Origin of cyanide in cultures of a psychrophilic basidiomycete.

An unidentified psychrophilic basidiomycete used valine and isoleucine as precursors to hydrocyanic acid (HCN). As probable intermediates in the pathway from valine and isoleucine two cyanogenic glucosides, linamarin and lotaustralin, were demonstrated in fungus cultures. The fungus contained two beta-glucosidases and an oxynitrilase which, acting together, were capable of releasing cyanide from both linamarin and lotaustralin. The two beta-glucosidases were purified and compared as to pH optimum, Michaelis constant, energy of activation, thermal stability, and substrate specificity. The products of methyl ethyl ketone cyanohydrin and acetone cyanohydrin dissociation by the oxynitrilase were demonstrated to be HCN together with methyl ethyl ketone and acetone, respectively. The oxynitrilase attacked aliphatic hydroxynitriles, but showed no activity on aromatic hydroxynitriles.