45. The photolysis of pyridoxal phosphate

Morrison, Alan L.; Long, Ruiling

doi:10.1039/jr9580000211

Cited by 42 publications

(47 citation statements)

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“…These results agree well with experiments in which PLP photoproducts isolated after exposure to UV light revealed that the aldehyde group first oxidizes to the acid before dimerizing (Figure 3C). 30,31…”

Section: Resultsmentioning

confidence: 99%

Light-Enhanced Catalysis by Pyridoxal Phosphate-Dependent Aspartate Aminotransferase

et al. 2010

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The mechanisms of pyridoxal 5′-phosphate (PLP) dependent enzymes require substrates to form covalent “external aldimine” intermediates, which absorb light strongly between 410 nm and 430 nm. Aspartate aminotransferase (AAT) is a prototypical PLP dependent enzyme that catalyzes the reversible interconversion of aspartate and α-ketoglutarate with oxalacetate and glutamate. From kinetic isotope effects, it is known that deprotonation of the aspartate external aldimine Cα-H bond to give a carbanionic quinonoid intermediate is partially rate limiting in the thermal AAT reaction. We show that excitation of the 430 nm external aldimine absorption band increases the steady-state catalytic activity of AAT, which is attributed to the photoenhancement of Cα-H deprotonation based on studies with Schiff bases in solution. Blue light (250 mW) illumination gives an observed 2.3-fold rate enhancement for WT AAT activity, a 530-fold enhancement for the inactive K258A mutant, and a 58,600-fold enhancement for the PLP-Asp Schiff base in water. These different levels of enhancement correlate with the intrinsic reactivities of the Cα-H bond in the different environments, with the less reactive Schiff bases exhibiting greater enhancement. Time-resolved spectroscopy, ranging from femtoseconds to minutes, was used to investigate the nature of the photoactivation of Cα-H bond cleavage in PLP-amino acid Schiff bases both in water and bound to AAT. Unlike the thermal pathway, the photoactivation pathway involves a triplet state with a Cα-H pKa that is estimated to be between 11 and 19 units lower than the ground state for the PLP-Val Schiff base in water.

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Section: Resultsmentioning

confidence: 99%

Light-Enhanced Catalysis by Pyridoxal Phosphate-Dependent Aspartate Aminotransferase

et al. 2010

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“…In aerobic conditions, the principal breakdown (oxidation) products include 4-pyridoxic acid-5 0 -phosphate and the dipyridyl a-diketone. In anaerobic conditions, the acyloin is produced (Morrison and Long 1958;Wei et al 1972;Bazhulina et al 1974).…”

Section: Discussionmentioning

confidence: 99%

Cirrhosis Associated with Pyridoxal 5′-Phosphate Treatment of Pyridoxamine 5′-Phosphate Oxidase Deficiency

et al. 2014

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We report the case of an 8-year-old boy with pyridoxamine 5 0 -phosphate oxidase (PNPO) deficiency. He developed seizures at 24 h of age that were refractory to standard anticonvulsant therapy and a trial of pyridoxine but responded to pyridoxal phosphate (PLP) at 28 days of life. Genetic testing identified compound heterozygous mutations in the PNPO gene. Management of encephalopathic episodes required escalation of PLP dose to 100 mg/kg/day by 2 years of age. Routine blood tests at this time showed significantly deranged liver function tests (LFTs). A wedge liver biopsy showed early cirrhosis with marked elevation of pyridoxal and pyridoxic acid levels in the liver sample. Despite extensive investigation, no cause other than PLP therapy could be identified for the cirrhosis. The PLP dose was weaned to 50 mg/kg/day before episodes of encephalopathy recurred. Concurrent with the reduction of his PLP dose, LFTs showed improvement. However, at 8 years of age, there is persistent evidence of hepatic fibrosis and early portal hypertension. We hypothesise that hepatic toxicity due to PLP or its degradation products is the cause of cirrhosis in this boy. Until further evidence becomes available, we would suggest that people with PNPO deficiency are treated with the minimum dose of PLP required to prevent episodes of encephalopathy.

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“…PLP was irradiated with light of wavelengths longer than 300 nm in the presence of oxygen [1]. After purification by chromatography on Dowex 1-X-8 resin, two major products were isolated: PPA and bis-PLP (Scheme I).…”

Section: Methodsmentioning

confidence: 99%

“…Bis-PNP was obtained by reduction of bis-PLP with NaBH4 [1]. To a solution of bis-PLP (pH 6), a stoichiometry concentration of NaBH4 was added and allowed to react for 1 h in an ice bath.…”

Section: Methodsmentioning

confidence: 99%

“…Irradiation of aqueous solutions of pyridoxal-5'-P (PLP) results in a decrease in the concentration of the starting compounds accompanied by the appearance of photoproducts [1,2]. Formation of the new compounds depends on the experimental conditions used in the photochemical reactions, i.e., initial concentration of PLP and the presence or absence of 02 in the reaction medium [3].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Spectroscopic properties of the photoproducts of pyridoxal-5′-P irradiation: Catalytic site recognition of ribonuclease A

Pineda

Blázquez

1994

J Fluoresc

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Photoproducts of pyridoxal-5'-P, i.e., 4-pyridoxic-5'-P and bis-pyridoxal-5'-P, have been studied by spectroscopic methods. The spectroscopic properties of bis-pyridoxal-5'-P (bis-PLP) resemble those of pyridoxal-5'-P (PLP) under similar experimental conditions. The coupling of methylen hydrogens to the phosphorus atom has been shown by NMR spectroscopy. The singlet in the(31)P-NMR spectra and the triplet in(1)H-undecoupled experiments confirm the presence of the phosphate group in the 5' position of the structure of the vitamin. The effect of pH and solvent composition on the relative distribution of species of bis-pyridoxine-5'-P (bis-PNP) has been investigated by absorption and fluorescence spectroscopy. The acid-base dissociation of the phosphate group is easily detected by emission spectroscopy. Bis-PNP and bis-PLP bind to the enzyme RNase A and they behave as competitive inhibitors with respect to the substrate cytidine-2'-3'-cyclic phosphate. The natural forms of vitamin B6, pyridoxine, and pyridoxine-5'-P have no effect on the catalytic activity of the protein. Experimental evidence derived from fluorescence and inhibition experiments is consistent with the hypothesis that bis-PNP recognizes the catalytic site of RNase A.

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45. The photolysis of pyridoxal phosphate

Cited by 42 publications

References 0 publications

Light-Enhanced Catalysis by Pyridoxal Phosphate-Dependent Aspartate Aminotransferase

Light-Enhanced Catalysis by Pyridoxal Phosphate-Dependent Aspartate Aminotransferase

Cirrhosis Associated with Pyridoxal 5′-Phosphate Treatment of Pyridoxamine 5′-Phosphate Oxidase Deficiency

Spectroscopic properties of the photoproducts of pyridoxal-5′-P irradiation: Catalytic site recognition of ribonuclease A

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