Theoretically, citric acid can decompose into beta-ketoglutaric acid, and
the latter may decarboxylate into malonic acid...

Not sure if this happens in aqueous solutions, but if your citrate had
malonate contamination and your enzyme prefers malonate to anything else -
that's where it may have come from.

Pure speculation, of course!


> Dear all,
> i am working on a structure of M.tb, solved at 2.18 A. In my structure
> there
> is a density near to the active site and we modelled it as a malonate (C3
> O4
> H2) molecule acorrding to the density, which was not used in any of our
> buffer except we used 10 mM DTT, 1.6 M Ammonium sulphate, 100 mM citric
> acid.
> Is their any possible way to check for unknown densities or can any one
> suggest me for any possible compound which can be similar to the malonate
> or
> can be formed from above mentioned solutions (byproduct).
> Thanks
> Rajan
> --
> ************************************************
> Current Address:
> Rajan Vyas
> Research Scholar
> Deptt. of Biotechnology
> Panjab University Chandigarh, India
> 160014    Mob. +919417374197
> Fax: +91-172-2625254
> ************************************************