Stereochemical studies of the pyruvate kinase reaction with (Z)- and (E)-phosphoenol-α-ketobutyrate

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Abstract
(Z)- and (E)-phosphoenol-2-ketobutyrate were synthesized. [3-2H]-2-Ketobutyrates were formed from both isomers in the rabbit muscle pyruvate kinase reaction in 2H2O and were converted to chiral propionates. Authentic (2S)-[2-2H]propionic acid was also prepared and the optical rotatory dispersion curves of the propionates were compared. The rotation compared with standard propionate at 240 nm of sodium (2R)-[2-2H]propionate from the Z isomer was 47% (i.e., 53% was RS) and of (2S)-[2-2H]propionate from the E isomer was 29% (i.e., 71% was RS). Protonation at C-3 of the 2 si, 3 re face of the pseudosubstrates would have yielded (2R)- and (2S)-[2-2H]propionates from the Z and E analogs, respectively. An explanation offered for the nonstereoselective protonation that occurred was dissociation of the enol from the enzyme and subsequent random protonation in solution.