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. Author manuscript; available in PMC: 2017 Oct 2.
Published in final edited form as: Biochemistry. 2012 Aug 3;51(32):6342–6349. doi: 10.1021/bi3007687

Figure 1.

Figure 1

Photo-induced cross-linking of unmodified protein (PICUP). The chemistry is initiated by photolyzing Ru(II) (λmax = 452 nm) with visible light. Photolysis of this metal complex produces an excited state, which can donate an electron to persulfate, cleaving its O-O bond. The products are Ru(III), the sulfate radical, and the sulfate anion. The activated metal complex Ru(III) can abstract an electron from a nearby amino acid (Tyr, Trp, His, or Met are the most reactive). This produces a protein radical species that can then attack a wide variety of other groups on nearby proteins. This chemistry results in a covalently cross-linked protein complex without any prior modification to the protein of interest.