EICs and mass spectra of peptide products obtained using Ma -tRNA Pyl -ACC charged with monomers 7 and 13 – 15 by Ma FRS1 ( 7 and 15 ) or Ma FRS2 ( 13 and 14 ). The insets show the mass spectra of the major ions used to generate the EIC of the translated peptide initiated with the indicated monomer. The expected (exp) and observed (obs) m / z peaks in the mass spectra are as follows: l -Phe ( 7 ) (M + 3H): exp: 420.51906, obs: 420.52249; α-SH 13 (M + 2H): exp: 638.75554, obs: 638.75614; 2-BMA ( 14 ) (M + 2H): exp: 644.76442, obs: 644.76498; N -formyl- l -Phe ( N -fPhe) 15 (M + 2H): exp: 644.27242, obs: 644.27167.
