Maize Phenylalanine Ammonia-Lyase Has Tyrosine Ammonia-Lyase Activity

Abstract

A full-length cDNA encoding phenylalanine ammonia-lyase (PAL) from Zea mays L. was isolated and the coding region was expressed in Escherichia coli as a C-terminal fusion to glutathione S-transferase. After purification by glutathione-Sepharose chromatography, the glutathione S-transferase moiety was cleaved off and the resulting PAL enzyme analyzed. In contrast to PAL from dicots, this maize PAL isozyme catalyzed the deamination of both i-phenylalanine (PAL activity) and i-tyrosine (tyrosine ammonialyase activity). These results provide unequivocal proof that PAL and tyrosine ammonia-lyase activities reside in the same polypeptide. In spite of large differences in the Michaelis constant and turnover number of the two activities, their catalytic efficiencies are very similar. Also, both activities have the same p H and temperature optima. These results imply that maize can produce p-coumaric acid from both phenylalanine and tyrosine.PAL (EC 4.3.1.5) catalyzes the elimination of ammonia from L-Phe to yield (E)-cinnamic acid ( Fig. 1) (Koukol and Com, 1961), the first step in the phenylpropanoid pathway (for reviews, see Hahlbrock and Scheel, 1989;Dixon and Paiva, 1995;Whetten and Sederoff, 1995;Campbell and Sederoff, 1996). PAL activity has been found in some fungi and in a11 higher plants analyzed but not in animals. Because of the central function of PAL at a branch point of metabolism, this enzyme is one of the best studied in plants; the same is true for its corresponding gene(s).In a11 plants analyzed, PAL has been shown to occur as a tetramer, and multiple forms have often been isolated (Bolwell et al., 1985). PAL multigene families, such as those in tomato (Lycopersicon esculentum; Lee et al., 1992), parsley (Petroselinum crispum; Appert et al., 1994), or Arabidopsis thaliana (Wanner et al., 1995), explain at least in part these different forms. The occurrence of heteromers is likely but has as yet not been proven. On the other hand, apparent charge isoforms of a poplar PAL were recovered from insect cell cultures producing the protein from a baculovirus expression vector containing the respective cDNA (McKegney et al., 1996).Results from severa1 studies (Neish, 1961; Young et al., 1966;Havir et al., 1971;Jangaard, 1974) indicated that the enzyme from monocots utilizes Tyr (TAL activity) in addition to Phe, whereas the enzyme from dicots utilizes only Phe efficiently. The four homotetrameric parsley PAL (Havir et al., 1971), indicating that PAL from maize also has TAL activity. However, the uncertainty remains that a protein with TAL activity copurifies with PAL activity. Referring to the heterologous expression of parsley PAL cDNAs (Schulz et al., 1989; Appert et al., 1994), Whetten and Sederoff (1995) stated: "The same experiment could be performed with maize cDNA to test for PAL and TAL activities in the same polypeptide." This is exactly the experiment we report here. Expression of a PAL-specific cDNA from maize in Escherichia coli provided the ultimate proof that PAL and TAL activities reside in ...

Effects of Nitrogen Fertilizer and Planting Density on the Lignin Synthesis in the Culm in Relation to Lodging Resistance of Buckwheat

“…PAL is a rate-limiting enzyme in the shikimic acid pathway, and it catalyzes the conversion of L-phenylalanine dehydrogenase into trans cinnamic acid (Sewalt et al, 1997). TAL catalyzes the conversion of tyrosine into coumaric acid, which only exists in gramineous plants (Rösler et al, 1997). 4CL a ligase in lignin metabolism, catalyzes the conversion of cinnamic acid into the corresponding esters (Lee et al, 1997).…”

Induction of Phenolic Compounds in Wheat (Triticum aestivum L.) Tissue Cultures by Streptomycin

“…The key step in biosynthesis of the phenylpropanoid skele-ton in higher plants is the deamination of l-phenylalanine to yield trans-cinnamic acid and ammonia, a reaction catalyzed by PAL (Rösler et al, 1997).…”

Biochemical Evaluation of Phenylalanine Ammonia Lyase (PAL) from Endemic Cyathobasis fruticulosa (Bunge) Aellen. for the Dietary Treatment of Phenylketonuria (PKU)

“…The enzyme does not use any cofactor (7). Although certain fungi and higher plants possess PAL activity, no animal has been shown to have this enzyme yet (8). Being one of several commercially available non-hydrolytic enzymes, plant PAL has been successfully utilized to treat certain neoplasms in mice as well as to measure serum levels of Phe in humans with PKU and diets low in Phe (9).…”