Mass spectrometry analysis of C3 structure in changing glucose. (A) A representative spectral count analysis of the biotinylation of the C3 peptide AHEAKIR containing K464. (B) Cumulative spectral counts for biotin surface modification for each of 41 lysine positions. Lysine residues that showed significant change (P < 0.05) in biotinylation correlating with changing glucose are marked with an asterisk. (C) A linear peptide map showing the domains of C3 and the relative positions of the lysines that demonstrated changing biotinylation. Lysines that showed decreased labeling as glucose increased are in italics and lysines that showed increased labeling as glucose increased are underlined. (D) Model of C3 showing the positions of lysine residues that were increasingly modified as glucose increased (green) and lysine residues that were decreasingly modified as glucose increased (blue). Other lysine residues are shown in red. 180 degree rotation of model is illustrated to show all lysines.