Tritium exchange reactions catalyzed by 2-oxo-4-hydroxyglutarate aldolase from Escherichia coli K-12.
Tritiated water and tritiated substrates have been used to study exchange reactions catalyzed by Escherichia coli 2-oxo-4-hydroxyglutarate aldolase (4-hydroxy-2-oxoglutarate glyoxylate-lyase, EC 4.1.3.16, 2-oxo-4-hydroxyglutarate in equilibrium pyruvate + glyoxylate). With pyruvate, the enzyme catalyzes a rapid first-order exchange of all three methyl hydrogens in the absence of added acceptor aldehyde (i.e. glyoxylate). This reaction is not rate limiting for aldol condensation or cleavage; quite different pH-activity profiles for the exchange reaction versus aldol cleavage and also comparative effects that pH changes have on Km and V values for the two processes favor this conclusion. The exchange reaction with 2-oxobutyrate, a substrate analog, is stereoselective; one methylene hydrogen is removed at a 6-fold faster rate than the other but eventually both are exchanged. No tritium exchange occurs with glyoxylate.[1]References
- Tritium exchange reactions catalyzed by 2-oxo-4-hydroxyglutarate aldolase from Escherichia coli K-12. Grady, S.R., Dekker, E.E. Biochim. Biophys. Acta (1979) [Pubmed]
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