1979
DOI: 10.1002/9780470122952.ch1
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Tautomerism in Pyridoxal Phosphate and in Enzymatic Catalysis

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Cited by 19 publications
(4 citation statements)
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“…In the absence of substrate molecules, all PLP-dependent enzymes covalently bind PLP in the active site as an “internal” Schiff base with a conserved lysine residue . The binding of an amine-containing substrate molecule to the enzyme results in the formation of an “external” Schiff base that, in the course of catalysis, loses an electrophile (e.g., H + or CO 2 ) to form a high-energy carbanion intermediate, termed the “quinonoid”, central to all PLP-catalyzed mechanisms. , Each tautomer and intermediate of a PLP-Schiff base has a distinct spectroscopic signature enabling isolated PLP and PLP-Schiff bases to be used as model compounds in numerous chemical and spectroscopic studies to gain insight into the mechanisms involved in PLP enzymatic catalysis. ,,,− Here, we present the first femtosecond investigation of the photodynamics for free PLP and its Schiff base with valine and α-aminoisobutyric acid (AIB) in aqueous solution (Figure ). The signals measured for the PLP Schiff base with α-methylated amino acid, AIB, are compared to those for the PLP-valine Schiff base since AIB lacks an α-proton whose cleavage is necessary for the excited-state proton transfer (ESPT) formation of the quinonoid intermediate in the transamination (Figure ).…”
Section: Introductionmentioning
confidence: 99%
“…In the absence of substrate molecules, all PLP-dependent enzymes covalently bind PLP in the active site as an “internal” Schiff base with a conserved lysine residue . The binding of an amine-containing substrate molecule to the enzyme results in the formation of an “external” Schiff base that, in the course of catalysis, loses an electrophile (e.g., H + or CO 2 ) to form a high-energy carbanion intermediate, termed the “quinonoid”, central to all PLP-catalyzed mechanisms. , Each tautomer and intermediate of a PLP-Schiff base has a distinct spectroscopic signature enabling isolated PLP and PLP-Schiff bases to be used as model compounds in numerous chemical and spectroscopic studies to gain insight into the mechanisms involved in PLP enzymatic catalysis. ,,,− Here, we present the first femtosecond investigation of the photodynamics for free PLP and its Schiff base with valine and α-aminoisobutyric acid (AIB) in aqueous solution (Figure ). The signals measured for the PLP Schiff base with α-methylated amino acid, AIB, are compared to those for the PLP-valine Schiff base since AIB lacks an α-proton whose cleavage is necessary for the excited-state proton transfer (ESPT) formation of the quinonoid intermediate in the transamination (Figure ).…”
Section: Introductionmentioning
confidence: 99%
“…In the absence of enzyme, the resulting Schiff base is stabilized through binding and coordination of metal ion by the hydroxyl group 7. In enzymatic catalysis, the metal ion is not required because of stabilization by the amino acid side chains of the enzyme 8. The binding of metal by PM at physiological pH is possible because of the unusually acidic ionization constant of the phenolic hydroxyl, pK ∼3.4 9,10.…”
Section: Introductionmentioning
confidence: 99%
“…7 In enzymatic catalysis, the metal ion is not required because of stabilization by the amino acid side chains of the enzyme. 8 The binding of metal by PM at physiological pH is possible because of the unusually acidic ionization constant of the phenolic hydroxyl, pK ∼3.4. 9,10 PM can form complexes with a number of transition metal ions but has a preference for Cu 2+ and Fe 3+ .…”
Section: Introductionmentioning
confidence: 99%
“…This tautomer has been observed in model systems in solution and is favored in hydrophobic environments. Metzler (1979) suggested that AATase uses specific hydrogen‐bonding interactions to stabilize the 430‐nm absorbing ketoenamine (I) over the enolimine tautomer(II). It is probable that the hydrogen bond from tyrosine 225 to the 3′ oxygen of PLP contributes importantly to this stabilization.…”
Section: Discussionmentioning
confidence: 99%