Fig. 2.

Characterization of RGDPEG-avidin. Panel A and B: SDS-PAGE separation followed by CBB protein staining (a) or Western blotting and anti-RGD detection (b). lane 1: MW marker, lane 2: avidin, lane 3: RGDPEG-avidin. Unmodified avidin was separated into its 15 kDa subunits, while RGDPEG-avidin was disassembled into different bands corresponding to subunits with 0, 1, 2 or 3 attached RGDPEG groups. The intrinsic heterogeneity of PEG polymers can be observed in the broadly stained band of the RGDPEG-avidin Western blot. Panel C: MALDI-TOF analysis of RGDPEG-avidin. Upper line: RGDPEG-avidin, bottom line: avidin. During ionization, the tetrameric proteins have disassembled into subunits, yielding a single peak for avidin and multiple peaks for RGDPEG-avidin corresponding to modification degree 0, 1, 2, 3, 4