I'm trying to find out how to prepare Ca2+/Mg2+-free PIPES/cysteine buffer, pH 7.4, for papain digestion of murine brain. I cannot find a preparation for it online. Any suggestions?
You could add EDTA and EGTA to bind up any free Mg2+ and Ca2+ that might be present as contaminants of the water, PIPES, and cysteine. Alternatively, you could use Chelex resin to remove the metal ions.