Figure 4

Mass spectrometric proof of the conjugation of PM20 to Cys286 in agAP-AChE.
Upper panel: high-resolution Fourier transform mass spectrometry survey scan of the [M+H]+2 ion (m/z of 1082.6122) corresponding to the PM20-labeled fragment of agAP-AChE with calculated (cal.) m/z of 1082.6120. Middle panel: supporting tandem mass spectrum showing the observed b- and y-type ions resulting from fragmentations of the [M+H]2+ ion. Lower panel: mechanisms for the oxazolone formation and b-ion cyclization.