Michael R. Thompson mthompson at
Thu Jun 10 12:22:12 EST 1999

I have used protamine sulphate to remove nucleic acids prior to isoelectric
focusing, or before purifying a recombinant enzyme. Dissolve protamine
sulphate powder in buffer and neutralize (it is quite acidic) before adding
to your protein prep. Use at a ratio (w:w) of about 1:30 of total protein.
Shake or rotate the vessel in the coldroom for about 1 hour, spin out the
precipitate afterwards. Seems to work well in both of my applications and
doesn't affect the activity of the enzyme. Protamine binds to all nucleic
acids, consequently it may also precipitate nucleic acid-binding proteins
(handy selective purification step in some applications). It may also
precipitate other proteins so you will have to check with yours.
Streptomycin precipitates ribosomes quite cleanly but doesn't remove DNA.

Silke Beismann wrote in message <375F8E6B.16B5B20D at>...
>Hi ,
>during my protein purification I have a lot of trouble to get rid of
>nucleic acids. I have to use high amounts of Benzonase, dialyse
>extensively, use several chromatography columns and so on. Now I read in
>a paper a protocoll for streptomycin sulfate precipitation of nucleic
>acids. Has anyone used this method before? Is it mild to the protein and
>efficiently in respect of the nucleic acids?
>Thanks for your answers,
>Silke Beismann

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