Proton Transfer in methylmalonyl-CoA Epimerase From Propionibacterium Shermanii. The Reaction of (2R)-methylmalonyl-CoA in Tritiated Water

Biochem J. 1983 Sep 1;213(3):643-50. doi: 10.1042/bj2130643.


The reaction catalysed by methylmalonyl-CoA epimerase from Propionibacterium shermanii was studied in tritiated water, in the direction with (2R)-methylmalonyl-CoA as substrate, under 'irreversible' conditions. After partial reaction, even when most of the substrate had been converted into product (isolated as propionyl-CoA) essentially no solvent tritium appeared in residual (2R)-methylmalonyl-CoA. The product, however, did contain tritium, and the specific radioactivity of the (2S)-epimer was deduced to be 0.33 times that of the solvent. These results provide further support for the mechanism proposed for the epimerase-catalysed reaction in the accompanying paper [Leadlay & Fuller (1983) Biochem. J. 213, 635-642], in which two enzyme bases act respectively as proton donor and acceptor. The observed low discrimination against solvent tritium entering the product can be accounted for by a mechanism in which the release of product is slow, and the re-protonation step on the enzyme is reversible, without leading to isotopic exchange with the solvent.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acyl Coenzyme A / analogs & derivatives*
  • Acyl Coenzyme A / metabolism
  • Chemical Phenomena
  • Chemistry
  • Chromatography, DEAE-Cellulose
  • Isomerases / metabolism*
  • Malonyl Coenzyme A / analogs & derivatives*
  • Malonyl Coenzyme A / metabolism
  • Propionibacterium / metabolism*
  • Protons
  • Racemases and Epimerases / metabolism*
  • Tritium
  • Water


  • Acyl Coenzyme A
  • Protons
  • Water
  • Tritium
  • methylmalonyl-coenzyme A
  • propionyl-coenzyme A
  • Malonyl Coenzyme A
  • Isomerases
  • Racemases and Epimerases
  • methylmalonyl-coenzyme A racemase