Aconitate isomerase

The reaction catalyzed by aconitate isomerase Pseudomonas putida) in solvent involves 4% tritium transfer between the pro- S) positions of cis- and trani-aconitate 119) [Eq. (26)] ... 

A further synthesis of labeled aspartic acids 2Ia used the enzyme aconitate isomerase (EC 5.3.3.7). This enzyme interconverts cis- and frans-aconitates 238 and 239, respectively, with exchange of the 4-pro-S hydrogen. The (4S)-[4- Hi]-trans-aconitate 239, H = H, produced in H20 could be ozonized and then converted in situ with sodium periodate and glutamic oxaloacetic transaminase (EC 2.6.1.2) to (3S)-[3- H,]aspartic acid 21a, (223). This process involves (3S)-[3- Hi]oxaloacetic acid 240, Ha = H, as an intermediate. 

Enzymatic isomerization of ds-aconitate to trans-aeon itate apparently also involves proton abstraction,165 with resonance in the anion extending into the carboxylic acid group. Its mechanism may be directly related to that of the oxosteroid isomerase. However, there are other 1,3-proton shifts in which neither a carbonyl nor a carboxyl group is present in the substrate (Eqs. 13-55,13-56). 

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