Evidence for active and inactive forms of L-phenylalanine ammonia-lyase in etiolated and light-grown radish cotyledons

Purification, characterization and induction of L-phenylalanine ammonia-lyase in Phaseolus vulgaris

The enzyme L-phenylalanine ammonia-lyase was purified from leaves of Phaseolus vulgaris by Sephacryl S-200 gel filtration and Sepharose-4-B--succinyl-aminoethyl-L-phenylalanine affinity chromatography. L-Phenylalanine ammonia-lyase was specifically eluted from the affinity matrix with its substrate L-phenylalanine at 20-25 degrees C. The purified enzyme was shown to be homogeneous by gel electrophoresis both in presence and absence of SDS. Its Mr, determined by gel filtration and non-denaturing gel electrophoresis, was 320,000 +/- 9000 and 330,000 +/- 4000 respectively. After SDS electrophoresis only one band of Mr 83,000 +/- 4000 was detected, indicating that the enzyme is an oligomer containing four subunits. The pH optimum of enzyme activity was 8.8-9.2. Ampholyte isoelectrofocusing in polyacrylamide demonstrated the presence of a single charged species at pH 4.2. The homogeneous enzyme catalyzed the deamination of L-phenylalanine to trans-cinnamate but did not catalyze the transamination of L-phenylalanine to L-phenylpyruvate. The enzyme showed Km 1.25 mM for L-phenylalanine. Antibodies to homogeneous L-phenylalanine ammonia-lyase recognised specific epitopes on L-phenylalanine aminotransferase as demonstrated by immunoaffinity purification and immunoblotting. The induction of L-phenylalanine ammonia-lyase activity during phaseollin biosynthesis in the Phaseolus vulgaris--Colletotrichum lindemuthianum interaction was regulated by an increase in enzyme concentration resulting from an increase in de novo synthesis of L-phenylalanine ammonia-lyase protein.

Properties of L-phenylalanine ammonia-lyase and turnover rate in etiolated and far-red illuminated seedlings of radish

1. L-Phenylalanine ammonia-lyase (EC 4.3.1.5) was purified from radish cotyledons. The adsorption of the enzyme on L-phenylalanine-Sepharose 4B was nonspecific; the present data disprove the conclusions reached previously (Blondel, J.D., Huault, C., Faye, L., Rollin, P. and Cohen, P. (1973) FEBS Lett. 36, 239-244). 2. The apparent molecular weight of the enzyme fluctuated according to pH and ionic strength. A mean value of 290 000 was determined for the 'native' form. The activation energy was 54.4 kJ/mol. L- and D-phenylalanine protected the lyase from sodium borohydride denaturation. 3. Two Michaelis constants, KHm = 1.5 x 10(-5) M and KLm = 9.5 x 10(-5) M, were determined. The Hill coefficient value (h) was 0.48. This coefficient was 0.6 for cinnamate inhibition. These results suggest that phenylalanine ammonia-lyase in radish cotyledons is regulated by a negative cooperativity mechanism. 4. The phytochrome-mediated increase in phenylalanine ammonia-lyase activity was investigated by density labelling with 2H2O followed by isopycnic centrifugation in KBr gradients. An apparent half-life of 3.5 h was found for both the enzyme extracted from etiolated or far-red irradiated cotyledons. 5. Provided that phytochrome does not control the availability of labelled amino acids for protein synthesis, the present results are consistent with a far-red light-induced increase in the rate of synthesis of the lyase in radish cotyledons.

Purification to homogeneity and some properties of L-phenylalanine ammonia-lyase of irradiated mustard (Sinapis alba L.) cotyledons

1. Lyase (L-Phenylalanine ammonia-lyase, EC 4.3.1.5) from far-red light-irradiated mustard cotyledons was purified to a single protein using ammonium sulphate fractionation, column chromatography on L-phenylalanyl-Sepharose 4B and on Sephadex G-200, isoelectric focusing and polyacryalmide gel electrophoresis. 2. The enzyme constituted 0.01% of total cellular protein, did not catalyse the deamination of L-tyrosine, had a pH optimum of pH 8.6 and an isoelectric point of pH 5.6. 3. The sedimentation coefficient was estimated as 11.3 S, the Stokes' radius 4.25 nm, and the molecular weight 240 000 +/- 9000 (S.E.). 4. Electrophoresis on denaturing polyacrylamide gels gave a single stained protein band corresponding to a subunit molecular weight of 55 000 indicating a tetrameric structure of equal (or near-equal) size subunits. 5. Maximum velocity (V) for the purified lyase at 25 degrees C was 3.83--4.10 nkat. 1(-1) enzyme and Km value 0.151--0.154 mM. Negative cooperativity (Hill coefficient, n = 1.08) was not detected over the substrate concentration range tested. 6. A putative non-diffusible inhibitor isolated from dark-grown gherkin hypocotyls inhibited the homogeneously purified mustard lyase.

