4-Azido-L-phenylalanine hydrochloride is an unnatural amino acid, which is used as an effective vibrational reporter of local protein environments.
In cell-free protein synthesis (CFPS) method, 0.9-1.7 mg/mL of modified soluble super-folder green fluorescent protein (sfGFP) containing either 4-Azido-L-phenylalanine or p-propargyloxy-l-phenylalanine (pPaF) accumulate in the CFPS solutions[1].
[1]. Albayrak C, et al. Cell-free co-production of an orthogonal transfer RNA activates efficient site-specific non-natural amino acid incorporation. Nucleic Acids Res. 2013 Jun;41(11):5949-63.