Mechanism and stereochemistry of a,b-elimination of L-tyrosine catalysed by tyrosine phenol-lyase
Faleev N.G., Lyubarev A.E., Martinkova N.S., Belikov V.M.
Enzyme Microb. Technol., 1983, v. 5, p. 219-224
The decomposition of L-tyrosine and its a-deuterated analogue under the action of extracts from Escherichia intermedia A-21 with high tyrosine phenol-lyase [L-tyrosine phenol-lyase (deaminating), EC 188.8.131.52] activity has been studied. The mass spectrometric data for samples of phenol produced by decomposition of deutero-L-tyrosine in water and D2O-water (10:1) mixture, and by decomposition of normal L-tyrosine in D2O-water (10:1), show that the process is accompanied by the intramolecular transfer of D or H to the leaving phenol group. The degree of transfer is 7-10%. Thus, the abstraction of a-proton and the subsequent protonation of the aromatic ring are accomplished by the same functional group of the enzyme. This is indicative of the cis-orientation of a-proton and the phenol fragment in relation to the plane of Schiff's base of a-aminoacrylate with pyridoxal phosphate during a,b-elimination. The isotope effect of the studied enzyme reaction is ~3, which allows us to consider the a-proton abstraction as the limiting stage of the process.
Титульный лист | Физико-химическая биология