A tryptophan decarboxylase from cucumber seedlings

The formation of tryptamine from tryptophan by extracts of cucumberhypocotyls is mediated by a tryptophan decarboxylase. The enzymerequires pyridoxal-5'-phosphate, and the pH optimum of thisenzyme is 7.0. The activity of the enzyme is inhibited by potassiumcyanide, but not by sodium azide or sodium fluoride; indicatingthat this enzyme is a decarboxylase rather than a peroxidase.The removal of contaminating epiphytic bacteria does not significantlyaffect the enzyme activity, and preincubation of enzyme extractsin streptomycin is also without effect. Neither aerobic noranaerobic cultures of internal bacteria which contaminate cucumberhypocotyb exhibit enzymic activity at pH 7.0. ¹Present address: P.O. Box 59 Prineville, Oregon 97754, U.S.A. (Received August 1, 1970; )