Properties of the ammonia-lyases deaminating phenylalanine and related compounds in Triticum aestivum and Pteridium aquilinum

Abstract Wheat shoot acetone powders contain ammonia-lyases which catalyse the conversion of a number of ring-substituted phenylalanines to the corresponding cinnamic acids. The substrates deaminated, in decreasing order of efficiency, were l -phenylalanine, 3-fluoro-, 4-fluoro-, 3-hydroxy-, 4-hydroxy-, 3-methyl-, 3-methoxy-, 3,4-dihydroxy-, 3-methoxy-4-hydroxy-, and 4-methoxy-phenylalanine. Acetone powders from bracken gave similar results but were inactive with tyrosine, DOPA, 4-methoxy- and 3-methoxy-4-hydroxyphenylalanine. Acetone powders from both species were inactive with d -phenylalanine, d -tyrosine and a number of derivatives of phenylalanine. Studies on the thermolability and inhibition of the various activities suggest that two enzymes are responsible for the observed results. One of them ( l -phenylalanine ammonialyase E.C. 4.3.1.5) is relatively stable and has a broad substrate specificity whereas the other enzyme ( l -tyrosine ammonia-lyase) is less stable and fairly specific for l -tyrosine. Heat treatment of the crude enzyme from wheat gave a preparation active on l -phenylalanine but not on l -tyrosine. Attempts to get a preparation active with tyrosine, but not phenylalanine, were unsuccessful. Chromatography on DEAE-cellulose and Sephadex columns failed to separate these enzymes, but ammonium sulphate fractionation gave preparations in which the ratios of activities on phenylalanine to tyrosine varied from 4 to 20.