Synthesis ofl-Tyrosine or 3,4-Dihydroxyphenyl-l-alanine from Pyruvic Acid, Ammonia and Phenol or Pyrocatechol

Evidence for a tyrosine protonation change during the primary phototransition of bacteriorhodopsin at low temperature.

“…Our results indicate that one or more tyrosines change during the bR570 to K phototransition and suggest that a tyrosinate group in bR570 becomes protonated by K. These conclusions are strongly supported by UV difference measurements, which also suggest the possible involvement of tryptophan at this stage of the photocycle. (14) and was purified by recrystallization. All isotope substitutions were verified by NMR spectroscopy.…”

Inactivation of tyrosine phenol‐lyase by Pictet–Spengler reaction and alleviation by T15A mutation on intertwined N‐terminal arm

“…The formation of l-DOPA-PLP cyclic adducts has also been detected in the inactivation of l-DOPA decarboxylase by a substrate [10,11], eventually leading to the dissociation of the cofactor. However, despite extensive studies on TPL as a biocatalyst [2][3][4][5][6]12,13], the inhibitory effect of l-DOPA-PLP adduct formation on the enzymatic synthesis of l-DOPA has not yet been addressed.…”

“…Each subunit of C. freundii TPL is comprised of an N-terminal arm (residues [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], small domain, and PLP-binding large domain. The active site is located in a cleft surrounded by one subunit and the large domain of the adjacent subunit, constituting a catalytic dimer.…”

“…Meanwhile, at high concentrations of ammonium pyruvate, the enzyme catalyzes the synthesis of aromatic amino acids from phenolic substrates through the reverse reaction of a,b-elimination [2,3] (Scheme 1). Application of the enzyme for the synthesis of 3,4-dihydroxyphenyl-l-alanine (l-DOPA) from catechol has also attracted particular attention [4][5][6], because l-DOPA is used as a general medicine for the treatment of Parkinson's disease [7].…”

“…Meanwhile, at high concentrations of ammonium pyruvate, the enzyme catalyzes the synthesis of aromatic amino acids from phenolic substrates through the reverse reaction of a,b-elimination [2,3] (Scheme 1). Application of the enzyme for the synthesis of 3,4-dihydroxyphenyl-l-alanine (l-DOPA) from catechol has also attracted particular attention [4][5][6], because l-DOPA is used as a general medicine for the treatment of Parkinson's disease [7].Investigations on the metabolic fate of l-DOPA in biological fluids have discovered the formation of condensation adducts with endogenous aldehydes, like PLP, Citrobacter freundii l-tyrosine phenol-lyase (TPL) was inactivated by a Pictet-Spengler reaction between the cofactor and a substrate, 3,4-dihydroxyphenyl-l-alanine (l-dopa), in proportion to an increase in the reaction temperature. Random mutagenesis of the tpl gene resulted in the generation of a Thr15 to Ala mutant (T15A), which exhibited a two-fold improved activity towards l-DOPA as the substrate.…”