds to the pH optimum of the lyase.