Pressure and Temperature Effects on the Formation of Aminoacrylate Intermediates of Tyrosine Phenol-lyase Demonstrate Reaction Dynamics
- Univ. of Georgia, Athens, GA (United States)
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Tennessee Wesleyan Univ., Athens, TN (United States)
- Univ. of Manchester (United Kingdom)
The structures of aminoacrylate intermediates of wild-type, F448A mutant, and perdeuterated tyrosine phenol-lyase (TPL) formed from l-tyrosine, 3-F-l-tyrosine, S-ethyl-l-cysteine, and l-serine, with bound 4-hydroxypyridine, were determined by X-ray crystallography. All the aminoacrylate Schiff’s base structures in chain A are identical regardless of the substrate used to form them. 4-Hydroxypyridine is also in an identical location, except for F448A TPL, where it is displaced about 1 Å due to the increased size of the active site. In chain B, we have found different complexes depending on the substrate. With wild-type TPL, l-tyrosine gave no density, 3-F-l-tyrosine gave a gem-diamine, and l-serine gave a gem-diamine in chain B. S-Ethyl-l-cysteine formed an aminoacrylate in chain B with both wild-type and F448A TPL, but perdeuterated TPL with S-ethyl-l-cysteine formed a gem-diamine of aminoacrylate. The kinetics of aminoacrylate intermediate formation from l-tyrosine and S-ethyl-l-cysteine were followed by stopped-flow spectrophotometry at temperatures from 281 to 320 K and hydrostatic pressures ranging from 1 bar to 1.5 kbar at 293 K. There are large negative values of ΔS‡, ΔCp‡, ΔV‡, and Δβ‡ for aminoacrylate intermediate formation for l-tyrosine but not for S-ethyl-l-cysteine. Formation of the aminoacrylate intermediates from l-tyrosine and S-ethyl-l-cysteine shows heavy enzyme deuterium kinetic isotope effects with perdeuterated TPL that are strongly temperature- and pressure-dependent and may be normal or inverse depending on conditions. Overall, these results suggest that conformational dynamics as well as vibrational coupling play a key role in the mechanism of the elimination reaction of l-tyrosine catalyzed by TPL.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- National Institutes of Health (NIH); USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- AC05-00OR22725; W-31-109-ENG-3
- OSTI ID:
- 1761712
- Alternate ID(s):
- OSTI ID: 1598026
- Journal Information:
- ACS Catalysis, Journal Name: ACS Catalysis Journal Issue: 3 Vol. 10; ISSN 2155-5435
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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