Buffer solutes as stabilizers of 35S-amino acids: a study of volatility, radiochemical purity and biological activity

It is well established that volatile radioactive compounds are associated with preparations of 35S-amino acids, but misconceptions still exist. The addition of stabilizers to these preparations has created a false sense of security regarding the evolution of these volatiles from cell culture medium. Experiments presented here show that the commercially used buffers L-lysine, tricine and 3,4-pyridine-dicarboxylic acid all reduced, but did not eliminate, the evolution of 35S volatiles from tissue culture medium. In each case, the rate of release was approximately 12 nCi/mCi/day (or 0.001%), compared to approximately 44 nCi/mCi/day in the buffer's absence. None of six alternative buffers tested are more effective than the commercially used buffers. We found that the release of labeled volatiles is dependent on the nature of the culture medium, but is no greater from crude 35S-amino acid preparations than from purified 35S-methionine. These commercially used buffers are also effective in maintaining radiochemical purity and are compatible with biological activity; however, because these buffers do not entirely eliminate the release of radioactivity into the gas phase, routine safe-handling procedures should be practiced when working with these products.