Figure 2.

Mass spectrometry of insulin variants. a-d. Characterization of proline analog incorporation. The solubilized inclusion body (containing proinsulin) after expression in medium supplemented with proline (a), 4R-Me (b), 4S-Me (c), or 4ene (d) was digested with Glu-C and analyzed by MALDI-TOF MS. The peptide that contains position B28 of mature insulin is ⁵⁰RGFFYTPKTRRE (expected m/z = 1557.8). e-h. MALDI-TOF characterization of mature and purified insulin variants: human insulin (e), ins-4R-Me (f), ins-4S-Me (g), and Ins-4ene (h). The peaks at m/z ∼6050 correspond to adducts of the sinapic acid matrix.