I would say it really depends on what you are aiming at when making the lysate. In general 300 mM is about double ionic strength and osmolarity that nature provides the cells with (which is 140 mM), keeping in mind that inside cells there is actually KCl. So higher osmolarity will help lysing cells (by implosion), higher ionic strength as already stated will help breaking down protein complexes and interactions and solubilizing proteins. In these conditions pull-downs and IPs are quite stringent, so weaker interactions will be lost and only tight ones will be detected. Might be good for studying certain sticky proteins.
As viviana stated thats true..NaCl helps to mimic the physiological condition..it also gives ionic strength during the purification with IMAC (NI-NTA) matrix and sometimes helps in binding with the NI-NTA..if your protein does not binding or less binding with the matrix, we prefer high concentration of NaCl as well...after purify the protein its better to dialysis the protein with lower concentration of NaCl such as 150mM...
Despite mimicking the physiological condition, NaCl can basically help to increase the ionic strength of the native or denaturing purification buffers. It helps to remove the contaminants from the Ni-NTA resin by reducing the non-specific hydrophobic and ionic interaction binding between the protein. Usually up to 2M NaCl can be used in the buffers. In my experience, it provides better washing and elution of the his-tagged protein with higher purity.
You will have more proteins in the solution by using a high NaCl concernation buffer after a spin.
I would say it really depends on what you are aiming at when making the lysate. In general 300 mM is about double ionic strength and osmolarity that nature provides the cells with (which is 140 mM), keeping in mind that inside cells there is actually KCl. So higher osmolarity will help lysing cells (by implosion), higher ionic strength as already stated will help breaking down protein complexes and interactions and solubilizing proteins. In these conditions pull-downs and IPs are quite stringent, so weaker interactions will be lost and only tight ones will be detected. Might be good for studying certain sticky proteins.
Many buffers contain NaCl to help keep proteins soluble and to mimic physiological conditions. In chromatographic separations, like gel filtration and Ni2+ affinity columns, you may want to increase the salt concentration even more. I’ve gone up to 500 mM NaCl to give ionic strength which helps prevent nonspecific interactions between proteins and the column
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