ESI-MS for the measurement of bovine and porcine somatotropins

Abstract

Somatotropins are proteins naturally produced by the pituitary gland in cattle. Recombinant somatotropins, which differ from their native form by several amino acids, have been synthesized in order to increase milk production in dairy cows. As their use is forbidden in Europe, control has to be performed. Until now, radioimmunoassay methods were generally used for quantification, but none is able to distinguish endogenous from recombinant somatotropins. Herein, a sensitive method based on liquid chromatography-mass spectrometry (LC-MS) and electrospray ionization (ESI) is presented in view to identify and quantify somatotropins in milk and plasma. Accuracy of the technique should allow the molecular mass differentiation between pituitary and recombinant somatotropins. The detection limit was measured at the nanogram level. As a second approach an enzymatic digestion was performed on recombinant somatotropin. A N-terminal digest proved to be specific and would allow to differentiate recombinant and endogenous proteins. Separation and detection of peptide fragments by ESI-LC-MS appear to be promising.