Fig. 4. Hemosome composition as determined by high performance liquid chromatography (HPLC) and electrospray-ionisation mass spectrometry (ESI-MS). (A) Transmission electron microscopy of hemosome cores after isolation through a Percoll gradient and washing with deionised water. Scale bar, 1.0 µm. (B) Reverse-phase HPLC fractionation of the hemosome content, monitored at 220 nm. Arrow, a peak with a retention time similar to a haem standard; inset, the light absorption spectrum of the same region. (C–F) Positive-ion mode electrospray-ionisation mass spectrometry (ESI-MS) profile of the intact haem fraction (C) and tandem ESI-MS (ESI-MS/MS) spectra of its daughter ions (D–F). (G–I) ESI-MS/MS spectra of standard haem. (D,G) Daughter ions of m/z 616.4. (E,H) ESI-MS/MS spectra of the daughter ion m/z 557.4. (F,I) Tandem ESI-MS spectra of the daughter ion m/z 498.5. (J) Structure of the iron-protoporphyrin IX and the proposed assignment for its observed daughter ions.