A specific and reversible macromolecular inhibitor of phenylalanine ammonia-lyase and cinnamic acid-4-hydroxylase in gherkins

A non-dialysable inhibitor of phenylalanine ammonia-lyase (L-phenylalanine ammonia-lyase, EC 4.3.1.5) has been partially purified from dark-grown gherkin hypocotyls. On extraction of tissue it is found both in the soluble (106 000 X g supernatant) and microsomal (106 000 X g pellet) fractions and can be extracted from the microsomal membranes with 10 mM sodium cholate and 1 M KCl. The soluble and microsomal fractions have similar properties, suggesting the presence of the same active component. The inhibitor is small (Mr less than 20 000), thermolabile, sensitive to proteolytic digestion, and apparently hydrophobic. Purification of the inhibitor was achieved by chromatography on DEAE-cellulose by gel filtration on Sephadex G-50. The inhibitor preparations inhibit phenylalanine ammonia-lyase isolated from a number of plant tissues and also cinnamic acid-4-hydroxylase (trans-cinnamate, NADPH:oxygen oxidoreductase (4-hydroxylating), EC 1.14.13.11) from gherkins and peas, but not a wide range of other enzymes. The evidence suggests that inhibition of the two enzymes is due to the same substance, but this has not yet been confirmed. Kinetic experiments show that the inhibitor is competitive with phenylalanine for the lyase and that its association with the lyase is reversible. Further, a mixture of inhibitor and lyase can be separated on non-denaturing polyacrylamide gels without loss of lyase activity. The activities of phenylalanine ammonia-lyase and cinnamic acid 4-hydroxylase are often concurrently regulated and both have regulatory roles in phenol metabolism; it is suggested that the inhibitor may be specifically involved in controlling their activities in vivo.

[Photoregulation of L-phenylalanine ammia-lyase: an immunochemical approach]

The photoregulation of L-Phenylalanine ammonia-lyase (PAL) is studied by immunochemical methods. We used a partly purified L-Phenylalanine ammonia-lyase: F1 light fraction, the corresponding inactive one provided from dark-grown cotyledons: F1 dark fraction and the antisera specific of these two fractions. The complete absorption of PAL activity from F1 light fraction with the anti-F1 light immune serum shows the antigenicity of PAL and the specificity of this serum for all forms of PAL present in F1 light fraction. The presence of an inactive L-Phenylalanine ammonia-lyase in the 36 h dark-grown cotyledons suggested by preliminary results of absorption is conformed by showing that less PAL activity is precipitated from the fraction F1 light by a same amount of IgG anti-F1 light when F1 dark fraction is added. This result is explained by a competition between active and inactive forms of PAL for the IgG extracted from an immune serum specific for F1 light fraction. By measuring the absorption of PAL activity from FO fraction (crude extract) obtained from 18 h, 36 h and 48 h light-grown cotyledons when increasing amounts of IgG anti-F1 36 h light are added, we demonstrate the presence of at least two isozymes A and B, the synthesis of B being shifted in time in comparison to A.

Regulation of L-phenylalanine ammonia-lyase from Rhizoctonia solani

Maximal levels of L-henylalanine ammonia-lyase activity were observed when the mycelial felts of Rhizoctonia solani were grown for 4.5 days on Byrde synthetic medium containing 3.5% glucose and 0.3% L-phenylalanine, Differential centrifugation studies have indicated that the enzyme is localized in the soluble fraction. The time course of induction of L-phenylalanine ammonia-lyase activity by L-phenylalanine showed a lag period of 1 to 1.5 h and reached a maximum around 4 to 6 h after the addition of the inducer to the medium. L-Phenylalanine, L-tyrosine, and L-tryptophan were nearly equally efficient inducers of the enzyme. D-Phenylalanine was as efficient as the L-isomer, whereas D-tyrosine was a poor inducer. Light, gibberellic acid, indole 3-acetic acid, and kinetin had no effect on the induction of L-phenylalanine ammonia-lyase activity. Cycloheximide did not inhibit the uptake of amino acids by the mycelia but completely blocked the incorporation of radioactive amino acids into soluble proteins and the development of L-phenylalanine ammonia-lyase activity. Actinomycin D inhibited both the incorporation of 32P into ribonucleic acid and the enzyme activity. Conclusive evidence for de novo synthesis of L-phenylalanine ammonia-lyase was obtained by the incorporation of radioactive amino acids into the enzyme. Electrophoretic analysis of the purified preparation showed a single protein band that coincided with radioactivity and L-phenylalanine ammonia-lyase activity. Glucose and intermediates of the tricarboxylic acid cycle, like citric acid, alpha-ketoglutaric acid, and succinic acid, and the metabolites of L-phenylalanine, like o-coumaric acid, o-hydroxyphenylacetic acid, and protocatechuic acid, significantly repressed L-phenylalanine ammonia-lyase activity. The observed repression was not relieved by cyclic adenosine 5'-triphosphate.