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I would check CMP Kinase - does it have similar selectivity? Differences between C and U (especially with respect to hydrogen bonding of the base) are not necessarily all that minimal - most likely the enzyme employs a few strategically positioned residues to create hydrogen bonding networks that favor U over C. Which also means that the phosphate-cleaving residues have to swing into action when the correct base is recognized, meaning that I wouldn't be surprised at all if at least one of the catalytic residues is also shared with the substrate-specificity residue set. Just a guess, of course. Too busy to look it up :) Artem www.harkerbio.com - Cosmic Cats approve of this message On Fri, Aug 14, 2015 at 5:44 PM, Faisal Tarique <[log in to unmask]> wrote: > Hi everyone > > I am working on a nucleoside phosphatase which shows different substrate > specificity for uridine monophosphate (UMP) and cytidine monophosphate > (CMP). Although the difference between the two bases are minimal, but the > enzyme has higher preferential for UMP than CMP. Can anybody suggest me a > reason for this difference, or an example where similar pattern was > observed for any other enzyme. What could be the satisfying explanation and > speculation for this difference. > > -- > Regards > > Faisal > School of Life Sciences > JNU > >