小中大
a lot of media are commercially available. 13C, 15N, 13C/15N, ( google them )
try several of these media, not all proteins are expressed efficiently in every medium so this step can be critical to optimize the level of expression.
some other information
cuturl('http://www.protein-nmr.org.uk/labelling.html')
cuturl('http://www.promega.com/pnotes/98/15963_06/15963_06.pdf')
cuturl('http://www.silantes.com/media_powder.pdf')
cuturl('http://www.sigmaaldrich.com/etc/medialib/docs/Aldrich/General_Information/1/isogro-as-media-supplement.Par.0001.File.tmp/isogro-as-media-supplement.pdf')