Reversibility of the “irreversible” histidine ammonia-lyase reaction

Williams, Virginia R.; Hiroms, Janice M.

doi:10.1016/0005-2744(67)90139-8

Cited by 21 publications

(9 citation statements)

References 6 publications

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“…Unfortunately, in his experiments the concentration of NH 4 + was too low (10–60 m m ); on the basis of these and other previous experiments [56,57], he assumed that the HAL (as well as the PAL) reaction was irreversible. Later, it was shown that at higher NH 4 + concentrations (up to 6 m ) both ammonia‐lyase reactions can be completely reversed [28,58]. Nevertheless, Peterkofsky's experiments support the existence of an enzyme–NH 4 + intermediate and the idea that ammonia is released after the other product (urocanate or cinnamate).…”

Section: Resultsmentioning

confidence: 99%

An active site homology model of phenylalanine ammonia‐lyase from P. crispum

Röther

Poppe

Morlock

et al. 2002

European Journal of Biochemistry

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The plant enzyme phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) shows homology to histidine ammonia-lyase (HAL) whose structure has been solved by X-ray crystallography. Based on amino-acid sequence alignment of the two enzymes, mutagenesis was performed on amino-acid residues that were identical or similar to the active site residues in HAL to gain insight into the importance of this residues in PAL for substrate binding or catalysis. We mutated the following amino-acid residues: S203, R354, Y110, Y351, N260, Q348, F400, Q488 and L138. Determination of the kinetic constants of the overexpressed and purified enzymes revealed that mutagenesis led in each case to diminished activity. Mutants S203A, R354A and Y351F showed a decrease in k cat by factors of 435, 130 and 235, respectively. Mutants F400A, Q488A and L138H showed a 345-, 615-and 14-fold lower k cat , respectively. The greatest loss of activity occurred in the PAL mutants N260A, Q348A and Y110F, which were 2700, 2370 and 75 000 times less active than wild-type PAL. To elucidate the possible function of the mutated amino-acid residues in PAL we built a homology model of PAL based on structural data of HAL and mutagenesis experiments with PAL. The homology model of PAL showed that the active site of PAL resembles the active site of HAL. This allowed us to propose possible roles for the corresponding residues in PAL catalysis.

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Section: Resultsmentioning

confidence: 99%

An active site homology model of phenylalanine ammonia‐lyase from P. crispum

Röther

Poppe

Morlock

et al. 2002

European Journal of Biochemistry

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“…The reversibility of the HAL reaction was recognized about four decades ago 89. Under extreme reaction conditions (4 M NH 4 OH, pH 10) HAL can catalyze the reverse (amination) reaction in vitro 90.…”

Section: Use Of the Reverse Hal And Pal Reactions In Biocatalysismentioning

confidence: 99%

Friedel–Crafts‐Type Mechanism for the Enzymatic Elimination of Ammonia from Histidine and Phenylalanine

2005

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The surprisingly high catalytic activity and selectivity of enzymes stem from their ability to both accelerate the target reaction and suppress competitive reaction pathways that may even be dominant in the absence of enzymes. For example, histidine and phenylalanine ammonia-lyases (HAL and PAL) trigger the abstraction of the nonacidic beta protons of these amino acids while leaving the much more acidic ammonium hydrogen atoms untouched. Both ammonia-lyases have a catalytically important electrophilic group, which was believed to be dehydroalanine for 30 years but has now been revealed by X-ray crystallography and UV spectroscopy to be a highly electrophilic 5-methylene-3,5-dihydroimidazol-4-one (MIO) group. Experiments suggest that the reaction is initiated by the electrophilic attack of MIO on the aromatic ring of the substrate. This incomplete Friedel-Crafts-type reaction leads to the activation of a beta proton and its stereospecific abstraction, followed by the elimination of ammonia and regeneration of the MIO group. The plausibility of such a mechanism is supported by a synthetic model. The application of the PAL reaction in the biocatalytic synthesis of enantiomerically pure alpha-amino beta-aryl propionates from aryl acrylates is also discussed.

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“…[20] The reversibility of the ammonia lyase reaction that is catalysed by MIO-dependent enzymes was recognised decades ago. [21] In the presence of a high concentration of ammonia, PAL [17,22] and HAL [23] can catalyse the a-addition of ammonia to aryl acrylic acids. In contrast to the ammonia lyases, aminomutases are expected to retain the a,b-unsaturated acid in their active sites and promote the re-addition of ammonia to the bposition.…”

Section: Introductionmentioning

confidence: 99%

Enzymatic Synthesis of Enantiopure α‐ and β‐Amino Acids by Phenylalanine Aminomutase‐Catalysed Amination of Cinnamic Acid Derivatives

Szymański

Wietzes

et al. 2009

ChemBioChem

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The phenylalanine aminomutase (PAM) from Taxus chinensis catalyses the conversion of alpha-phenylalanine to beta-phenylalanine, an important step in the biosynthesis of the N-benzoyl phenylisoserinoyl side-chain of the anticancer drug taxol. Mechanistic studies on PAM have suggested that (E)-cinnamic acid is an intermediate in the mutase reaction and that it can be released from the enzyme's active site. Here we describe a novel synthetic strategy that is based on the finding that ring-substituted (E)-cinnamic acids can serve as a substrate in PAM-catalysed ammonia addition reactions for the biocatalytic production of several important beta-amino acids. The enzyme has a broad substrate range and a high enantioselectivity with cinnamic acid derivatives; this allows the synthesis of several non-natural aromatic alpha- and beta-amino acids in excellent enantiomeric excess (ee >99 %). The internal 5-methylene-3,5-dihydroimidazol-4-one (MIO) cofactor is essential for the PAM-catalysed amination reactions. The regioselectivity of amination reactions was influenced by the nature of the ring substituent.

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Reversibility of the “irreversible” histidine ammonia-lyase reaction

Cited by 21 publications

References 6 publications

An active site homology model of phenylalanine ammonia‐lyase from P. crispum

An active site homology model of phenylalanine ammonia‐lyase from P. crispum

Friedel–Crafts‐Type Mechanism for the Enzymatic Elimination of Ammonia from Histidine and Phenylalanine

Enzymatic Synthesis of Enantiopure α‐ and β‐Amino Acids by Phenylalanine Aminomutase‐Catalysed Amination of Cinnamic Acid Derivatives

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