Problems with P1 nuclease

[David Dufour Rausell]

Hello,

we are trying to synthesize NTPs marked with 13C and 15N. For this
purpose, we have grown E. coli in marked medium. After extracting the
nucleic acids with phenol, we tried to digest them with P1 nuclease
but we couldn't. We have tested the activity of the enzyme and it is
at a normal level. The buffer is ZnSO4 0.1 mM and NaAc 15 mM, so that
shouldn't be the problem.
We did an alkaline hydrolysis and there is few DNA in the sample, so
we would be very grateful for any idea that helps.

Thanks