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Sorry for a simple and non-CCP4 question. I have determined the structures of three different mutants of a thermostable protein by X-ray crystallography method. I feel that Mg2+ has a role in protein stability. So I want to perform a thermal denaturation study by CD spectroscopy both in presence and absence of Mg2+ ion. In this regards, what should be the suitable buffer for CD studies? May I use PBS buffer ? Since phosphate sequester divalent cations like Mg2+. Is it advisable to use PBS buffer. If so, what is maximum concentration of Mg2+ ion that can be used say e.g. 5 mM? My protein was in Tris buffer and lyophilized and have theoretical pI =4.56 and maximum activity at pH 8.4. Thanking you in advances, harsh