Fig. 2.

Raman scattering of C≡C modified substrates reports on CP chain sequestration. a Raman spectra for EcACP (blue), Act ACP (green), and Rat ACP (red), each loaded with the C₈ probe, provide information about the local environment of the C≡C probe consistent with literature precedent that a C₈ substrate chain is sequestered by EcACP, not sequestered by Rat ACP, and partially sequestered by Act ACP. b Raman spectra for C₅ (green), C₈ (blue), and C₁₃ (red) probes on EcACP show how sequestration depends on the chain length. c Spectra for C₈ probe (yellow) on Arm ACP (blue), Ben ACP (green), and WhiE ACP (red) provide chain sequestration information about previously uncharacterized ACPs. In all cases, line spectra represent data collected for probes on ACPs, and shaded bands represent data for free alkyne-labeled carboxylic acids in buffered aqueous solution. In all cases, a shift to higher frequency indicates that the alkyne probe enters a more hydrophobic environment as it becomes sequestered inside the hydrophobic pocket of an ACP. (Source data are provided as a Source Data file.)