Mechanism of the enzymic elimination of ammonia from 3-substituted aspartic acids by 3-methylaspartase
作者:Nigel P. Botting、Mahmoud Akhtar、Mark A. Cohen、David Gani
DOI:10.1039/c39870001371
日期:——
Kinetic experiments with 3-methylaspartase, using aspartic, 3-methylaspartic, and 3-ethylaspartic acid and the appropriate C-3 deuteriated isotopomers as substrates, reveal that C(3)–H bond cleavage is partially rate-limiting for 3-methylaspartic acid, much less rate-limiting for 3-ethylaspartic acid, and not rate-limiting at all for asparticacid.
The 3-methylaspartase reaction probed using 2H- and 15N-Isotope effects for three substrates: a flip from a concerted to a carbocationic amino-Enzyme elimination mechanism upon changing the C-3 stereochemistry in the substrate from R to S
作者:David Gani、Catherine H. Archer、Nigel P. Botting、John R. Pollard
DOI:10.1016/s0968-0896(99)00043-7
日期:1999.5
The mechanisms of the elimination of ammoniafrom (2S,3S)-3-methylaspartic acid, (2S)-aspartic acid and (2S,3R)-3-methylaspartic acid, catalysed by the enzyme L-threo-3-methylaspartase ammonia-lyase (EC 4.3.1.2) have been probed using 15N-isotope effects. The 15N-isotope effects for V/K for both (2S,3S)-3-methylaspartic acid and asparticacid are 1.0246 +/- 0.0013 and 1.0390 +/- 0.0031, respectively
Syntheses of (2S,3R)- and (2S,3R)[3-2h]- 3-methylaspartic acid: slow substrates for a syn-elimination reaction catalysed by methylaspartase.
作者:Catherine H. Archer、Neil R. Thomas、David Gani
DOI:10.1016/s0957-4166(00)80221-9
日期:1993.6
Mediylaspartase catalyses the slow syn-elimination of ammonia from the (2S,3R)-[L-erythro]-diastereomer of the natural substrate, (2S,3S)-3-methylaspartic acid, to give mesaconic acid. To provide material of sufficient stereochemical purity to probe the mechanism of the reaction, two synthetic routes to (2S,3R)- and (2S,3R)[3-H-2]- 3-methylaspartic acid were devised. The use of these (2S,3R)-3-methylaspartic acids revealed that the enzymic reaction does not involve C-3 epimerisation followed by normal anti-elimination, ruling-out the possibility of a carbanion intermediate. Conversely, the substrate displayed very large primary deuterium isotope effects indicating rate-limiting C-H bond cleavage.
AKHTAR, MAHMOUD;BOTTING, NIGEL P.;COHEN, MARK A.;GANI, DAVID, TETRAHEDRON, 43,(1987) N 24, 5899-5908
作者:AKHTAR, MAHMOUD、BOTTING, NIGEL P.、COHEN, MARK A.、GANI, DAVID
DOI:——
日期:——
BOTTING, NIGEL P.;AKHTAR, MAHMOUD;COHEN, MARK A.;GANI, DAVID, J. CHEM. SOC. CHEM. COMMUN.,(1987) N 18, 1371-1373
作者:BOTTING, NIGEL P.、AKHTAR, MAHMOUD、COHEN, MARK A.、GANI, DAVID