(A) Synthesis of cross-linker 10. (B) Cross-linking Akt1 and fluorescent substrate peptide 2 with cross-linkers 1 and 10 in the presence or absence of HeLa cell lysate proteins. Akt1, fluorescent peptide 2 with or without HeLa cell lysates, were treated with either cross-linker 1 or 10 for 20 min, followed by SDS-PAGE and in gel fluorescence scanning. (C) Cross-linking of endogenous HeLa cell lysate proteins with substrate peptide 2, in the presence of cross-linker 1 or o-phthaldialdehyde. HeLa cell lysates and substrate peptide 2 were treated with cross-linker 1 or o-phthaldialdehyde for 20 min at r.t., followed by SDS-PAGE and in gel fluorescence scanning.