title: Stereospecificity of isotopic exchange of C-α-protons of glycine catalyzed by three PLP-dependent lyases: the unusual case of tyrosine phenol-lyase.
abstract: A comparative study of the kinetics and stereospecificity of isotopic exchange of the pro-2R- and pro-2S protons of glycine in (2)H(2)O under the action of tyrosine phenol-lyase (TPL), tryptophan indole-lyase (TIL) and methionine γ-lyase (MGL) was undertaken. The kinetics of exchange was monitored using both (1)H- and (13)C-NMR. In the three compared lyases the stereospecificities of the main reactions with natural substrates dictate orthogonal orientation of the pro-2R proton of glycine with respect to the cofactor pyridoxal 5'-phosphate (PLP) plane. Consequently, according to Dunathan's postulate with all the three enzymes pro-2R proton should exchange faster than does the pro-2S one. In fact the found ratios of 2R:2S reactivities are 1:20 for TPL, 108:1 for TIL, and 1,440:1 for MGL. Thus, TPL displays an unprecedented inversion of stereospecificity. A probable mechanism of the observed phenomenon is suggested, which is based on the X-ray data for the quinonoid intermediate, formed in the reaction of TPL with L-alanine. The mechanism implies different conformational changes in the active site upon binding of glycine and alanine. These changes can lead to relative stabilization of either the neutral amino group, accepting the α-proton, or the respective ammonium group, which is formed after the proton abstraction.
authors.affiliation: Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, Russian Federation.
authors.forename: Vitalia V
authors.initials: VV
authors.lastname: Koulikova
authors.forename: Lyudmila N
authors.initials: LN
authors.lastname: Zakomirdina
authors.forename: Olga I
authors.initials: OI
authors.lastname: Gogoleva
authors.forename: Marina A
authors.initials: MA
authors.lastname: Tsvetikova
authors.forename: Elena A
authors.initials: EA
authors.lastname: Morozova
authors.forename: Vsevolod V
authors.initials: VV
authors.lastname: Komissarov
authors.forename: Yaroslav V
authors.initials: YV
authors.lastname: Tkachev
authors.forename: Vladimir P
authors.initials: VP
authors.lastname: Timofeev
authors.forename: Tatyana V
authors.initials: TV
authors.lastname: Demidkina
authors.forename: Nicolai G
authors.initials: NG
authors.lastname: Faleev
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D055162:Biocatalysis; D002247:Carbon Isotopes / Q000737:chemistry; D013437:Carbon-Sulfur Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016971:Citrobacter freundii / Q000737:chemistry / Q000201:enzymology*; D005998:Glycine / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D011514:Proteus vulgaris / Q000737:chemistry / Q000201:enzymology*; D011522:Protons; D011732:Pyridoxal Phosphate / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013237:Stereoisomerism; D014368:Tryptophanase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014447:Tyrosine Phenol-Lyase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002247:Carbon Isotopes; D011522:Protons; D011732:Pyridoxal Phosphate; D014368:Tryptophanase; D014447:Tyrosine Phenol-Lyase; D013437:Carbon-Sulfur Lyases; C021558:L-methionine gamma-lyase; D005998:Glycine