ESI-MS for the measurement of bovine and porcine somatotropins

Somatotropins are proteins naturally produced by the pituitary gland in cat tle. Recombinant somatotropins, which differ from their native form by seve ral amino acids, have been synthesised in order to increase milk production in dairy cows. As their use is forbidden in Europe, control has to be perf ormed. Until now, radioimmunoassay methods were generally used for quantifi cation, but none is able to distinguish endogenous from recombinant somatot ropins. Herein, a sensitive method based on liquid chromatography-mass spec trometry (LC-MS) and electrospray ionisation (ESI) is presented in view to identify and quantify somatotropins in milk and plasma. Accuracy of the tec hnique should allow the molecular mass differentiation between pituitary an d recombinant somatotropins. The detection limit was measured at the nanogr am level. As a second approach an enzymatic digestion was performed on reco mbinant somatotropin. A N-terminal digest proved to be specific and would a llow to differentiate recombinant and endogenous proteins. Separation and d etection of peptide fragments by ESI-LC-MS appear to be promising.