This preprint investigates how Enterocin C, a two-peptide bacteriocin from Enterococcus faecalis, kills bacteria by targeting BacA, a membrane protein that recycles the lipid carrier undecaprenyl phosphate. Flow Induced Dispersion Analysis (FIDA), on a Fida 1 instrument, was used to measure binding of fluorescently labelled EntC1 peptide to BacA solubilised in detergent micelles, with and without the partner peptide EntC2, giving a KD of about 96 nM, and to check selectivity against related membrane phosphatases. Detergent was needed to stop the peptide sticking to the capillary, which FIDA picked up directly from the measurement. Cooperativity between the two peptides was established by isothermal titration calorimetry. It is an example of using FIDA to measure peptide binding to a membrane protein in detergent micelles, in solution.