Rapid photodynamics of vitamin B6 coenzyme pyridoxal 5'-phosphate and its Schiff bases in solution

The Journal of Physical Chemistry. B
Melissa P HillDelmar S Larsen

Abstract

The active form of vitamin B6, pyridoxal 5'-phosphate (PLP), is an important cofactor for numerous enzymes in amine and amino acid metabolism. Presented here is the first femtosecond transient absorption study of free PLP and two Schiff bases, PLP-valine and PLP-alpha-aminoisobutyric acid (AIB), in solution. Photoexcitation of free PLP leads to efficient triplet formation with an internal conversion rate that increases with increasing pH. The measured excited-state kinetics of the PLP-valine Schiff base exhibits a dramatic deuterium dependence as a result of excited-state proton transfer (ESPT) of the Calpha hydrogen in the amino acid substrate. This is consistent with formation of the key reaction carbanionic intermediate (quinonoid), which is resonance stabilized by the electron-deficient, conjugated pi system of the Schiff base/pyridine ring. The transient absorption signals of the PLP-Schiff base with alpha-methylalanine (2-aminoisobutyric acid), which does not have a Calpha proton, lack an observable deuterium effect, verifying ESPT formation of the quinonoid intermediate. In contrast to previous studies, no dependence on the excitation wavelength of the femtosecond kinetics is observed with PLP or PLP-valine, which sugges...Continue Reading

References

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Citations

Oct 15, 2013·Archives of Biochemistry and Biophysics·Michael D Toney
Nov 10, 2010·Journal of the American Chemical Society·Melissa P HillDelmar S Larsen
May 23, 2013·The Analyst·Darshna SharmaJohn F Callan
Mar 5, 2009·The Review of Scientific Instruments·E C CarrollD S Larsen
Dec 7, 2011·Proceedings of the National Academy of Sciences of the United States of America·Giorgio GiardinaFrancesca Cutruzzolà
Nov 26, 2009·Photochemistry and Photobiology·Claudia BuenoMaría Victoria Encinas
Jan 28, 2017·Journal of the American Chemical Society·Samantha L PilicerChristian Wolf
Mar 29, 2011·The Journal of Physical Chemistry. B·Melissa P HillDelmar S Larsen
Sep 7, 2021·The Journal of Organic Chemistry·Rui-Xue JiJiang-Shan Shen

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